RESERVOIR ECOLOGY AND FISHERY MANAGEMENT A LITERATURE REVIEW AND APPLICATION TO UBOLRATANA RESERVOIR THAILAND Dissertation fix the Degree of Ph. D. MICHIGAN STATE UNIVERSITY THIRAPHAN BHUKASWAN 1973 I—I_-—I_-—-_-_-—l_-_-_-—l This is'to certify that the thesis entitled Reservoir Ecology and Fishery Management A Literature Review and Application to Ubolratana Reservoir Thailand presented by Thiraphan Bhuka swan has been accepted towards fulfillment of the requirements for Ph .D, degree in Fisheries 5: Wildlife Major professor Date November 9, 1973 0-7639 ‘1. ‘- " *nnrflsn’fir 'L‘ BOOK BIND?“ INC. 1.” LIBRAHI amoens I IPRIIEPM" u uuuuuuu . f;;..,.,-. “MW “Db ’ A 135" x4 ' ‘ .y'w—"I «i .. A l I 3"" 'AFA” - as. New ccndit atadstics cf t Light Penet ratic T ABSTRACT RESERVOIR ECOLOGY AND FISHERY MANAGEMENT A LITERATURE REVIEW AND APPLICATION TO UBOLRATANA RESERVOIR THAILAND By Thiraphan Bhukaswan The construction of dams either Single or multi-purpose, for irrigation, hydro—electric generation, flood control, and water—supply has many effects on water quality. Investigations show that after a dam is closed the properties of water changed both physically and chemiCally. Changes affect biological activities, especially the fisheries, either in the reservoir itself or in the river below the dam. New conditions of impounded water are usually affected by char- acteristics of the dam site, inundated areas, the soils, the morpho- metric characteristics of a reservoir, and fluctuation of climatic conditions. In general, the physico—chemical conditions developed following the closure of the dam are favorable to the uses of water and the development of biological activities in the impoundment. A reservoir usually acts as a settling basin and reduces the turbidity of water. Light penetration is deeper than in river conditions. Temperature is increased because of longer time exposure to the sun. However, thermal stratification always develops in deep reservoirs either in the summer or the winter. The concentration of dissolved oxygen slightly decreases Era—3““. V ' ‘ -Ar\‘t"" . asp-o‘- " ‘- I qv 'v" 5 -t"vvo"' » J.“L‘ 4., MB '- n ‘ ‘~ -'~ .GLC. a- gid‘ p. .46 e ma. ever, r C 8 uhl t O t 9'.- .l. u! a» “ lldble- V\ I‘ a Thiraphan Bhukaswan from river conditions. Carbon dioxide usually increases in deep water particularly in the hypolimnion. Biogenic salts accumulate in large quantities in the first few years of impoundment. These conditions encourage the blooms of phytoplankton and algae, then followed by increased zooplankton and numbers and total biomass of fish. The production of fish in reservoirs usually reaches its peak within the first few years after the impoundment. Then it declines rapidly in the years after to a much lower level which may maintain or gradually rise to somewhere near half the magnitude of the initial high productivity. Therefore, it is desirable to adjust the yield and smooth its fluctuating fish production at a high level near the optimum pro- ductivity of a reservoir. For this purpose, several management techniques have been practiced and their successes reported. The promising activi- ties fall into 3 categories: (1) the manipulation of the habitats; (2) the management of fish populations and their food supply based on the biology of individual species; and (3) the regulations of the fisheries. It is evident that most reservoirs have greatly increased fish production over river conditions in many countries all over the world, However, the production usually fluctuates from year to year after the initial high production period. The degree of fluctuations is correlated to the changes in environmental conditions, length of the food chain, and the success of management activities. The literature survey in reservoir ecology and the fishery manage- ment is for the purpose of applying possible management techniques to improve fish production of reservoirs in Thailand. The Ubolratana Reservoir is chosen for this purpose because more basic data are available. However, studies indicate that there is still inadequate data on the physico~chemical conditions and other biological developments .- a: ’3" .. «‘m-V I. ‘M" 'O‘x ’74. Thiraphan Bhukaswan in hand. It was difficult to propose any speCific management programs for the fishery development of this reservoir. Therefore, recommendaticns are discussed broadly on general problems that are usually encountered in reservoirs in all parts of the world with emphasis on reservoirs in the tropics. VIA. .\ RESERVOIR ECOLOGY AND FISHERY MANAGEMENT A LITERATURE REVIEW AND APPLICATION TO UBOLRATANA RESERVOIR THAILAND By Thiraphan Bhukaswan A DISSERTATION Submitted to Michigan State University in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY Department of Fisheries and Wildlife 1973 c " fln—.. SLEAtw-J‘ '\ [A ‘0 ad "‘I Q? \ 1 s ACKNOWLEDGEMENTS I wish to express my sincere appreciation to Dr. Peter I. Tack, Chairman of my doctoral committee, for his invaluable assistance, guidance, and encouragement of this study, and also to the members, Dr. Howard E. Johnson, Dr. Eugene w. Roelofs, and Dr. Milton H. Steinmuller. I am grateful to Mr. Chirdchai Amathyakul, Director of Inland Fisheries Division, and to Mr. Vanich Varikul, Senior Fishery Biologist, Department of Fisheries, Bangkok, Thailand, who supplied valuable data for this study. I appreciate the financial support of this study provided by the Royal Thai Government. ii TABLE OF CONTENTS ACKNOWLEDGEMENTS . . . . . . . . . . . . . . LIST OF TABLES . . . . . . . . . . LIST OF FIGURES. . . . . . . . . . . . . . INTRODUCTION . . . . . . . . . . . . . . . . RESERVOIR ECOLOGY. . . . . . . . . . . . . . Morphological Characteristics . . . . Type of Reservoirs . . . . . Location Characteristics . Climatic Conditions. . . . Morphometric Factors . . . . . Physical Characteristics. . . . . . . Light Penetration. . . . . . . Temperature. . . . . . . . . . Thermal Stratification . . . . Artificial Destratification. . Evaporation. . . . . . . . . . Turbidity. . . . . . . . . . . Sedimentation. . . . . . Water—Level Fluctuations Chemical Characteristics. . . . Oxygen . . . . . . . . . . . . Carbon Dioxide . . . . . . . . Acidity and Alkalinity . . . . Hydrogen-Ion Concentration . . Nitrogen . . . . , . . . . Phosphorus . . . . . . . . . . Sulfur . . . . . . . . . . . . Iron . . . . . . . . . . . . . Manganese. . . . . . . . . . Nutrient Removal . . . . . . . Aquatic Productivity. . . . . . . . . Phytoplankton. . . . . . . . . Aquatic Macrophytes. . ZOOpIankton. . . . . . . . Benthos. . . . . . . . . . . . Ichthyofauna . . . . . . . . . iii Page ii vii 9“ v- I I i I I I w t I E 1‘ s“ ! I $155 a; ’ I I g E .-..ii ”'"V R~.'. (I H U1 (1 F' at (i 5." ' D J. ) Lfln'uflm'C'U () I ..... x . . I‘D-n! ‘ . _ “R h “an". 1" I" _—___ m FISHERY EIANAGEI‘ENT O O O O 0 O C O O O O 0 Management of Habitats. . . . . . . . Timber Clearing and Brush Shelters . . . Fish Passage . . . . . . . . . Artificial Spawning Ground . . Control of Aquatic Vegetation. Fish P0pulation Studies . . . . . . . Species Composition of Fish. . Population Distribution. . . . Estimate of Fish Population. Age Composition. . . . . . . . Growth Study . . . . . . . . . Management of Fish POpulation . Selective Killing of Undesirable StOCking O O O O O O O O O O 0 Increasing of Food Supply to Fish. Regulation of Water-Level. . . Management of Tail-Waters. . . Species Elimination of Fish Parasites and Diseases Fishing Regulations and Controls. . . FISH PRODUCTION O O O O O O O O O O O O O O 0 THE STUDY OF UBOLRATANA RESERVOIR, NORTHEAST Pre—Impoundment Study . . . . . . . . Post-Impoundment Study. . . . . . . . Standing Crops. . . . . . . . . . Commercial Catches. . . . . . . . . . Fish Transplantations . . . . . . . Conclusions and Recommendations . . . Discussion. . . . . . . . . . . . . . SWRY O O O O O I O O O O O O I O O O O O 9 LITERATURE CITED 0 C O O O O O I O O O O O 0 iv Page 89 92 92 94 97 99 117 117 119 122 133 136 145 145 151 155 158 161 166 175 179 194 194 195 200 201 205 208 215 217 226 0 I LA) O) fl) 1 I“ f. II I (I) f.) m ’4 (‘1 at r. C (M I. f1 I U: 31' 00 w- (I) Table 10 11 12 LIST OF TABLES Quantitative indices from summer 200plankton in the major zones of a reservoir and upper river in the SOViet Union. I O O O O O O O O O O O O O O O I O O O O 0 Some herbicides and their effectiveness in controlling algae O O O O O 0 I O O O O C O O O O O O O O O O O O O 0 Some herbicides and dosages recommended to control floating and emergent aquatic plants. . . . . . . . . . . Some herbicides and dosages recommended to control submerged aquatic plants. . . . . . . . . . . . . . . . . Aquatic plants eaten by the grass carp, Ctenopharyn- godbn idéZZus Val., in approximate order of preference. . Estimates of total populations of threadfin (T) and gizzard (G) shad in Bull Shoals Reservoir and Beaver Reservoir in the summer 1966. . . . . . . . . . . . . . . The relationship between single environmental factors and standing crOp and harvest in 127 U. S. reservoirs . . Logarithmic partial correlation of environmental variables with total fish standing crop of 140 reser- voirs (44 hydropower mainstream, 37 hydropower storage, and 59 non-hydropower reservoirs). . . . . . . . Estimated weight of sport harvest in pounds per acre of surface water from Rough River before and after impomdmnt 0 O O O O O O I O O O O O O C I I O O O O O 0 Commercial fish catch from Missouri River mainstem reservoirs in 1963. . . . . . . . . . . . . . . . . . . . Commercial harvest in Lake Francis Case, 1959 to 1968 . . Multiple regression equations relating clupeid standing crOp, sport and commercial harvest to various combina- tions of physico-chemical factors which were selected by a step-down procedure as being most highly significant and with a relatively high R2 value . . . . . . . . . . . Page 74 106 107 109 115 133 180 182 185 186 188 191 J.» r. G a. .9 ._ .L .h a . a an,“ «.1 .Aw I\ .b n.» e k _. . ”I“ .‘J .R.. .1. nlv c L 1 0 al 9 A I I I I I I I I I I I I I II III III III I Ill: III -.I .I I. 1.. fifiilshb, rlv u". Table 13 14 15 16 17 18 Page Percentage by weight of major groups of fish found in Ubolratana Reservoir during pre- and post-impoundment periOdS O O O O O O O O O O O O O O O O O O O O O O O C O O 195 Pre- and post-impoundment fish Species found in Ubolratana Reservoir, Khon Kaen, Thailand . . . . . . . . . 197 Total yield of dominant species taken from Ubolratana Reservoir by the rotenone method. . . . . . . . . . . . . . 200 Relationship between standing cr0p (rotenone sampling) and commercial catch in Ubolratana Reservoir, Khon Kaen, Thailand, during 1965-1971. . . . . . . . . . . . . . 202 Comparison of standing crOp (rotenone sampling) and commercial catch (annual catch statistics) of four economic groups of fish from Ubolratana Reservoir, Khon Kaen, Thailand, during 1969-1971 . . . . . . . . . . . 203 Total commercial catch from Ubolratana Reservoir, Khon Kaen, Thailand, during 1966-1971 . . . . . . . . . . . 204 Figure 10 11 12 13 14 LIST OF FIGURES Summer stratification in mainstream reservoir . . . . . . Current tilted thermocline in mainstream reservoir. . . . Summer stratification in storage reservoir. . . . . . . . Winter stratification in storage reservoir. . . . . . . . Diagrammatic representation of the surface of the sedi- ment that would be accumulated in Lake Mead when the lake is filled to permanent spillway level. . . . . . . . Solubility of oxygen in distilled water saturated with air at 760 mm Hg. 0 O O I l O O O O O O O D O O O O O O 0 Dependence of the Specific rate of photosynthesis on temperature and phytoplankton concentration . . . . . . . Formation of the ichthyofauna in the Goczalkowicz ReserVOir, Poland 0 O O O O O O O O O O O O O O O O O O 0 History of a hypothetical reservoir fisheries . . . . . . Selective withdrawal from reservoir through several penstock intakes at various levels in dam . . . . . . . . Annual catches of plankton feeding, benthos feeding, and predatory fishes in Tsimlinsk Reservoir, USSR . . . . Relative annual catch of spawning char in weight during the periOd 1937—1950 C O O O O O O O C O O O O O 0 Monthly commercial catch from Ubolratana Reservoir, Khon Kaen, Thailand, during July 1966 to December 1971. . The relationship between annual water-level fluctuations and commercial catch in Ubolratana Reservoir, Khon Kaen, Thailand, during October 1970 to September 1971 . . vii Page 16 16 18 19 35 41 43 84 91 163 183 184 206 207 INTRODUCTION The construction of reservoirs is increasing rapidly in all parts of the world either on rivers, natural lakes, or valleys where the water level can be raised by dams for multi-purpose uses. Such purposes include irrigation, hydroelectric generation, flood control, public water supply, recreation, navigation, and the fisheries. In the United States, exclusive of Alaska and the Great Lakes, reservoirs have pro- duced more water acreage than there are of natural lakes (Lagler, 1971). Compilation records of the U. S. reservoirs (over 500 acres) up to January 1970, showed 1,350 reservoirs totalling 9,142,000 acres at mean annual pool levels (Jenkins, 1970c). In the Soviet Union, records in 1961 indicated a total area of reservoirs about 9,700,000 acres with an additional 37,000,000 acres in various stages of construction or planning (Frey, 1967). In Africa, reports on man-made lakes just completed and those under construction total 5,000,000 acres (Worthington, 1966). A lot more were constructed in Europe, North and South America, Australia, and Asia; unfortunately, they are not reported by numbers and acreage. Estimation based on data from a report of the U. S. President's Science Advisory Committee in 1967 on "The World Food Problem" indicated that reservoirs of the world total 66,000,000 acres in surface areas. This figure is expected to double by the year 2000. Scientists began to study the possible use of reservoirs for fishery purposes in the early 19205. Some viewed reservoirs as "bio- logical deserts" because of low fish productivity after the first few 1 2 years of high production. Intensive forms of management were applied in hope of solving the problems. Studies have been carried out in various countries throughout the world particularly in the United States, and the Soviet Union, and large numbers of publications have been contributed. With new ideas and techniques in reservoir management, it makes believable that unproductive conditions following the initial phase of high production can be solved. Evidences for this have been found in reservoirs of many countries such as in the United States, Soviet Union, Sweden, Poland, Rhodesia, Zambia, and India. These man-made lakes are becoming increasingly important to inland fisheries in many parts of the world. In the United States alone, excluding Alaska and the Great Lakes, reservoirs now comprise about 40 percent of all inland public fishery resources (Jenkins, 1970c). The objectives of this study are: 1. To present general information on the physical, chemical and biological characteristics of the reservoirs for management purposes. 2. To provide a concise summary of current information on investi- gations, applications, and evaluations of reservoir fisheries as a tool of management programs. 3. To apply promising management techniques to certain reservoir conditions to increase fishery yields. Literature on reservoir ecology and management is voluminous. Each year more studies on these problems are published in many languages. This investigation has limited its bibliography to the end of 1972 and only certain papers appearing in the first half of 1973 are included. The literature survey is based mainly on papers from the studies on reservoirs of the United States, the Soviet Union, others include 3 Canada, Poland, Germany, Sweden, Norway, Czechoslovakia, Austria, Great Britain, Israel, Ghana, Rhodesia, Zambia, and India. Data on the Ubolratana Reservoir in this study are used by courtesy of the Inland Fisheries Division, Royal Thai Fisheries Department, Bangkok, Thailand. RESERVOIR ECOLOGY The effect of reservoirs on the aquatic ecosystem has been under investigation for years. Newly created impoundments cause changes in several conditions of former water bodies neither inherent in, nor the result of operation of the dam. The physical and chemical changes that occur after the completion of reservoir exert a significant influence on the development of phytoplankton, zooplankton, and bottom fauna of the impoundment, as well as on the feeding and the growth of fish. Therefore, a study of these conditions and their processes of develop- ment in a reservoir is necessary to the management program and estimation of fishery potential of the impoundment. MORPHOLOGICAL CHARACTERISTICS The process of biological production in reservoirs is determined by morphology and the purposes of dam construction, plus its back-water characteristics. These factors have been widely recognized as the majsr determinants of trophic condition in artificial water bodies. Types of Reservoirs A reservoir is a body of water formed by the accumulation of waters as a result of the construction of the dam. In the United States, it refers to an artificial water body with the surface area not less than 500 acres. In general, reservoirs are classified into several types depending mainly on objectives of their constructions. 5 Ellis (1937) classified reservoirs on the basis of water supply namely the pond-type, lake—type, and river—type. He described a pond- type as a small artificial water body which is intermitten and often with a water supply inadequate to replace the water lost by evaporation. This type of impounded water may have concentration of electrolytes, inroads of aquatic vegetation, and depletion of oxygen. The lake-type is a larger impoundment in which the water intake is sufficient to overbalance the loss by evaporation and the inflow of the impounded stream is not a major factor in the hydrodynamics. This type of impound- ment approaches natural lake conditions except as this impounded water is disturbed by draw-down. The river—type is a long narrow impoundment as a result of dam construction across a river to slow down the flow. The slowing down of current usually causes heavy sedimentation several miles above the dam. This characteristic causes a destructive change to the bottom fauna. Zhadin and Gerd (1961) divided reservoirs according to the site of dam construction (river, running-lakes, valley of river flowing from a lake or in a waterless valley) as river-type, lake-type, and waterless- valley type. Furthermore, they are also classified depending upon type of impoundments. In case a reservoir has remained more or less confined to a narrow river valley and has flooded only a small fraction of the river's catchment areas, it is a channel type. A reservoir that has spread over a large area, flooding lands or forests many times greater in area than the water body previously existing on its site, it is known as the lobed type. Wiebe (1960) used certain morphometric, physical, and biological characteristics of the impoundments to divide reservoirs into storage type and mainstream type. The differences of these two types are given 6 in detail. The storage type is much deeper and has steeper shoreline than the mainstream reservoir; thermal stratification developed; and frequently during the summer exhibit the phenomenon of density currents that may cause an atypical distribution of dissolved oxygen with respect to the depth. Another difference is the greater transparence of the water in the storage lakes; therefore it is better suited for game fish, such as black bass and walleye, than the mainstream lakes. 0n the other hand, the water in mainstream reservoirs is more fertile, mainly because of the discharge of municipal sewage and more fertile watershed. This type of reservoir is shallow, and absent of thermal stratification. This permits the development of benthos (insects, worms, and clams) to provide a larger volume of food than that present in deep storage reservoirs. However, investigators now usually classify reservoirs basically on the initial purposes of the dam constructions. Thus, they are divided into flood control reservoir; storage reservoir; hydro-electric reser- voir; and multi-purpose reservoir (Ellis, 1941; Martin and Hanson, 1948; Parsons, 1958; Jackson, 1966; Bennett, 1970; and Jenkins, 1970). 1. Flood Control Reservoir: The conStruction of flood control reservoirs has contributed materially to the protection of downstream urban, municipal, and industrial developments by retention of flood- flows. All of this type of reservoir are located on relatively small streams. Water levels are highest during months of heavy rain. Water is discharged through conduits near the bottom of the reservoir; rarely does water pour over the spillway. It may be turbid during the rainy season, but is usually clear. 7 2. Storage Reservoirs: The storage reservoirs are needed to hold water runoff for irrigation, navigation, industrial or domestic uses. This type of reservoir is frequently created by damming permanent streams or small rivers. Water levels are high in the rainy season and low during the dry period. 3. Hydro-electric Reservoirs: The hydro-electric reservoirs are mainly located on tributary streams or rivers for the primary purpose of producing electricity. The water levels are usually highest in rainy season and spring. Water is drawn through turbines at the base of the dam, while surplus water frequently passes over spillway. Storage water is usually clear except after heavy rains. 4. Multifipurpose Reservoirs: The multi-purpose reservoirs are built for a combination of the previously listed purposes. This type of reservoir is located on large rivers. Water levels remain relatively stable, except during the periods of flood or extreme draught. The water is drawn through turbines at the base of the dam, or through locks for navigation. Impounded water may be relatively turbid for several months. Location Characteristics Conditions that will develop in the reservoirs can be predicted with considerable accuracy before the dam is built, if the composition of the water tributary to the impoundment area and type of dam are known. In some situations, it does appear that characteristics of watershed and type of soils at the dam sites play an important role on quality of impounded water. Attention has been devoted to soils with high organic contents which are responsible for undesirable effects. These may 8 include an increase in water color, decrease in dissolved oxygen, release of nutrients causing algae growth, decrease in hydrogen-ion concentration and alkalinity, and increase in dissolved solid materials (Sylvester and Seabloom, 1965). These factors will continually change with reservoir aging as a result of soils being leached and biological degradation, and by being covered with settleable solids brought in by supply streams, water runoff, and sedimented algal cells or other forms of aquatic organisms. As the newly sedimented materials degrade rapidly from biologic actions, they may have a very serious effect on the overyling water quality. Climatic Conditions The nature of water in impoundments is also influenced by the climatic conditions of different regions. Seasonal variations in the intensity of solar radiation coincide with the fluctuations in tempera- ture, thus providing the different optimum habitats needed for various development stages, and permit a series of species to become successively established in the water bodies. Regional winds cause wave and temporary currents in lakes, especially in shallow lakes, winds cause a constant mixing of the water of the whole depth, and this phenomenon results in a uniform distribution of oxygen, temperature, and nutrients in the water body. The frequency of rains in the area is also a major influence on water quality of the reservoirs. Rain drops not only engulf dust and absorb oxygen, carbon dioxide, and other organic substances while they are passing through the atmosphere, they also are contaminated with bacteria and other forms of organisms when they reach the ground. These waters enter reservoirs by runoff and stream flow, then become populated by aquatic micro-organisms, aquatic plants and other aquatic organisms. Morphometric Factors The quality of impounded water not only is affected by the type of reservoirs, its location and type of soils, and climate fluctuations. It is also affected by the morphometric characters of the reservoir itself. Larger surface area results in absorbing more energy from solar radia— tion, and thus higher temperatures. Greater area of shallow water results in higher productive potential. Mean depth is considered as a dominant influence on biological production in lakes and reservoirs. Rawson (1953) demonstrated that mean depth is inversely correlated with standing crops of plankton, benthos, and fish production. Reduction of mean velocity of water exerts in great effect on the population of bottom-dwellers as a result of heavy sedimentation. Slowing velocity also affects water temperature because of longer time exposure to the sun. This causes higher maximum water temperature in the reservoir than in its source (Curtis, 1960). Longer shoreline development results in more shallow water area, providing shelter and feeding ground for young fish and probably provides more spawning ground. Jenkins (1967) showed that increased shoreline development gave a higher total standing crap and sport harvest. PHYSICAL CHARACTERISTICS The quality of water stored in reservoirs varies greatly with physical environmental factors and time of year. Several physical factors of the water are altered following the completion of an impound— ment. Often the impounded water quality is better than that of the original stream. Irwin, Symons, and Robeck (1967) listed some positive effects of impoundment on improving water quality including: (1) blend- ing and diluting of influent water, with impounded water reduces the 10 effect of peak concentrations of pollutants; (2) detention and the lower velocity in the impoundment permit sedimentation and precipita- tion of solids; (3) exposing the water to light and air for longer periods permits greater biodegradation of organic wastes; and (4) higher trophic levels result from the transfer of energy to protoplasmic units during and following biodegradation. Light Penetration Light conditions in water differ from those in the air not only in intensity, but also in the depth of penetration of various parts of the spectrum into the water (Nikolsky, 1963). He pointed out that the coef— ficient of absorption of different wavelengths by the water is extremely variable. Within the range of visible light it absorbs the longer wave- length (from red) more effectively than it does the shorter (violet), whereas for those beyond the range of the visible spectrum, the shortest wavelength is the most effective in penetration as compared with light at surface of the water (Coker, 1954). The principal factors affecting the depth of light penetration in natural waters include density of suspended microscopic plants and animals, suspended mineral particles such as mineral silt, stains that impart a color, and detergent foams, or a combination of these (Mackenthun, Ingram, and Porgas, 1964). They also reported that the region in which light intensity is adequate for photosynthesis is often referred to as the trophogenic zone, the layer that absorbs 99 percent of the incident light, the depth may vary from 5 to 90 feet. The capability of light penetration in water also depends on the angle at which light strikes a water surface and thus amount reflected. Ridley (1970) reported that light penetration in a standing reservoir will be better than in the ll flowthrough reservoir because higher rate of sedimentation. This is also a reason for earlier algal bloom in standing reservoir and its tendency to persist much later into the fall. The significance of reduced light in an aquatic ecosystem is its becoming a limiting factor controlling the primary production in water. Stepanek (1960) has studied the relationship between solar radiation and primary production of nannophytoplankton in Sedlice Reservoir near Zeliv, Czechoslovakia. He found the production was significantly influenced by duration and seasonal variation of sunshine. He stated that the duration of sunshine was the most important factor influencing the production of nannophytoplankton. Even though the number of nanno- phytoplankters increased slowly with the increasing value of the duration of sunshine from 0 to 3.5 hours/day (100 to 1,000 cells/ml), the pulse of development (1,000 to 100,000 cells/ml) occurred corresponding to the increasing average period of sunshine above 3.5 hours up to the limit value (7 to 10 hours). Temperature The transfer of heat from the atmosphere to a body of water leads to an unequal distribution of temperatures, usually high temperature in the layers near surface and decreasing temperature with depth. The principal factors involved in the heating of lake waters include the absorption of solar energy, molecular thermal conduction, turbulent thermal conduction, and thermal advection into and out of the reservoir by inflows and discharges (Wunderlich and Elder, 1967). The absorption of solar energy and the distribution of absorbed energy are a function of the transmissibility of the water which varies with season and loca- tion. For example, during the day in summertime, the diurnal solar 12 radiation gives an increase of 2° to 5° F for the upper 10 feet. Such a temperature increment would lead to a high temperature within a rather short time if there were not a strong heat extraction by convective cooling during the night. In fact, the molecular thermal conductivity of water is very small; therefore, it is considered as a minor influence on the heating of large body of water compared with heat transfer caused by turbulent thermal conduction. This phenomenon includes the action of wind-induced currents and convectional currents resulting from surface cooling or bottom heating. Wind action causes several forms of heat transfer. During the daytime, warm surface water may be mixed into deeper layer by wind- induced turbulent diffusivity. If the wind persists long enough in the same direction, return currents caused by water pile-up on the down-wind shore may force the warm water into even deeper layers and bring cold water to the surface on the up-wind side. On the other hand, if the wind persists during the night, it increases the heat loss from the water surface; then, a vertical convective mixing in the water body may result. Heat transfer by thermal advection due to water inflow and outflow in most impoundments is a function not only of the flow rates, but also of the temporal distribution of temperature and density of the flows, depth, and volume relation, location and size of the outlet. As we all know, temperature has a controlling effect upon all forms of biological activity. The fluctuations in water temperature affect all living organisms in many ways including metabolic rate, feeding, reproduction, development, migration, and distribution of species (Rounsefell and Everhart, 1953; Zhadin and Gerd, 1961; Mihursky and Kennedy, 1967). The amplitude of temperature effects varies 13 considerably from one species to another. Within the limits of.tempera- ture tolerance for a given species, a rise in temperature usually leads to an increase in all physiological activity of fish (Nikolsky, 1963). Above the optimum level, temperature inactivates enzyme activity and results in a rapid decline in overall activity and ultimately, in death (Hawkes, 1969). Aquatic organisms are generally sensitive to high temperature. The ranges of tolerance are varied among different organisms and even of different stages of the same species. Organisms that tolerate a wide range of temperature are said to be eurythermal, and those with a narrow range, stenothermal. Hawkes (1969) gave an example of salmonid eggs having much lower upper thermal limits than the newly hatched alevins. Brett (1960) emphsized that tolerance ranges for the Pacific salmon are different at various stages of life history. The survival range of the eggs is narrower, especially during the hatching process (5.7—15.0° C), than the other life history stages. Range for growth (5.0-18.6° C) is also narrower than that for survival (2.5-25.l° C). These temperature requirements are important in determining the distribution of organisms in an aquatic ecosystem. The European Inland Fisheries Advisory Commission (1969) reported that temperature not only affects the development of parasites and pathogenic bacteria, it may also affect the resistance of fish to disease by affecting antibody production. Ordal and Pacha (1963) pointed out that most fish diseases are favored by increases in water temperature, such as kidney disease, furunculosis, vibrio disease on salmonid fish, and culumnaris disease in young fish. Furthermore, they also found many diseases prefer low temperature, such as those caused by an aquatic myxobacterium named Cgtophaga psychrophila; the disease is Itfiu ‘u- a C‘ 5‘ .- ' 01 8?. .4.“ .r‘. .C a. la V; .r . ’\ vflk \ . o s .u\ \ .J ‘u . l T. .. T "a E t .a C «J 7 2.. a. 16 . ..= a ..s t l T, . . n c n. . u .u .3 . A. c c ‘ \. €.\ A . .5 I; .1 .1 _. c S A e A . .. . c (a 2 w. .WM m MAW n. my a. s“ v . .l ..\ a§e 5s 9‘ t C L l4 referred to as "low temperature disease" or ”cold water disease." This disease is generally found in young silver salmon in the early spring, when water temperature is low, and in some outbreaks causes a heavy loss of young fish. When water temperature increases in late spring to summer this disease is self-limiting and disappears. The foregoing account demonstrates the importance of temperature as an ecological factor not only affecting the activity, distribution, incidence and abundance of aquatic organisms, it also has marked effects on the abiotic conditions, In nature, there are diurnal as well as annual fluctuations. These fluctuations are caused by the intense warming of the water by the sun in daytime and a considerable cooling of water during the night. In lakes, during daytime in summer, the upper layer (epilimnion) is greatly warmed, there is a sharp temperature drop in the intermediate layer (thermocline or metalimnion), and a constant low temperature in the lower layer (hypolimnion). In winter the reverse is observed, the bottom of the lake is the warmest, and the surface, the coldest. In spring and fall the temperature of lake water becomes uni- form at all depths (Zhadin and Gerd, 1961). The temperature gradient in a reservoir is almost the same type as that in natural lake. Except, the main source of energy to heat the water does not only come from solar radiation and the exchange between the reservoir surface and the atmosphere, it also depends on temperature of the inflows into the impoundment. Sylvester (1963) cited several factors that influence water temperature in impoundments, including: (1) volume of water impounded in relation to mean stremflow; (2) surface area of impounded water; (3) depth of impounded water; (4) orientation with prevailing wind direction; (5) shading afforded; (6) elevation of impoundment; (7) temperature of inflow water in relation to temperature 15 of impounded water. Unfortunately, he did net discuss these factors in detail. Thermal Stratification Water has a unique property of reaching its maximum density at 4° C (39.2° F); then it becomes lighter as it cools or warms. This property leads to vertical circulation in impoundments which is termed fall and spring overturn. As the season advances and the atmospheric temperature becomes higher, both inflowing water and the surface water of the impoundment get warmer. It then becomes more resistant to mixing, and a thermal stratification develops. Thermal stratifications in reser- voirs may develop along different patterns, depending on geographical location, climatic conditions, depth, surface area, type of dam structure, outlet design, reservoir operation, and hydrology of the drainage basin (Kittrell, 1965; Mackenthun and Ingram, 1967; Wunderlich and Elder, 1967; Posey and DeWitt, 1970). In the temperate latitudes, reservoirs of moderate or great depth ‘develop thermal stratification in spring or early summer, and in very shallow reservoirs the wind keeps the entire water mass mixed. On the other hand, in equatorial regions reservoirs of great area with moderate or shallow depth located in windy regions of low humidity, or at great altitude, there is no persistent thermal stratification developed. In contrast with reservoirs of small or moderate area or of very great depth, or in regions of high humidity, a very small temperature difference between surface and bottom suffices to maintain a stable stratification. A circulation may develop at very rare irregular intervals whenever abnormal cold spells occur (Hutchinson, 1957). 16 Several types of thermal stratification developed in reservoirs are well described by Mackenthun, Ingram and Porgas (1964) and Kittrell (1965). The simplest type is that developed in mainstream reservoirs, which occurs most frequently in warm weather as illustrated in Figure 1. This type of thermal stratification often consists of a small but fairly regular temperature gradient such as through the range of 25° C to 20° C decreasing from top to bottom during the summer. This phe- nomenon is most likely to occur in a reservoir with limited surface area where the wind action is moderate and velocities are low. A temporary thermocline has been recorded (Mackenthun and Ingram, 1964) where the temperature gradient is steep through a rather narrow band of water. Another type of thermal stratification in mainstream reservoirs involves the inflow of a tributary that is colder than impounded water surface. Kittrell (1965) indicated that it develops only when the water flows through a reservoir at appreciable velocities and requires large portions of the cross sectional area of the reservoir for passage, as illustrated in Figure 2. DAM DAM 25° C epilimnion 24° C «— inflow 23° C underflow 20°C 22° c ‘ ::;nfinaLQ£k___ 21° C '_ penstock intake intake \. \ —-20° Figure 1. Summer strati- Figure 2. Current tilted fication in mainstream reservoir. thermocline in mainstream reservoir. (From F. W. Kittrell, 1965) 17 The incoming water at 20° C is about 6* C colder than normal surface water during midsummer. The flowing water occupies the entire cross sectional areas of the upper end of the reservoir. Since the penstock intake (discharge) may extend from near the bottom to within 15 to 20 feet of the water surface, from about the middle of the reservoir on downstream, the cold water flows underneath the warm impounded water. Above the top of the penstock intake is occupied by a wedge shaped body of warmer water, consisting of a thermocline and an epilimnion. This type of thermocline is not horizontal, but is approximately parallel to the bottom slope of the impoundment and is held in this position by the cooler water flowing beneath it. Thermocline becomes more nearly hori- zontal when flow decreases. Greatly increased flow may completely eliminate the thermocline. The characteristic thermal stratification that develops in the storage reservoirs is much more complex than the simple thermal gradient pattern found in mainstream reservoirs. This type of stratification results in dividing the water column into three layers of the epilimnion, thermocline, and hypolimnion. In the United States, the summer strati- fication may occur as early as April in the southern states, and a month to six weeks later in the north. Figure 3 shsws the pattern of summer stratification in storage reservoir as a result of difference in water temperature gradient. The epilimnion has a uniform temperature of 26° C, below the epilimnion is the thermocline, where temperature decreases from 26° C at the top to 10° C at the bottom of the stratum, whereas temperature of the hypolimnion is 10° C at the top and 8° C at the bottom. A period of summer stratification may persist until late October or early November in the south, and may terminate a month or so earlier in the north. 18 During the summer stratification period, the hypolimnion is unable to replenish its dissolved oxygen and the decomposition of organic matter at the bottom depletes the available oxygen. demand is sufficient, the hypolimnion may become anaerobic. If the oxygen This con— dition may result in producing hydrogen sulfide, increasing color, and the iron and manganese content of the water may reach the objectionable level (Kittrell, 1965). DAM ¢——- inflow O :ETZOC 25°C iO‘C 9°C / .n——.penstock \ intake —'8°C Figure 3. fication in stor (From F. W. Kittrell, 1965) Summer strati- age reservoir. Storage reservoirs that do not store substantial volumes of water at winter temperature or that discharge such water before warm weather occurs do not develop a thermocline; neither do shallow reservoirs with broad eXpanses of surface area exposed to strong winds. In the fall, following summer stratification, the temperature drops, cooling continues until temperatures and densities of the epilimnion and thermocline approach those of the hypolimnion. Then, 19 the resistance to mixing is reduced, wind induces mixing and temperature becomes uniform from top to bottom. This is known as the "fall overturn." In the temperate region, stratification may be developed during winter, wherever temperature drops as low as 0° C, and especially where ice cover forms (Kittrell, 1965). He described a temperature pattern of winter stratification which is the reverse of that in summer as shown in Figure 4. The colder water at 0° C is at the surface, below the ice cover, while warmer water is deeper. The temperature increases sharply from 0° C to 4° C in the surface stratum, and resembles an inverse thermocline. On the other hand, for those regions where surface water temperature rarely drops below 4° C, there is no stratification in winter. Temperature is nearly uniform throughout the water column. DAM ice "— 2 C 30C .— inflow 4° C Temperature 4° C /’ sodb‘ '“, «v- y- {c \U l d] e 4..“ o, .o . w“ “A .V\§_ ‘ uAAOm ‘J r& t q A I. s . . . O . r 1 1 t l .m . . . 9 as v p n I q i _: .l C F 3. a. . . . v . L“ .1 Au . . .t n u .3 a . . E E .n . . h . 6 Mi r A... e w. ‘ a . a v a >u J 4 «W . . .C o» C i“. E : .C D. E E. .3 i. o 5 “t C. n . .3 A ‘ a v. 3» RM 2; 4 . e .C v. 0 a Fk . . v . "a. s . .3 I A u :5 s . IR . r I... 3113, .‘I‘ 21 As a result of exhausting the oxygen supply in the hypolimnion, several reactions take place; iron and manganese are reduced and go into solution; sulphates are reduced; odorous and toxic hydrogen sulfide is formed; excess carbon dioxide is created; hydrogen-ion concentration of water is lowered; and aerobic degradation of organic material ceases (Symons, Carwell, and Robeck, 1970; Symons, Echelberger, and others, 1971). Artificial Destratification In order to control quality of water, attention has been concen- trated on treatment facilities for improving water quality in lakes and reservoirs. Several possible designs have been extensively reviewed by Kittrell (1965). Among those techniques, artificial destratification is considered as an effective method for water quality improvement, since it has the double benefit of improving water quality in the reservoir itself as well as protecting downstream quality. The principle of artificial destratification is the destruction of density layering of the water column or the reduction of temperature gradient to allow the hypolimnion water to mix with the epilimnion water to prevent anaerobic conditions in the bottom layers. Currently, only 4 methods are employed for the artificial destratification: mechanical pumping; diffused air-pumping; perforated aeration tubing; and the Aero—hydraulic Gun (Symons, Irwin, Clark, and Robeck, 1969; Ridley and Symons, 1972). 1). Mechanical Pumping. This method involves mechanical pumping of cold water from the bottom of a stratified water body and discharging at the surface. The apparatus uses a 12 inch mixed flow pump driven by a 16-hp gasoline engine on a raft. The raft is stationed over the l . . . . . -. u e o a .n :C 3 -i 3 .2 L C . i E S L. .. . T . 9L an 2,. vi a .C is f? h. t .6 Ad . 4 a .n L: r; .1 t; C v. :. . i .3 . C. r e y. 2. Z 3 s. C e .. .. .. .2. Q ... .... L C L.. Cs e» e; u“ l .u E .t v; a}. e s a J; F. e» «1. f. 5 5L t .b C. .3 .A YL 1K. ~r~ C ad 22 deepest part of the lake. Water is drawn through a suction pipe, 1 or 2 ft off the bottom (Symons, Carswell, and Robeck, 1970). 2). The Diffused-Air Pumping. The equipment used for this opera- tion is a 22.4 kw/hr/portable air compressor that delivers about 115 cfm air at about 30 to 40 psi. The air is released through 16 porous ceramic diffusers spaced at 3 ft intervals in a cross pattern. This gives a cylinder of rising air, approximately 4 ft in diameter, that increases to about 100 ft in diameter at the surface (Symons, Carswell, and Robeck, 1970). 3). The Perforated Aeration Tubing. This method requires 1,500 cu.ft/min. of air delivered by various small compressors. Air would be supplied continuously and released through thousands of special die- formed check valves, resulting in a slow rise of pinpoint bubbles to the surface. The introduction of oxygen would change the water density of the hypolimnion sufficiently to cause vertically mixing of all strata in the reservoir. Tests were cited as having been successful at a 3,800 acre-ft lake in Warsaw, Indiana, using only 5-hp energy input (Posey and DeWitt, 1970). 4). The Air-Hydraulic Gun. A device manufactured by Aero—Hydraulics, Limited, which is sometimes called Aero-Hydraulic Gun but is popularly known as the "Bubble Gun" (Irwin, Symons, and Robeck, 1969). This method was used for destratification of the West Point Reservoir, Georgia, by Posey and DeWitt in 19700 This reservoir has a surface area of 25,900 acres and a storage of 604,500 acre-ft of water. The manufacturer of a patented hydraulic air-gun system proposed using 30 of his units to improve the quality of water. Each gun is 25 ft in 23 length and 12 inches in diameter. The design is based on a polyethylene stack pipe with an air distributor at the bottom end. A large air bubble is formed which acts as a piston as it rises up through the pipe. The air bubble eXpands as it leaves the pipe muzzle, and in effect lifts the lower level water to the reservoir surface sufficiently to cause vertical circulation in the reservoir. The effectiveness of these methods for artificial destratification of lakes and reservoirs can be evaluated by the calculation of the "oxygenation capacity" and "destratification efficiency." Symons and Robeck (1969) and Ridley and Symons (1972) have defined these two terms by the following equations: Net change in oxygen balance from t1 to t2 X hypolimnion volume in billion gallons Oxygenation capacity (CC) = Total energy input from t1 to t2 where: t1 = time of start of mixing t2 = time of end of mixing Oxygen balance = {DO+(-SO'§)+(-Fe02‘H')-l-(-Mn02'H')} D0 = pounds of dissolved oxygen per million gallons below thermocline SO§ = pounds of oxygen equivalent to sulfide (conc.XZ) per million gallons below thermocline FeOz++ = pounds of oxygen equivalent of reduced iron (conc.X0.29) per million galons below thermo- cline Mn02++ = pounds of oxygen equivalent of reduced manganese (conc.X0.29) per million gallons below thermo— cline CC = pounds of DO transferred per kilowatt-hour They recommended that a convenient method of calculating the oxygen balance is dividing the hypolimnion into 5- or lO-ft vertical sections and using the volume and chemical analysis for each layer. 24 When this technique is used to compare various methods, presumably the one with highest oxygenation capacity would be the best. Symons, Irwin, and Robeck (1969) suggested that whenever this parameter is used, for a fair comparison the following should be kept in mind: (1) the oxygenation capacity value is inversely related to the oxygen balance that exists at the start of a given test, usually the oxygen balance is higher than the oxygen capacity; (2) the time rate of change of oxygen balance during a given mixing as dissolved oxygen saturation is approached the length of a test influences the resulting oxygen capacity; (3) a control is needed to determine how the oxygen balance would have behaved had there been no mixing; and (4) because meteorological conditions may vary from test to test, comparison should be made under similar meteoro- logical conditions. Net change of stability from t1 to t2 = X 100 Total energy input from t1 to t2 Destratification efficiency (DE) where: t1 = time of start of mixing t2 = time of end of mixing stability = minimum energy needed to completely mix a lake to an isothermal condition The mechanical device with the highest destratification efficiency would also have the best re-aeration characteristics, and would be the best device for use in a given reservoir. However, using the destratification efficiency technique for com- parison of various destratification methods is difficult and may not be correct for design purposes because there are several factors influencing its effectiveness as listed by Symons, Irwin, and Robeck (1969). These factors are: (l) the rate of change of stability with respect to time declines as the mixing operation proceeds; (2) morphological differences rq'l'V'" .yn.tb- 9“ VJ. -Q .0! f \ ““OII 3.4 a. ] 0.5 c I 4 fl. . 4 . r. t C P. r .: .: C 3i 9 a C .c E .C 3 E i z . a r. a .a . c C a a.» v a ks . v . 7r my .n a. m. a _ . ; c ., t mu Ci .3 ‘c .J. n. . m . ..r . .. . M 25 affect the calculation of stability such as, a large surface area with respect to the total volume will develop stability much faster than a lake with a small surface area with respect to total volume; (3) a control is needed to determine what the cause of the calculated stability would have been in the body of water under study if there had been no mixing; and (4) the test should be made under similar meteorological conditions if possible. Several conditions develop in reservoirs following artificial destratification. Symons (1969) has summarized the influence of destrati- fication on the water quality in lakes and reservoirs as follows: 1). Artificial destratification with some mechanical device is an effective method of improving water quality in reservoirs or maintaining good quality of water in reservoirs, or both. 2). Artificial destratification creates a uniform temperature throughout the reservoir depth, adds D0 to the water, oxidizes reduced materials such as sulfide, iron, and managanese, or prevents their formation, but does not impair the clarity of the water. 3). Although some nitrogen and phosphorus may be brought to the surface during artificial destratification, increased algal populations do not occur. Actually, because of some environmental change, the algal pOpulations temporarily decline during artificial destratification. Usually, the blue—green algae decline more than the green algae. 4). The decline in plankton during artificial destratification is only temporary, as the population rises again after mixing stops, but not to bloom levels. Evaporation Evaporation is a continuous process in which water is transformed into the gaseous state and released into the atmosphere. In nature, the 26 sun is the most important source of energy for this transformation. Sylvester (1963) stated that the original source of energy for evapora- tion is solar radiation which is divided into three parts: direct solar radiation; heat that reaches the evaporating surface from the air; and heat that is stored in the evaporating body. A report of the Task Group for Evaporation Control (1963) indicated that during the summer, the main factor affecting evaporation is solar radiation, but in winter it is the stored energy in the water itself. In addition to solar radiation, evaporation also depends upon several factors, including air and water temperatures, relative humidity, wind movement, surface area, seasonal variation, location and topography of the water body. Margin and Randall (1960) reported that high temperature increases loss; dry air absorbs moisture more readily than moist air; a greater wind move- ment carries off more vapor; and the larger the area, the greater the loss by evaporation. Meyers (1962) found evaporation from the enlarged water surface of a new reservoir or lake is usually much greater than the evaporation under original stream condition. In Australia, Haunam (1963) reported the average values of evapora- tion in summer are five times greater than in winter. In some regions, the loss of water from the surface often exceeds the amount of precipi- tation falling on it. For instance, the amount lost by evaporation of Lake Sevan, Soviet Union, is twice as much as of the annual precipitation on its surface (Drachev, Amrin, and Bylinkina, 1966). They also reported the loss of water from the surface of the Aswan Reservoir in Egypt is about one-tenth of its capacity annually. Meyers (1972) estimated annual loss from the surface of streams and impoundments in the seventeen western states of the United States at 23,641,000 acre-ft. The evapora- tion from the surface of rivers and reservoirs in Turkmenia, the USSR, 27 in 1960 amounted to 10 percent (cubic meter) of the total water utilized for the national economy (Drachev, Amrin, and Bylinkina, 1966). Evaporation not only causes direct loss of water from the surface, it also causes the deterioration in water quality owing to the increase of salt concentration and suspended materials. Heat is used during water transformation, therefore decreasing temperature results at the water surface. These changes may influence several water quality parameters which probably reduce its utilization and productive poten- tial; therefore, much research deals with methods for reducing the evaporation. Several techniques have been employed to reduce evapora- tion loss. Most procedures consist of reducing the water surface exposed to the atmosphere. A summary of these methods is based on the works of Mansfield (1963), Task Group for Evaporation Control (1963), and Frenkiel (1965) as follows: 1). Locating Reservoir. Site location is perhaps the most important factor influencing evaporation from a reservoir. There is increasing evidence that higher altitude reservoirs lose less water per unit surface area than do reservoirs in lower altitude. 2). Shaping_the Reservoir for the Lowest Surface Area/Volume Ratio. The surface area can be reduced by constructing reservoirs with maXimum depth for a given volume. This includes both the choosing of a site with steep banks and diking-off shallow areas. 3). Reservoir Regulation. In a reservoir and river system consist- ing of both high altitude and low altitude reservoirs, it might be possible to operate the system in a way to present the least exposed surface, for the system as a whole, during the season of high evapora- tion loss. 28 4). Covers. These include floating covers, consisting of reflec- tive materials such as polyethylene films and floating covers of rigid plastic. The use of polyethylene films in stock pond tests has shown that the material becomes inundated by the weight of dirt and dust deposited on it, while solid plastic covers are similarly impracticable for large storages and interfere with gaseous interexchange with atmosphere. 5). Windbreaks. The effective windbreaks must present a dense barrier from the ground level. Vegetative windbreaks will involve evapotranspirational losses which will have to be subtracted from whatever evaporation savings may result by reduction of evaporation loss from the reservoir. 6). Air—bubbling. For deep reservoirs where a considerable pro- portion of the water in storage remains cold throughout the year, the air—bubbling technique might be practical. The technique consists essentially in bubbling air from the bottom of the reservoir to arti- ficially mix the water and break up the stratification. In this way colder water rises to the surface and the evaporation is thereby reduced. 7). Monolayer-Film Formation. A number of substances have the ability to form monolayer-films, a film only one molecule thick when properly spread over another substance. An important factor for the effectiveness of evaporation depressants is the presence of insoluble particles on the surface of the reservoirs. Normal hexadecanol and normal octadecanol are the two chemicals that meet most effectively the conflicting requirement of an evaporation suppressant for field use. 29 Because they are edible, tasteless, odorless, no harmful effect has been found to bird, fish, animal or plant life whenever used in the concentrations and in the manner appropriate for evaporation control. They also do not alter the potability, mineral content, taste, odor, or color of the water (Task Group for Evaporation Control, 1963). In general, investigations confirm the usefulness of evaporation depressants, which usually reduce the evaporation by 20-30 percent, compared with controls (Drachev, Amrin, and Bylinkina, 1966). However, many of the technical problems in using evaporation depressants, includ- ing the optimum conditions for their application and economic aspects, need further study. Furthermore, withdrawing warm water from the surface instead of cold water at some depth could substantially reduce evaporation from a reservoir (Harbeck, 1958). He assumed that when the withdrawals are made at the surface, temperature of water surface will be decreased, thereby decreasing the amount of evaporation. He showed the decrease of 8 percent evaporation from Lake Mead as a result of the water surface withdrawals. Turbidity Mackenthun and Ingram (1967) stated that "Turbidity is an expres- sion of the optical property of water that causes light rays to be scattered and absorbed rather than transmitted in straight lines." Turbidity is caused by a variety suspended particulate matter, such as living or dead phytoplankton or zooplankton cells, algae, bacteria, protozoans, small crustaceans, including silt or other finely divided inorganic and organic materials. Brown and Ritter (1971) reported that during the drier months of the year when runoff is low, turbidity in 30 the streams and reservoirs of the Eel River basin is caused primarily by the presence of phytoplankton and other micro—organisms. During the rainy months when water runoff is high, suspended sediment is the chief cause of turbidity. Reid (1961) classified suspended matters in reservoir into 2 groups—-one produced outside and brought into the lake called "allochthonous" and another produced within the reservoir called "autochthonous." Both contribute to the total quantity and quality of impoundment turbidity. Several methods for measuring turbidity have been advised. Welch (1948) grouped them into 3 classes: (1) comparison with silica standards; (2) platinum wire method; and (3) turbidimetric methods. Recently, Eden (1965) recommended 3 methods for use in turbidity measurement: (1) nephe- lometry--the assessment of the intensity of scattered light as a propor- tion of the incident light; (2) turbidimetry--the measurement of the ratio of the intensity of the transmitted light to that of the incident light; and (3) measurement of the depth at which a target ceases to be visible to an observer at the surface because of combination of absorp- tion and scattering effects (extinction effect). He also listed the instruments used for this purpose including (1) visual comparison of samples of the water in clear glass bottles with standards; (ii) the Jackson candle turbidimeter; (iii) Peterson turbidimeter; (iv) photo- electric measurement of optical density; and (v) photoelectric measure- ment of the light scatter. The standard unit for measuring turbidity is that condition produced by one part per million of silica (fuller's earth) in distilled water. Turbidity causes several problems in the water body. It may limit the use of water for public consumption or make it unsatisfactory for recreational uses. The effect of suspended substances entering the 31 water body is two-fold; if favorable it increases the biological pro- ductivity of the water body, but the mineral suspensions and the excess organic matter may have adverse effect (Zhadin and Gerd, 1961). As the suspensions make the water turbid, they limit light penetration into the water which restricts the growth of attached bottom plants, as well as suspended algae. Also, solids may floculate planktonic algae and animals and carry them to the bottom to die. Then they consume con- siderable amounts of oxygen in their decomposition process and free carbon dioxide is produced. The suspension of particles in the water has various effects upon fish. Fish of turbid rivers show a reduction in the size of the.eye to reduce the unprotected surfaces which could be damaged by the suspended particles carried by the current (Nikolsky, 1963). At hight turbidity levels, Buck (1956a) found the growth and total yield of bass and blue- gill decreased, but increased channel catfish production. The number of species as well as individuals of all scaled fish was low in turbid Heyburn Reservoir (1,070 acres), apparently due to lack of successful reproduction in the turbid waters and also to the competition from better adapted catfish. Furthermore, stratification in lakes and reservoirs may develop as a result of difference in turbidity as well as temperature. This is known as turbidity currents or density current. Because turbid water is denser than clear water of the same temperature and salinity, there- fore it plunges beneath the mass of clear water and flows through it. In some cases the density of turbid river water entering an impoundment is greater than density of the upper layers but not as great as the density of lower strata; under this condition the inflows sink beneath the lake surface and flow on one of the lower water layers of higher 32 density. Moreover, the muddy river water may flow over the lake surface whenever the sediment-laden river is warmer or less saline, or both, than the underlying water. Gould (1960) had studied the turbidity currents of the Boulder Basin and Hoover Dam. He reported that the turbidity currents are always present near the mouth of the Colorado River, but only rarely does it flow the entire length of the lake. The three types of currents mentioned above as overflow, interflow, and underflow all occur in Lake Mead. The overflows found occur only during late spring and early summer (usually from late April to early July) when the incoming river water is less dense than the surface of the lake, because of lower salinity than that of the lake water. During the summer, temperatures of the river and the lake surface were about the same, but the salinity of the incoming water was considerably greater than the salinity of the lake surface layer. At this time, the density of the river water even with its dissolved and suspended load was not as great as that of the colder water at the bottom of the lake; therefore an interflow developed. In late spring and summer, overflows and interflows are periodically replaced by underflows, and once again between fall and winter. The water discharged by the Colorado River from October to April is colder and more saline than deep water in the eastern part of the lake. Owing to these factors and to its suspended sediment, the muddy river water sinks rapidly beneath the clear lake water and travels along the submerged Colorado River channel. However, most of the turbidity currents that were observed to reach the western part of Lake Mead occurred during the first 7 years of the reservoir operation (1935-1941), when the lake was 70 to 120 miles long. The only major flow of turbid water to reach the dam since 1941 arrived 33 in the fall of 1947, when the distance between the river mouth and the dam was about 78 miles (Gould, 1960). Sedimentation The accumulation of sediment in reservoirs has long been recognized as one of the principal problems involved in reservoir management. The provision for sediment storage is the major consideration in the planning, selecting and design of a reservoir project for estimating the useful life of the proposed reservoir. The life expectancy of the reservoir is progressively reduced, along with its economic value, depending upon the rate of sediment accumulation. For an example, Gould (1960) reported the water storage capacity of Lake Mead, the largest man-made lake in the United States, at the level below the permanent spillway crest (1,205.40 ft elevation) was 27,376,000 acre-ft in 1948, a decrease of 4.9 percent in 14 years. If the rate of sedimentation is assumed to be constant, the maximum eXpectancy of Lake Mead would only be about 280 years. The problem of determining the useful life of a reservoir is not a simple one. It is complicated by the fact that sedimentations are governed by numerous variable factors which include sediment quantities and characteristics; reservoir size and shape; tributary locations and relative magnitudes of sediment contributions; unpredictable sequences of extremes of hydrologic events and effects of coincidental regulation operations; influences of unforeseen upstream developments and climate (Gottschalk, 1948; Maddock, 1960; Pais-Cuddou and Rawal, 1969; Paulet, Kohnke, and Lund, 1972). However, the life of a reservoir may be predicted if rate of sediment movement into reservoir is known. Pais— Cuddou and Rawal (1969) suggested that rate of sediment deposition can 34 be determined in two ways: (1) by measurement of inflow and outflow sediment; and (2) by conducting the actual capacity surveys of the reservoir by Echo-sounding instruments. They also recommended the latter method as comparatively more accurate and the results obtained are well within 10 percent of the true value. The amount of sediment may be expressed in terms of either volume or weight. Gould (1960) defined the sediment volume as the space occupied by the accumulated material, which includes both the solid constituents and the intersti- tial water; while the sediment weight includes only the solid particles. The easiest and most practical method of computing the volume of sedi- ment deposited in a reservoir between certain survey dates is by determining the difference in capacities of the two dates (Heinemann and Dvorak, 1963). The maximum life of the reservoir will be considerably greater than the calculated result because the rate of storage depletion could not be expected to remain constant, even with a uniform rate of inflow sediment, owing to the progressive compaction of the accumulated sedi- ment. Also, the sediment storage capacity is considerably greater than the water storage capacity of the reservoir because the upper surface of water must be essentially horizontal but the sediment surface must slope upstream from the dam (Gould, 1960). He demonstrated that the difference between the water—storage and sediment-storage capacities of Lake Mead is equal to the volume between the level surface at the eleva- tion of the permanent spillway crest and the sloping sediment surface that will extend upstream from the dam when the reservoir becomes filled with sediment (Figure 5). Prolonging the life of a reservoir may be done by reducing the rate of sediment contribution to the reservoir through soil erosion and 35 CNN A83 .vaaoo aoumv .Hm>mH mmaaaamm uaooqauoe ou voaaam ma mama «nu oun3.vmoz mama aw umuaaaaauou on vases umnu unmawvmm mnu mo uomwuom msu mo coauMunmmoummu ofiumaamuwmfia hunch moon scams mafia: o¢~ com owN com omm own — _ r. P _ L mmma ca mHHwoue uw>fim owmuoaoo 3H w>mH mmaaafiam m>onm mwmuoum unmafiva now manmafim>m momam um «.moma .umwuo zmzaafiam uaoamapmm mo coaum>wam mommusm unmafivmm wouomhoum .m «human coo .. o2 o8 .. com r coo A . 2: .H . com 4 A: oom.H 00¢.H nae; u; uornenatg H. - n“?“‘ A bad. a L DEZLZE 36 watershed controls, or by moving some of the sediment out of the reser- voir through the withdrawal operations (Maddock, 1960). The influences of sedimentation on water quality involve the relations between sediment and the physical, chemical, and biological characteristics of the water. The Task Committee Assigned to Inventory Sedimentation Research Needs Related to Water Quality of Hydraulics Division, ASCE (1971) has summarized all the effects of sedimentation on water quality as follows: 1). Sediments provide large surface areas where chemical reactions may occur. Such reactions (adsorption, absorption, desorption) may contribute to more rapid detoxification, and degradation of many pollutants. 2). Sediments interfere with fish or shellfish by smothering effects on adult, young, or eggs. Silt or other deposits destroy spawning grounds for fish and eliminate clams and oysters. Destruction of small organisms such as crustaceans and algae can seriously affect larger organisms that depend on them for food. Much more can be done to identify adverse effects on fish or shellfish by both biological and chemical studies. 3). Suspended sediment restricts penetration of light, turbidity tends to inhibit growth of phytoplankton and other algae which might assume nuisance proportions. On the other hand, turbidity frequently results from resuspension of bottom sediments by waves, currents, or organism activities. Under such conditions they often have a stimula- tory effect on algal growth by effecting a sediment to water nutrient interchange. 4). The sediments of lakes and reservoirs typically contain high concentrations of nitrogen, phosphorus and other plant nutrients. If C 1 i i 37 significant releases of these nutrients from the sediments to the over- lying water occur, and if these nutrients become available within the photosynthetic region of water, growth of phytoplankton can be stimulated. Sediments may actually decrease rate of eutrOphication in reser- voirs or lakes. Rapid sedimentation will bring in inorganic as well as organic material and may cover the organic sediments thus limiting nutrient exchange between the sediments and the overlying water. Slow runoff can, on the other hand, reduce sedimentation but also supply nutrients by leaching from the soil. The role that sediments play in the nutrient cycle needs clarification. It seems provable that bottom sediments are highly important in removing oxygen from the hypolimnion of a thermally stratified lake due to oxygen uptake by organic sediments, decompositions by fungi, benthic algae, and bacterial attack. Sisler (1960) reported that bacteria may influence the mass of sedimentary material in many ways. They may produce or destroy or alter the reaction of the sediments, which may increase or decrease the bulk of sediments. The reaction may bring about the solution of carbonates or may even result in the evolution of gaseous carbon dioxide. The solution of biochemically unstable substances, such as organic matter, carbonates, sulfates, nitrates, iron, and other metal compounds, may be produced directly or indirectly through the influence of micro-organisms. Water-Level Fluctuations Most reservoirs are characterized by fluctuations of water level which are associated with economic importancy--for energy production, irrigation, navigation, and flood control. These fluctuations, of 38 course, vary greatly in degree and pattern from one impoundment to another, or within the same impoundment from year to year. The manipu- lation of water—level fluctuations in a reservoir is a valuable tool in managing the fishery resources. Wood (1951) suggested that manage- ment of water levels to alternately expose and flood bottom soils is significant in maintaining the productivity and increasing fishing success of large impoundments. He stated a mid—summer drawdown would permit the invasion of vegetation into the zone of fluctuation. Raising water levels in the fall would prevent erosion of the shores of an impoundment and maintain the productivity of shallow waters, and provide habitat for an abundance of fish-food organisms. Species dominance and relative abundance of predatory, forage, game and rough fishes in lakes and reservoirs were also influenced by water—level fluctuations (Wood and Pfitzer, 1960). For example, the winter drawdown of 70 ft or more of the Norris Reservoir has greatly reduced the edible forage species such as carp and buffalofishes with a corresponding increase in gizzard shad or other non—edible forage species, comprising about 70 percent by weight of the samples. Summer drawdowns were found more effective in preventing spawning of sunfish and shad and may have a depressant effect on the predatory fish pOpulations by decreasing the amount of forage fish of desirable size in the spring (Lantz, Davis, Hughes, and Schafer, 1964). In Sweden, Runnstrom (1960) reported that changes in water-level in impoundments will influence the reproduction of fish through the loss of places for spawning and development of the young. The same effect happens with several species of bottom fauna and larvae of insects, resulting in a reduction in food supply for the fish. an: an. a y rrw SI. “3‘ .v e. P ~. e had (1v 5 u-IQ a L . v TL . g ”A.“ .VJ t ‘m I|\ d V) a £4 39 In the Soviet Union, Zhadin and Gerd (1961) noted that fluctua- tions of water-level in reservoirs may either decrease or increase the food supply for the fish. The decline of water-level is lethal to many bottom dwellers including molluscs, bryozoans, spongs, larvae of gnats and other clinging insects, and some crustaceans, but the drained over- grown meadow and swamp vegetation will die and transform into organic manure when flooded again. Their decomposition will provide ample bacterial food for midge larvae and other invertebrates thus increasing the amount of organisms serving as fish food. The use of water fluctuations in controlling aquatic plants in lakes and reservoirs is recommended by many investigators. Runnstrom (1960) noted that higher water-level in the summer and the drainage during the winter of Swedish lakes cause the disappearance of aquatic vegetation, while in the United States after the summer drawdown, the aquatic vegetation problems such as pondweed, water lily, parrot- feather, and water-shield had been greatly reduced (Lantz et al., 1964). In the tropical or subtropical regions, many reservoirs present serious malarial hazards to the adjacent human population in providing breeding places for the mosquito vectors of that disease. Small draw- downs made at frequent intervals during the mosquito season have been beneficial in partly controlling the mosquitos in the shallow portions of the impoundments (Ellis, 1941). It is apparent that the effects of water-level fluctuations in impoundments vary with time, area, and duration of flooding. Yet it is considered as one of the most effective tools in fishery management, but the practice is limited by conflicting with primary uses of the water stored in reservoirs such as hydro-electric power projects. 40 CHEMICAL CHARACTERIST IC S Water is often called a universal solvent. On contact, it dissolves several gases and solids in great variety and amount. The hydrochemical conditions of natural water differ from place to place and in various types of the water bodies. The chemical composition of natural water is derived from different sources of solutes, including gases and aerosols from the atmosphere, weathering and erosion of rocks and soils, solution or precipitation reactions occurring below the land surface, and cultural effects resulting from activities of man. The ways in which solutes are taken up or precipitated and the amounts present in solution are also influenced by several environmental factors, especially climate, structure and position of rock strata, and biochemical effects associated with life cycles of plants and animals, both microscopic and macroscopic (Hem, 1970). The chemical properties of water affect all the biological func- tions of aquatic organisms, determine the limits of their distribution, promote the development of some groups of plants and animals, and the suppression of others (Zhadin and Gerd, 1961). In contrast, aquatic organisms can influence the concentration of compounds directly by metabolic uptake, transformation, storage and release (Lee and Hoadley, 1967). Ox en Oxygen is one of the most significant factors in an aquatic eco- system. It is necessary to all living organisms in one form or another to maintain the metabolic processes that produce energy for growth and reproduction. It is the principal factor in natural self- purification of the water bodies. By nature, oxygen is a rather poorly 41 soluble gas. Its solubility varies inversely with temperature at any given atmospheric pressure. For example, at one atmosphere of pressure, the solubility in freshwater ranges from 14.6 ppm (mg/1) at 0° C to about 7 ppm at 35° C as shown in Figure 6 (Sawyer and McCarty, 1967). The concentration of dissolved salts inversely affects its solubility in the water (Odum, 1959). 204r L4 m U ;j 154. \ ED .5 10‘ >. U ~H r—4 :3 5s, a H 0 U) 0 l I T l I 47 5 10 15 20 25 30 35 Temperature °C Figure 6. Solubility of oxygen in distilled water saturated with air at 760 mm Hg. (From C. N. Sawyer and P. L. McCarty, 1967) In nature, the dynamics of the concentration of dissolved oxygen depends on the process of interchange of oxygen with the atmosphere (atmospheric aeration) and an oxygen production by aquatic plant photo- synthesis, on one hand, and is removed by respiration of organisms and decomposition, on the other (Mackenthun, 1969; Umnov, 1971). The dissolved oxygen structure of a reservoir is a primary consideration in water quality because the ecological balance in the impoundment is very sensitive to dissolved oxygen levels. The oxygen balance in a reservoir is dependent on water temperature, winds, duration of the ice cover, convective transport by interval currents, atmospheric aeration at the 42 surface, photosynthetic oxygen sources associated with plant life, oxygen demand of river inflows, bottom deposits, respiration and decomposition of aquatic organisms (Rutkovskii and Kireeva, 1957; Markofsky and Harleman, 1971). The variation of temperature gradients in a reservoir with time and distance from the water surface results in the development of thermal stratification. During this period, the epilimnion is usually abundant with dissolved oxygen which is supplied by atmospheric aera- tion and photosynthesis. The thermocline is a transition zone, incident light is much reduced, and photosynthesis is usually decreased. The concentrations of dissolved oxygen in this region decrease rapidly with depth. In the hypolimnion, dissolved oxygen may become depleted because the water is completely shut off from aeration; therefore, dissolved oxygen which is removed from the water both by respiration of organisms and decomposition of organic matters is not replaced. The effect of wind on aeration is the agitation process. Blowing of the wind may increase atmospheric pressure at the water surface and also decrease the water temperature at the surface of reservoirs. Decreasing temperature coinciding with higher pressure will increase the solubility of oxygen in water. Furthermore, if the wind blows in the same direction for a long period of time, circulation in the water bodies will result. The degree of circulation depends upon the wind velocity, blowing period, and area of open water surface in contact. Mixing of the water will facilitate the distribution of oxygen into deeper layers providing more dissolved oxygen for respiration and decomposition. However, the wind not only adds oxygen to the water, its action may also release dissolved oxygen under the conditions of supersaturation. 43 Hull (1965) stated that a significant factor in controlling the oxygen concentration of natural water is the photosynthesis by aquatic plants, including phytoplankton. Recently, Umnov (1971) made an assump- tion that the only source of photosynthetic aeration in the reservoir is phytoplankton, since in some impoundments rooted vegetation does not play an important role in primary production of organic matter. He also described the specific rate of photosynthesis of phytoplankton as increasing with temperature, attaining its maximum value within the certain range of optimal temperatures and then decreasing with further rise of temperature. Moreover, it is also known that specific rate of photosynthesis is reduced with the increased phytoplankton concen- tration (Figure 7). phytoplankton concentration rate of photosynthesi ‘1", //+ . «91%? ‘ tira/ I ) \ \, temperature Figure 7. Dependence of the specific rate of photo- synthesis on temperature and phytoplankton concentration. (From A. A. Umnov, 1971) The concentration of dissolved oxygen is strongly affected by quality of inflowing streams and groundwater. Streams that carried substantial amounts of organic matters will increase the biological oxygen demand above that already present in the reservoir. If the 44 requirement is great enough and there is a long retention period of impounded water, dissolved oxygen may be completely depleted by decompo- sition processes. On the other hand, if the inflows are clean and rich in dissolved oxygen, an increase in D0 of impounded water will result. In temperate regions, the presence of ice and snow at the surface of the water bodies will reduce the concentration of dissolved oxygen in the water. Under ice covered condition, the atmospheric aeration is absent and oxygen from photosynthesis by aquatic vegetation is limited. DecompOSing of organic matter removes oxygen from the water, as does respiration of aquatic organisms especially in the hypolimnion. If this condition remains for several months, a severe oxygen depletion may occur. However, winter stagnation in reservoirs of the northern United States does not result in total oxygen depletion in bottom waters owing to the high initial dissolved oxygen concentration, the low rate of oxygen demand, and the shorter period of stratification (Kittrell, 1958). Types of reservoirs exert an important effect on the dissolved oxygen resources of impounded water (Kittrell, 1958). He found the water of storage reservoirs contains higher dissolved oxygen concentra~ tions than mainstream reservoirs do, as a result of greater surface area and pro onged detention time of the storage reservoir. The area provides more atmospheric aeration at the water surface. Time probably provides more chance of circulation by wind action, and encourages increased production of algae, which add oxygen by photosynthesis. As a result, water flowing into the epilimnion of a storage reservoir soon approaches saturation with dissolved oxygen. Rutkoskii and Kireeva (1957) reported after filling of the reser- voirs, the concentration of dissolved oxygen is considerably decreased U... Bug‘s-fie. an. r... 7..» r. .. . a uni . 45 as a result of decomposition of flooded vegetation and other organic sediments. Mortimer (1971) found that a progressive decline in oxygen concentration from 2 ppm of oxygen at the bottom interface was accompanied by a fall in electrode potential in the upper layer (few millimeters) of sediment. This correlated with mobilization and transfer into water of iron and manganese and substantial quantities of phosphate. Other changes include liberation into the water of ammonia, silicate, and the reduction of sulfate. The decomposition of organic matter under anoxic conditions in Keystone Reservoir caused a build-up of carbon dioxide, hydrogen sulfide, and ammonia in the hypolimnion during stratified period in summer. Carbon Dioxide Carbon dioxide in natural waters is derived from a number of sources. It may enter surface water by absorption from the atmosphere, or may be produced in the water through respiration of organisms and as end products of organic matter decomposition. Lakes and reservoirs may receive additional CO from surface runoff and ground waters which 2 contain high carbon dioxide. However, the solubility of CO2 varies inversely with temperature of water and directly with atmospheric pressure. Over ordinary temperature range of water, carbon dioxide is much more soluble than oxygen. Reid (1961) reported that at 20° C and atmospheric pressure of 760 mm Hg, carbon dioxide dissolves about 0.88 volume compared with only 0.031 volume of oxygen at water equili- brium condition. Kerr, Paris, and Brockway (1970) stated that the quantity of CO exchanged at the airuwater interface depends on the 2 transfer rate, the concentration of CO2 in the air and water° They have given the amount of CO in saturation in water at equilibrium 2 46 with normal air ranges, from 0.4 to 1.0 mg COz/liter of water, depending upon the pH and buffering capacity. Natural water bodies are often supersaturated with CO however, as biological activity and chemical 2; reaction take place, they greatly reduce the concentration of carbon dioxide (Hutchinson, 1957). Kerr, Paris, and Brockway (1970) pointed out that the availability of any ionic species of carbon in an aquatic ecosystem is dependent upon: (1) direct additions and losses resulting from flow of the water mass; (2) the exchange between sediments and the water and between the water and the atmosphere; (3) chemical activity in the water; (4) removal from water by photosynthetic activity or excreted to water by aquatic animals; (5) photolysis of compounds and autolysis of organisms in the water; (6) secretion, excretion, and exchange phenomena within the biota; and (7) physical parameters of aquatic environment such as temperature, light, and pH. The presence of carbon dioxide in water enters into chemical combi- nation with water to form carbonic acid (H2C03) which in turn reacts with available limestones to form carbonates 04152 3 ) and bicarbonates (-HCO;), as the following reactions: CO +H_O *1 H CO 2 + - + — at at 2 2 2 3 H +HCO3 H +CO 3 The direction and end products of these reactions depend on the amount of free carbon dioxide and activity of organisms in natural waters. The changes in the amount of CO in the water that accompany respiration and 2 photosynthesis are related to acid-base relationships, particularly with relation to the hydrogen—ion concentration and the buffer capacity of water (Lee and Hoadley, 1967). 47 A major component of the buffering system of most natural waters -2 is largely affected by the CO -HCO3, -CO3 equilibrium system 2’ (Goldman, Porcella, Middlebrooks, and Toerien, 1972). They also stated that whenever the extraction of CO2 from water by algae through the photosynthetic actiVity occurs at a rate faster than it can be replaced it leads to an increase in pH value. Normally, the pH of natural waters at equilibrium with air is about 8.3 where bicarbonate is the major ion. Therefore, as CO is extracted from solution by growing 2 algae at a pH around 8.3, additional carbon dioxide is provided through the dissociation of bicarbonate alkalinity as expressed by the following equations: — —2 2(HCO3) 1 (CO3 ) + (H20) + (002) _ 1 _ (HCO3) + H20 H20 + CO2 + (OH ) As the pH rises, -CO3 becomes the major carbon species which can be converted directly to C0 by a hydration process as shown in the follow- 2 ing equation: -2 - 7. (CO3 ) + H20 CO2 + 2(OH ) These reactions indicate that when free CO2 content of water is insuf- ficient to meet the demand of the algae, the bicarbonate and carbonate forms can continually supply free CO2 for algal utilization. However, only a portion of the total inorganic carbon can be extracted during intense algae activity in a natural water principally buffered by CO -HCO3, -CO3 system. The reason is the metabolic 2’ inhibition of algal growth at pH between 10.0—11.0, thus placing an 2 upper limit on the amount of CO2 available from -HCO3 and CC; 48 (Goldman, Porcella, Middlebrooks, and Toerien, 1972). Although a water may contain a considerable amount of inorganic carbon as carbonate alkalinity, the amount of free carbon dioxide available at any point in time is fixed by the equilibrium reactions. These processes are more rapid than the physical uptake of carbon dioxide by the algae. There- fore, while utilization of carbon dioxide by the algae results in an equilibrium change, additional CO2 is supplied from the carbonate alkalinity system to meet the new equilibrium (King, 1970)° As previously discussed, the significance of 002 in natural waters has been recognized as a factor affecting the buffer system for decades, whereas little attention has been given to the importance of the CO2 regulation in eutrophication. Recently, more attention has been paid to the role of CO in the enrichment process in aquatic environments. 2 A number of investigators indicate CO as the most important limiting 2 nutrient in natural waters (Lange, 1967; Kuentzel, 1969; King, 1970; Morton, Derse, Sernau, 1971; Goldman, Porcella, Middlebrooks, and Toerien, 1972). A major cause of algal blooms in natural waters is the conversion of organic matter to CO through bacterial respiration. 2 Moderate increases in CO2 in water seem to speed up photosynthesis and the developmental processes of many organisms, but high concentra— tions may be definitely limiting to animals (Odum, 1959). The presence of decomposable organic matter and bacteria in lakes was found to produce massive algal blooms in spite of water containing not more than the minimum requirement of soluble phosphorus (King, 1970). He described it as the result of adequate amounts of CO available result- 2 ing from bacterial activity on decomposable organic matter stimulating a massive bluegreen algal growth. 49 Morton, Derse, and Sernau (1971) reported that the atmospheric replenishment of CO2 provides a sufficient supply for algal blooms, for at least 5.5 ft in depth, and can sustain growth rates of 1.5 to 2.0 mg/l/d. Waters and Ball (1957) found the increases in phytoplankton yield in bog lakes in northern Michigan occurred following an increase of -HC03 concentration in water as the result of lime addition to the lakes. Swingle (1947) reported that CO2 is a limiting factor in farm fish pond production. He found the fish yield was increased 43 lbs/acre per ton of stable manure fertilization, whereas an addition of 200 lbs of superphosphate to the manure increased production only 4.5 lbs above that for manure alone. Kerr, Paris, and Brockway (1970) found CO2 is an important factor in regulating the size of natural algal populations. They also found additions of carbon to a sterilized pond water are more important than additions of nitrogen and phosphorus in regulating the population size of axenic cultures of the blue—green alga, Anaoystis nidhlans. Acidity and Alkalinity Acidity and alkalinity of water refer to the amount of acids and bases present in the waters. Acidity in natural waters is usually caused by carbon dioxide, mineral acids, weakly dissociated acids, and the salts of strong acids and weak bases. While alkalinity is caused by strong bases and the salts of strong bases and weak acids which usually refer to the carbonate, bicarbonate, and hydroxide species. The total acidity of water is determined by titration with standard alkali up to pH 8.3 at the turning point of phenolphthalein indicator. Similarly, total alkalinity of water is evaluated by titration with standard acid to the turning point of methyl orange indicator at about 50 the pH 4.5 unit. The unit of measurement interprets in terms of milligram per liter or parts per million of solutes. Either acidity or alkalinity may be harmful not only in producing adverse acid or alkaline conditions, but also by increasing the toxicity of various components in waters. The addition of strong acids may cause the formation of carbonic acid in quantities that are adverse to the well being of the organisms. A reduction of about 1.5 pH units can cause a thousand-fold increase in the acute toxicity of a metallo- cyanide complex, whereas the addition of strong alkalis may cause the formation of undissociated NH OH or un-ionized NH 4 3 may be toxic. The availability of many nutrient substances varies with in quantities that the acidity and alkalinity (Moore, 1968). Hydrogen-Ion Concentration Hydrogen-ion concentration or hydrogen-ion activity or pH has been much studied in aquatic environments. The pH is considered as a limiting factor on aquatic organisms because it is not only a potential pollutant itself, it is also related intimately to the concentration of many toxic substances, particularly the weakly associated acids and bases. In natural waters, pH is closely associated with acidity and alkalinity in the buffer system. Carbon dioxide, bicarbonate, and hydroxide are parts of controlling the system. Changes in concentration of any member of the system cause a shift in the equilibrium resulting in a pH change. In freshwater, the pH varies widely compared with sea water. The fluctuations are always due to the composition of organic matter, inflow of ions from soils, runoff, and photosynthetic activity of aquatic plants. Warren (1971) reported that wide diurnal fluctuations of pH in natural waters can result from the photosynthetic activity of 51 algae and other submerged plants, rising during the daylight hours, and decreasing at night. Lee and Hoadley (1967) stated the variation of pH gradient in eutrophic lakes is caused by anaerobic metabolism of bacteria in the profundal zone. The magnitude of pH effects attributable to the biota is determined by the numbers, types, and activity of the organisms present as well as sunlight, turbidity, buffer capacity, and turbulence. Generally, pH ranges from 6 to 9 in ponds and lakes, and from 3.9 to 9.5 for streams (Ellis, 1967). In most productive freshwater lakes, the pH falls in the range between 6.5 to 8.5 (Moore, 1968). A change in the pH value of the surrounding water has been observed to have a marked influence on the life history of fish. However, the range of tolerance of fishes to pH varies, depending upon many factors such as stage of life cycle and the fish species, temperature, dissolved oxygen, acclimatization, and the content of various anions and cations (EIFAC, 1969). Naturally, the pH range which is not directly lethal to adult freshwater fishes is 5.0 to 9.0. More extreme pH values, perhaps even below 4.0 and well above 10.0, can also be tolerated for long periods by the most resistant species, and for short periods by more sensitive species (Doudoroff and Katz, 1950). Very young fish may be somewhat more sensitive to extremes of pH than adults. It has been reported that some freshwater fish embryos and larvae cannot live in waters which are only slightly alkaline (Brown, 1957). The pH has little influence upon the limits of temperature volun- tarily tolerated by brook trout (Creaser, 1931). The tolerance of fish to low concentrations of dissolved oxygen varies markedly with pH; for example, the bluegill sunfish showed suffering and some died in water of pH value 9.6 when the dissolved oxygen concentration was 5 ppm, but were unaffected by a pH value of 9.5 when dissolved oxygen concentration 52 was 10 ppm (Wiebe, 1931). Whenever the pH changes, the toxicity of several common pollutants is remarkably affected, such as the toxicity of sodium sulfide to trout tends to increase as pH changes from 9.0 to 6.0 (Jones, 1948). The toxicity of zinc to fathead minnows decreased with a fall in pH from 8.6 to 6.0, but it (tUi not continue to decrease as pH value was reduced further to 5.0 (Mount, 1966). The effect of pH on the food chain is considered as an important factor to interfere with the productivity of aquatic ecosystem. Streams with a pH range of 3.7 to 4.8 contained a large accumulation of undecayed plant debris (Harrison, 1956). In Belgium, Neess (1949) reported the productivity of ponds to be three times greater in the alkaline area (pH values 7.0—7.5) than in the acid area (pH values 5.0-5.6). He stated that low pH values affect the recirculation of nutrients in the aquatic environment by reducing rate of decomposition of organic matter and by inhibiting nitrogen fixation. Nitrogen Nitrogen is one of the fertilizing elements essential to the growth of algae in waters. Stumm and Stumm-Zollinger (1972) reported that it is more important in the estuary and marine waters than in freshwater. Mackenthun (1969) indicated that a concentration of 0.30 mg/l (PPm) inorganic nitrogen is critical for stimulating algal growth if the water contains adequate phosphorus. In general, nitrogen is present in water either as dissolved organic nitrogen or as inorganic nitrogen such as ammonia, nitrite, nitrate, or as elemental nitrogen. Organic nitrogen enters the water by a distribution of dead organisms and their constitu- ents, such as amino acids, polypeptides, protein, and animal metabolic wastes as urea and uric acids. Ammonia nitrogen is considered as an 53 indication of an anaerobic decomposition or sanitary pollution. A presence of free ammonia in concentrations over 2.5 ppm in neutral or alkaline waters is harmful to many species of freshwater organisms (Reid, 1961). Nitrite nitrogen is an intermediate stage in the nitrogen cycle and is generally present in only trace amount (0.10 ppm); however, it may be higher in sewage effluents. Nitrite is converted to nitrate fairly rapidly. Nitrate nitrogen usually occurs in relatively small concentrations in unpolluted freshwaters. In natural waters, ammonia and nitrate are the important sources of nitrogen for growth of phytoplankton and bacteria. The capability in using organic substrates varies widely in different species of phytoplankton and type of organic nitrogen compounds. Many amino acids are found to support growth as well as nitrate (Goering, 1972). He also pointed out that ammonia is derived from the transforming organic nitrogen to inorganic nitrogen in the sediments which diffuse into the overyling water. Its concentration had significantly increased from surface to deeper layers of the sediments to a depth of 1.65 meter. In oxidizing sediments, ammonia is transformed to nitrate by nitrifying bacteria. Nitrate is a soluble nutrient and is capable of diffusion from the sediments to the overlying water. It also undergoes reduction to molecular nitrogen (denitrification by bacteria) in the anaerobic condition. Chen and others (1972) reported that the rate of nitrate nitrogen losses under aerobic condition was less than half of that in the anaerobic system. The role of nitrogen in the reservoirs is complicated. One possible explanation is given by Brezonik, Delfino, and Lee (1969). They reported their observation on the water chemistry of the nitrogen in Cox Hollow Lake, a man-made lake in southwestern Wisconsin. They found that while 54 the lake was still stratified and the hypolimnion was in an anaerobic condition, nitrate was undetectable throughout the water column, nitrite was extremely low, and ammonia was virtually depleted in the epilimnion, but was higher in the hypolimnion. The nitrification process occurred immediately after destratification. Nitrate was found in trace amount as soon as the hypolimnion became oxygenated, and reached its highest level at the end of summer. Furthermore, Prochazkova (1966) found the fluctuations of nitrate in a reservoir are associated with the variations of the water level and density of the inflows. He reported that an increased water flow in the Slappy Reservoir in Poland during the warm season was accompanied by an increased nitrate concen- tration at the surface as a result of the mixing process of a denser water inflow and impounded water. Neel (1967) stated that the presence of nitrate nitrogen in reser- voirs usually appeared with large numbers of 200plankton and at a low level of ammonia nitrogen. Nitrate exhibited a small variation in the average annual concentration, but it might disappear for months at a time. In Fort Randall Reservoir, it was less concentrated in deeper layers than near the surface in 1954, but during other years its maxima varied between surface and bottom, usually being high near the surface when low near the bottom or vice versa. Its concentration decreased with phytoplankton blooms. Furthermore, he reported that a decline of phytoplankton was usually associated with an increase in ammonia nitrogen, and a build-up of plankton pOpulations induced a decline in ammonium compounds. He found the average annual ammonia nitrogen concen- tration in Fort Randall Reservoir declined from 0.60 ppm in 1952 to 0.09 ppm in 1954, and then built up again to 0.25 ppm in 1957. It increased from 0.00 ppm in 1954 to 0.25 ppm in 1956 in Garrison fibrEfiaH¥ rcnguflilun,zlj . _ .- - V 55 Reservoir, and it grew from 0.10 ppm in 1955 to 0.20 ppm in 1956 in the Gavins Point Reservoir. Phosphorus Phosphorus is an important element for the growth of aquatic vege- tation. Only small amounts of phosphorus (0.01 mg/l) are capable of encouraging the growth of phytOplankton, algae, and other aquatic plants. The presence of phosphorus in natural waters is dependent upon the quantity of phosphorus in rocks and soils, water runoff, domestic and industrial wastes, household detergent, the fertilization of agricul— tural lands, and the annual cycles of mixing of the water body (Reid, 1961; Keup, 1968). However, the concentration of phosphorus in a surface water body cannot be predicted merely on the basis of the supply and of the hydro- graphic conditions, because a major proportion of nutrients must be regenerated from organic debris. Juday and his colleagues (1927) found the soluble phosphorus was uniformly distributed from surface to bottom of the lakes during the spring circulation. 0n the contrary, there was an increase in concentration of soluble phosphorus in the lower strata during the summer stratification period. They stated that a high concentration was the result of soluble phosphorus release from decompos- ing organic matter of the sediments. The amount was two to ten times greater than that presented in the surface water. Hutchinson (1957) indicated that the total phosphate in natural waters depends largely on the geochemical condition, usually being greater in water derived from sedimentary rock in lowland regions than in a water draining the crystal- line rocks of the mountain ranges. He stated that the soluble phosphate usually is of the order of 10 percent of the total phosphorus. There 56 may be a great decrease in total phosphorus in the surface water at times of algal blooms in summer, when the soluble phosphate is undetectable. The distribution of phosphate between the sediments and overlying water is of considerable importance for the productivity. It was found that different types of sediments varied in their ability to support algal growth by the amount of phosphorus available in these sediments (Porcella, Kumagai, and Middlebrooks, 1970). They stated that the phosphorus in the sediments is present in several forms such as a mineral, adsorbed to surfaces of other minerals, in a solution in the interstitial water, and as organic phosphorus. The availability of a soluble orthOphosphate in the overlying water in a sterile environment is dependent upon complex chemical, biological and physical reactions. In the reservoirs bacteria play an important role in the process of removing phosphorus from organic matter and actually keep the phosphorus available for uptake by phytOplankton, periphyton, and attached aquatic plants. Furthermore, it is very interesting that not only phosphorus in the water stimulates the primary production in reservoirs, but Chalupa (1960) reported that the atmospheric phosphorus (P205) is important in stimulating primary production of phytoplankton in the epilimnion of the Sedlice Reservoir, Czechoslovakia, during thermal stratification periods when the penetration of inorganic phosphorus from the bottom layers cannot supply the demand for phytoplankton growth in the surface layers. Neel (1967) reported that the concentration of total phosphorus generally showed an increase with age of reservoirs. He found the average annual concentration increased from 0.18 ppm to 0.79 ppm over the period 1955-57 in the Garrison Reservoir. It increased from 0.04 to 0.24 ppm over the period 1952-55 in Fort Randall, and declined to 0.17 in 1956, and then grew up to 0.26 ppm in 1957. In Gavins Point Reservoir, it 57 increased from 0.19 in 1956 to 0.29 ppm in 1957. He indicated that the concentration of phosphorus decreased during the plankton blooms and increased as the plankton declined in all of these reservoirs. McCarraher and others (1971) reported that the concentration of phosphorus in the McConaughy Reservoir in Nebraska varies with season. It increased in late spring and summer, from May to August, and declined in the fall, from September to October. However, its concentration was generally higher than 0.10 ppm. Sulfur Sulfur is widely distributed in freshwater as the sulfate-ion which is chemically stable in aerated water and forms salts of low solubility such as calcium sulfate, sodium sulfate, and others. The concentration of sulfates in freshwater usually lies between 3-30 ppm (Hutchinson, 1957). He also noted that under aerated waters the sulfate concentra- tions in lakes increase with depth but decrease in the hypolimnion water of stratified lakes. In the Soviet Union, Ivanov (1964) remarked that the concentration of sulfate in freshwater reservoirs was usually low; thus, it may be considered as a limiting factor. To support his assump- tion, he made a comparative analysis of several eutrophic lakes (Below, Bol'Shoe Kucheer, Chernoe Kucheer, and Solenoe). He found the production of organic matter in the lake waters increased in proportion to that of the sulfate. Hutchinson (1957) pointed out that under anaerobic conditions, sulfate can be used as a hydrogen acceptor in the metabolic oxidation of organic matter by certain bacteria. The reduction of sulfate to hydrogen sulfide occurs chiefly in the mud deposit and in part in the water itself. Ivanov (1957) reported that the formation of hydrogen sulfide in the 58 surface of sediments in Lake Sernoe was 1.0-1.4 mgHZS/l(mud)/24 hrs, compared with very small limits of 0.02-0.05 mgH23/1/24 hrs in the lake water. Zhadin and Gerd (1961) stated that the concentration of hydrogen sulfide is also highest above newly flooded soils of the reservoirs. The concentration of 10.0 mg/liter was found in the bottom layers of a stratified eutrophic reservoir for several weeks during mid-summer (Ridley and Symons, 1972). They also found that a continuous destrati- fication will inhibit the sulfide formation and reduce its concentration to the tolerable levels. The oxidation of hydrogen sulfide occurs either at the mud surface or in the water column and is mediated by pigmented and non-pigmented sulfur bacteria and various thiobacteria (Ivanov, 1957). His experi- ments showed that the pigmented sulfur bacteria oxidized hydrogen sulfide to sulfate only in the presence of light, while the thiobacteria oxidized it to an elemental sulfur either in darkened or lighted vessels. Hydrogen sulfide is a very severe toxicant to aquatic life, especially to fish. Lethal concentrations of hydrogen sulfide which would limit the survival of eggs and fry, and food supply for fish, have been studied for years. Recently, Smith and Oseid (1972) experimented with the effect of hydrogen sulfide on eggs and fry of freshwater fishes at a concentration between 0.013 to 0.087 ppm and between 0.005 to 0.086 ppm respectively. They reported that at these ranges of concentration, it can result in either prolonging incubation period, deformed fry, slow growth, or death in many species such as walleye, sucker, trout, and northern pike. They also remarked that its toxicity was higher at lower' levels of dissolved oxygen concentration. 59 I593 Iron is an essential element for both plant and animal metabolism (Oborn, 1962); therefore, all activities in the biosphere may have a strong influence on the occurrence of iron in water. Gerloff and Skoog (1957a) stated that the critical level of iron for the blooms of.Micr0— cystis aeruginosa in southern Wisconsin lakes was approximately 100 ppm. Oborn and Hem (1962) believed that the iron content of impounded water is influenced by aquatic vegetation, both rooted and free-floating forms. Hem (1970) stated that bacteria may also effect either an increase or a decrease in dissolved-iron concentration in water. Generally, the occurrence of iron in surface waters and even groundwater is strongly influenced by sediments, domestic sewage, industrial wastes, acid-mine drainage, and inflows of thermal springs which carry high concentration of ferrous and ferric ions. The occurrence of iron in lakes and reservoirs is usually associated with the stratification. Stumm and Morgan (1970) stated that when the hypolimnetic waters are devoid of dissolved oxygen, conditions are favorable for the reduction of ferric oxide in the water overlying the sediments to the ferrous ion at the mud-water interface. The soluble iron contents of the water overlying the sediments will progressively increase during the stagnation periods. When fall and spring circula- tions occur, dissolved oxygen is distributed to the hypolimnion, and most of the soluble and suspended bivalent iron is reoxidized to insoluble oxide and deposited in the sediments. The continuous sequence of circulation and stagnation is accompanied by the oxidation and reduc- tion as well as the precipitation of iron in lake sediments. A report of the Lake Tahoe Area Council (1971) indicated that iron in the influent water of Indian Creek Reservoir is utilized in biological 60 activities in the impoundment. They pointed out that a decrease of iron content in impounded water during summer was a result of taking up of influent iron by aquatic organisms, while iron remained unchanged due to lack of biological activity during winter. Furthermore, Roeder and Roeder (1966) carried out experiments on the effect of iron on the growth rate of the swordtail, Xiphophorus heZZeri, and the platyfish, Xiphophorus maculatus, by using daily addition of ferrous sulfate. They found the growth rate increased and also mortality significantly decreased from hatching to maturity. Manganese The role of manganese in water is closely related to that of iron. It is an essential element to both plant and animal life (Myers, 1961). By nature it is widely distributed in rocks and soils as oxides, hydroxides, and carbonates. In freshwater, it is frequently present in underground springs and in the bottoms of lakes and reservoirs as soluble or insoluble substances, and as organic matter. Ingols and Wilroy (1962-63) stated that the concentration of manganese in fresh- water depends on the geology and quality of water. They found a high value of dissolved manganese in a water supply reservoir in the Piedmont plateau region of the southern United States. A high concentration develops quickly in the impoundments where the temperature in the bottom pool ranges from 23° to 28° C. However, the concentration in ground- water and surface waters is often small because of a limited solubility of MnCO3 and MnS which seldom exceeds 20 mg of soluble manganese per liter (Stumm and Morgan, 1970). Manganese entering the reservoirs will undergo a cyclic transforma- tion. Oxidation precipitates manganese from top waters. Poon and 61 DeLuise (1967) stated that the biological reduction and transformation, organometallic complexion, together with the presence of CO and the 2 lowering of pH all have some effect on the solubility of manganese. The enrichment of soluble manganese in the hypolimnion of lakes and reservoirs during the stratification period may occur by the following processes: (a) a decrease in pH by heterotrophic activity will shift the exchange-adsorption equilibrium in such a way as to desorb Mn++ from the higher valent manganese oxides and from ferric oxide; (b) a reduc- tion of ferric oxide releases sorbed Mn++; (c) the ferrous ion and other reductants (8‘2, organic material) can reduce manganese oxides and render them soluble (Stumm and Morgan, 1970). They also pointed out that when the hypolimnion becomes aerobic during the fall and spring overturn, most of the soluble and suspended bivalent manganese is reoxidized to insoluble oxides and settle to the bottom. Brezonic, Delfino, and Lee (1969) reported that the destratification of Cox Hollow Lake in southern Wisconsin caused a marked decrease in hypo- limnetic manganese concentrations, from 2.0 mg/l to about 0.2 mg/l within 10 weeks. Nutrient Removal High levels of nutrients present in lakes and reservoirs cause a potential hazard with respect to the degradation of the impoundments through the excessive growth of nuisance aquatic vegetations. There- fore, nutritional limitation has been required as a means of controlling the enrichment of the water bodies. Most attention has been directed towards the fluctuations of nitrogen and phosphorus. Many procedures have been practiced for the removal of both nutrients from.waste water and polluted streams. These methods include the ion-exchange, 62 electrochemical treatment, chemical-biological process, and harvesting of hydrophytes (Bell, Libby, Lordi, 1970; Sadek, 1970; Mechalas, Allen, and Matyskeila, 1970; Gianelli, 1971; and Reeves, 1972). Among these methods, algal harvesting seems to be the most feasible procedure to remove nutrients from impounded waters as also does other hydrOphyte removals. In fact, if the algae are removed from the water before they die, it will stop the recycling of nutrients back into the water by decomposition. Then, troublesome fertilizing elements will be decreased for subsequent generations of algae; therefore, their growth is restricted. A few studies have dealt with nutrient removal from water by harvest- ing algae and other aquatic plants. Mechalas, Allen and Matyskiela (1970) reported that nitrogen can be removed from wastewater either as the proteinaceous cell material by living cell assimilation of ammonia, or as the free N2 or N20 gas by denitrification. Gianelli (1971) studied the effectiveness of nitrate removal from tile drainage by an algal system; he reported that approximately 95 percent of algal cells (Scenedesmus quadricauda) in water can be harvested by flocculation and sedimentation, followed by filtration of the sediments. He found this method capable of removing from 70 to 85 percent of the nutrient nitrogen. The concentration of nutrients in some shallow, weed-infested eutrophic lakes can be reduced by removal of natural vegetation or cultivated hydrophytes (Boyd, 1970). He also recommended ideal species for cultivating in the impoundments; it must produce large standing crops per unit area, have a rapid growth rate, and accumulate large quantities of mineral nutrients, particularly nitrogen and phosphorus, plus having a reasonable nutritive value as a feedstuff. He cited that 63 the water hyacinth (Eichornia crassipes), alligator weed (Alternanthera philoxeroidbs), water willow (Justicia americana), and cattail-(Yypha Zatifblia) are most suitable for these purposes. These species are both emergent and floating plants which are handy to harvest by harvesting equipment or by hand at a fairly continual rate or annually. Fitzgerald (1971) suggested that the ability of sorption of phosphorus by lake muds under aerobic condition may be used to remove phosphorus from the lake water. He found as little as 0.4 gm of lake mud can sorb about 0.05 mg POA—P in less than 30 minutes. His prelimi- nary tests with SéZenastrum sp. and CZadophora 8p. indicated that lake muds under aerobic condition did not provide available phosphorus and nitrogen to algal species when exposed for a period of one or two weeks, while less than 1 percent of the total phosphorus in lake muds taken from the hypolimnion (18 m deep) in Lake Mendota was found to be available for algal growth under equivalent conditions. Furthermore, Engelbrecht, O'Connor and Ghosh (1965) reported that the treatment methods for the removal of iron from water supplies can be done through the aeration to provide enough oxygen for the oxidation of soluble ferrous forms to the insoluble ferric forms. The same phenomenon also applies in the case of the manganese problem in the water (Ingols and Wilroy, 1962). AQUATIC PRODUCTIVITY Aquatic productivity is essentially the fixation of inorganic carbon into new organic material by means of the biogenic minerals and solar energy. Thus, it is the activity of producer organisms (chiefly green plants). In water, the process is controlled by the interaction of several factors which are usually divided into three groups: firstly, 64 the physical factors originating from solar radiation such as light intensity, temperature, mixing and turbulence caused by wind action; secondly, the content of nutrients in the water body; thirdly, the interaction of organisms present in an aquatic community which may promote or hamper the production of certain species (Findenegg, 1965; Russell-Hunter, 1970). PhytOplankton The production of phytoplankton in reservoirs is one of the most interesting studies to aquatic biologists. Attention has centered on the effects of environmental changes that influence the growth of phyto- plankton in established impoundments. The major environmental factors include types of reservoirs, site of reservoirs, climatic condition, surface area, water depth, light penetration, water temperature, and fluctuations of nutrient contents in the water bodies. Taylor (1971) has studied the response of phytoplankton productivity in six TVA reservoirs to nutrient availability correlated with certain environ- mental ccnditions. He found a short retention time affects the main- streamreservoirproductivity by limiting time for the phytoplankton growth. While a long retention time of storage impoundments and multi— purpose reservoirs provides more time for phytOplankton growth as a result of longer period of availability of dissolved nutrients and the higher temperature of the impounded water. Latitude and nature of the soils over which the reservoir lies or which is drained by inlets influence water temperature and its enrichment. In the temperate zone, a pattern of seasonal fluctuations of the dominant species blooms is greatly altered by local climatic conditions, especially by tempera- ture and precipitation (Funk and Gaufin, 1971). A similar result is 65 reported in the tropics (Sreenivasan, 1970). He found the climatic features tend to support high productivity of reservoirs as a result of greater light intensity, longer hours of sunshine, and warmer temperature. Reservoirs with greater surface area usually have higher produc- tivity than the smaller ones because more energy is absorbed from the solar radiation. Sakamoto (1966) remarked that the primary production of phytOplankton in some Japanese lakes is dependent on lake depth. The growth of algae is influenced directly by intensity of light and duration of illumination which govern the energy supply for photo— synthesis (McCombie, 1953). In Czechoslovakia, Stepanek (1965) reported that the average number of phytoplankton of the vertical water column of the Sedlice Reservoir depends on the duration of sunshine. His statement was supported by Sreenivasan (1970), who found an increase in light penetration in the major reservoirs in Madras State, India, leading to an increase in the primary production of the impoundments. The seasonal fluctuations in primary production of the Ivankovo, Rynbinsk, and Kuibyshev reservoirs in the Soviet Union were dependent on the variations in sunlight intensity, and the maximum production of photosynthesis of these reservoirs occurred with increased solar radia— tion in July (Pyrina, 1966). The influence of temperature on primary production is well known, a higher temperature coincides with increasing photosynthetic activity. In the temperate zone, an increase of phytOplankton during the spring will be accompanied by a rise in water temperature which tends to accelerate the growth rate. On the contrary, the decrease in the fall will be accompanied by a decrease in temperature which will slow down the growth rate. In deep reservoirs, the development of thermal 66 stratification during summer prevents a circulation of nutrients within the water body causing a shortage of nutrients then a decline of phyto- plankton productivity. The investigation of nutrients controlling the production of phyto— plankton in freshwater is usually referenced to nitrogen and phosphorus. Recently, more attention has been given to the role of carbon as a limiting factor to primary production. Prescott (1962) remarked that a luxuriant growth of phytoplankton can only be found in a water body which is abundantly supplied with C02. His statement is supported by Schindler and Nighswander (1970), who found a significant increase in phytoplankton production in Canadian Shield lakes with an increased carbon dioxide. Schindler (1971) investigated the interactions of carbon, nitrogen, and phosphorus with reference to their effects on phytoplankton productivity by the bottle bioassay experiments. He found the greatest increase in primary production resulted from addi- tion of carbon, while some response was detected in the phosphorus- enriched set, but no additional production resulted from nitrate addition. However, nitrogen and phosphorus are still considered as the major nutrients for stimulating the growth of phytoplankton in freshwater bodies. There are a number of reports which confirm the importance of nitrogen and phosphorus as the limiting factors for the growth of phytoplankton. For example, Prescott (1962) indicated that there was a negative correlation between concentrations of these nutrients and water blooms. He pointed out that high phytoplankton population caused a decrease in nitrate and phosphorus content in the water, because these nutrients were being consumed and stored in the organisms. When the phytoplankton decreases through an accelerated death rate and 67 disintegration occurs, the elements are released and their percentages in the water rise. This phenomenon is also reported by Schindler and Comita (1972). Sakamoto (1966) found a close relation existed between the chlorophyll content and the total nitrogen and total phosphorus content in the epilimnion layer of various Japanese lakes and ponds. In the tropics, Khan and Siddique (1971) found phosphate phosphorus was directly related to gross primary production in a fish pond at Aligarh, India. Funk and Gaufin (1971) investigated the productivity of phyto- plankton in a Wyoming Cooling-Water reservoir. They found a high correlation between increased quantities of nitrates and organic phosphates and the blooms of Pandorina morum and Aphanizomenon ons-aquae. In general, the seasonal distribution of phytoplankton is bimodal, with minimal numbers in winter and mid-summer and the maxima in spring and fall in the temperate region (McCombie, 1953). In the tropical region, the maximum is during post winter months (March to May) and minima are during winter (February) and monsoon months (July and August) (Khan and Siddique, 1971). The populations of phytoplankton of many lakes in the temperate zone are remarkably similar with respect to the proportions in which different algal groups are represented in the annual crOps. McCombie (1953) reported that when the spring and fall maxima develOp, the population is comprised chiefly of diatoms (Bacillariophyceae), and these make up the greater part of the total annual net phytoplankton crop. During these periods the Crysophyceae (e.g., Synura, Chrysosphaerella, and Dinobryon) may also be present in considerable numbers. Next in importance (numerically) to the diatoms in the annual crop are the blue-green algae (Myxophyceae) which appear during summer and reach the peak abundance towards mid-summer when diatoms are at a minimum. Green algae (Chlorophyceae) are also present 68 during summer, but generally form a small part of the total annual crop° His statements were confirmed by Hartman and Graffins (1960), who investigated the quantitative seasonal changes of phytoplankton communi- ties in the Pymatuning Reservoir in northwestern Pennsylvania. They found the occurrence of summer communities dominated by blue-green species, spring and fall communities dominated by green species, and winter communities with greens and diatoms as co-dominants. In the Soviet Union, Kalashnikova and Sorokin (1966) reported that the production of phytoplankton in the Bratsk Reservoir was highest in May, then decreased by half in June and remained at this level until the end of summer, and sharply dropped in September. They stated the decreased production in mid-summer is undoubtedly caused by a deficiency in the biogenous compounds. Nutrients are used up in spring during the development of diatoms and evidently they are not regenerated in an adequate amount in summer as a result of thermal stratification. In the tropics, the seasonal variations in quantity and species composition of phytoplankton show non-uniform patterns from year to year. Govind (1963) reported his preliminary studies on plankton of the Tungabhadra Reservoir in India during 1959 to 1961. He found two peaks in January and August of 1959, and in April and June of 1960, but three peaks in 1961, in January, June, and October. Whereas the species compositions of the peaks in August 1959 and June 1960 were dominated by green algae, in June 1961 it was blue-green algae, and in August of both 1960 and 1961 with diatoms. Sreenivasan, Raj, and Anthony (1964) published similar results on the studies of plankton in Bhavanisagar Reservoir in Madras. They found two peaks during 1961, one in January and another in December. But in 1962, the peaks were in March and June. Dominant species fluctuated from time to time, with 69 Microcystis in large numbers in January-February, then in August in 1962. Diatoms were abundant in December 1961, but dominated in 1962 for the major part of the year except in October and November. Lakshminarayana (1965) in his studies on the seasonal growth and succession of phytOplankton in the River Ganges, Varanasi, India, con- cluded that the greatest crops of phytoplankton occurred in winter and summer, the lowest numbers during the rainy season. However, from the middle of March to the end of June, the blue-green algae became dominant over diatoms and green algae. During the rainy season (July to October) the river reached high flood levels which resulted in dilution of phytOplankton. In the winter months (November to February) the phyto— plankton especially diatoms was gradually increased with the decreased water levels and the onset of winter. Benson and Cowell (1967) reported that the benthic algae or peri- phyton were widely distributed in shallow sections of the Missouri River reservoirs. They found submerged trees are the important sub- strates for periphyton growth in the impoundments. The periphyton standing crop reached a maximum in May and a minimum in June. Prowse (1953) found the abundance of periphyton on the bottom is more associ— ated with light intensity than a high nutrient content at the muddwater interface or of the sediments. Claflin (1968) stated that seasonal distribution of the periphyton standing crop in Lewis and Clark Lake was maximal in May, then rapidly declined in June and July. In August, the standing crop increased slightly. Before and during ice cover population densities were low, then increased in spring. In Lake Francis Case, the population increased rapidly to a maximum level in mid-July, declined in August, and subsequently dropped to minimum level in late September when the water level was lowered and exposed substrates. 70 Aquatic Macrophytes Aquatic vegetation growth is closely bound up with the.general management regime of the water body. Higher aquatic plants play a prominent role in reservoirs. They decrease reservoir size, make them more shallow, and eventually return them to dry land. A wide distribu- tion of macrophytes affects the physical and chemical qualities of the water--its transparency, coloration, and smell. It may serve as a barrier to the entrance of suspended matter affecting the deve10pment of phytOplankton (Kabanov, 1961). The macrophytes include emergent, floating, and submerged species. Most emergent species occur in shallow water less than six feet deep (Penfound, 1956); submerged plants occur in all photosynthetic depths and floating species occur over all the surface unrelated to depth. Aquatic macrophytes invade shallow water areas and entrap particu- late silt which is carried into the impoundments. These types of aquatic plants continue Spreading farther from the shore as water areas become more shallow and the bottom mud provides more nutrients. Further- more, several physical factors in reservoirs are developed to favor their growth, including light penetration, turbidity, water temperature, wave action, flow velocity, water depth, water level fluctuations, and type of bottom sediments (Mackenthun and Ingram, 1967; Peltier and Welch, 1970; Boyd and Goodyear, 1971). The emergent plants are usually more productive than submerged and floating plants (Boyd, 1971). The species composition and character of aquatic plants are reliable indexes of features of the hydrobiological regime of the water body. Pashkov, Kruglova, and Malovitskaya (1957) found the change in species composition of the aquatic vegetation in the Veselyi Reservoir, USSR, coincided with a considerable increase in depth, decrease in 71 salinity, and type of deposits. Peltier and Welch (1970) found that deposition of enriched sediment is a prime cause of aquatic plant growth in the Pickwick Reservoir on one hand, but sediment may smother seeds and reduce growth of plants that already have germinated. However, the seasonal changes in biomass usually increase rapidly in the spring and reach a maximum in summer (Westlake, 1965). Aquatic macrophytes affect many aspects of morphology and biology of the reservoirs. Their presence in dense mats may impede or completely prevent navigation and recreational uses, promote loss of water either by water replacement or transpiration. Large amounts of aquatic plants may create deoxygenated conditions where fish cannot live and make fishing Operations difficult or impossible. On the other hand, they may provide suitable habitats for spawning and feeding of the young as well as for invertebrates that serve as food for the fish. Penfound (1956) reported that aquatic macrophytes are of considerable value to small aquatic animals since they provide them better shelter, food and oxygen. He pointed out that the productivity of animals in an aquatic environment varied with type of aquatic plant and its influence. In general, emergent plants favor high productivity of migratory water- fowl and aquatic mammals. Submerged species are especially useful in the production of animals which spend all or most of their lives in the water. Floating plants vary greatly in their capacities to support aquatic animals. He found AzoZZa carolineana, Lemna minor, and Spiro- dela polyrhiza are known to reduce the oxygen content of the water bodies far below the minimal requirements of fish, whereas floating leaf plants such as Brasenia purpuream, Nelumbo Zutea, and Nymphaea adorata also reduce oxygen tension of bodies of waters even though not so drastically as the previous species. Smirnov (1963) has studied the 72 distribution of the inshore Cladocera of the Rybinsk Reservoir on the Volga. He found the aquatic vegetation areas near shore affect the abundance of fauna several times exceeding the density of the fauna in non-vegetation areas. Straskraba (1965) stated that the littoral zooplankton in the Labicko Lake were found more abundantly near the lake surface over the areas of dense submerged vegetation, the concenr tration observed being five—fold for Crustacea and two-fold for Rotatoria. Petr (1968) reported that the Cerataphyllum demersum and Pistia stratiotes are the most abundant aquatic plants of the Volta Lake in Ghana, and form an important habitat for many aquatic inverte- brates especially during February to November. The invertebrates serve as a major source of food for fish in the impoundment. Nevertheless, their habitats on both plants are greatly influenced by the physical and chemical properties of water during the season of Harmattan Winds in February and March and during the flooding season. The abundance of total biomass of animals on inshore weeds was about 15 times higher than that of offshore plants in April. The two main groups of animals inhabiting Pistia root were Dipteran larvae and Odonata nymphs. A decrease in number and weight of both groups occurred from February to April, whereas Crustacea and Mollusca were the next most abundant groups which increased in March and then were found lowest in April. The total standing crop increased from May with more or less fluctuat- ing abundance and finally was interrupted by a complete disappearance of Pistia in December. McLachlan (1969) reported that rooted littoral aquatic plants affect the productivity of benthos. He found the presence of Potamogeton pusiZZus, Ludwigia stoloniféra, and Ceratqphyllum demersum in newly created tropical reservoir, Lake Kariba, in Rhodesia-Zambia, resulted in 73 an increase in the biomass of benthos with the appearance of several new species. The rise in faunal biomass per unit area of the lake followed the invasion of aquatic plants and was a result of the presence of bentic fauna on the plants. However, mats of floating plants such as Salvinia auriculata tended to cause a decrease of benthos on the bottom below it as a result of deoxygenated condition. ZooPIankton The formation of a zooplankton community in reservoirs is of interest to fishery biologists since it plays an important role for the development of the ichthyofauna. They are the main source of food for small fish in the post-embryonic active feeding period, and for plankton-eating fish. The development of zooplankton in reservoirs varies with environmental factors such as location, the physicochemical characteristics of impounded water, and season. In general, the standing crop of zooplankton in a reservoir increases downstream as a result of reducing current and turbidity (Cowell, 1967). A high quantity of zooplankton in the Dubossary Reservoir on the Dniester River was a result of decreasing current velocity and turbidity, associated with physico-chemical changes following the construction of the dam (Grimal'skii, 1957). At the same period, Dzyuban (1957) reported that the process of zooplankton community formation in the reservoirs on the Volga and the Don took approximately 2—4 years, and may take longer if the filling period is prolonged over several years. It has been noted that a sharp increase in the biomass of zooplankton occurs after damming is a result of a rapid development of bacteria and phytoplankton to provide more food for their growth and reproduc- tion (Prirozhnikov, 1961). He stated that the largest biomass of 74 zooplankton in most reservoirs occurs in the middle and lower sections as shown in Table 1 (Pirozhnikov, 1972). As soon as the zooplankton community has formed in the reservoirs, some fluctuations in its composition and numbers are observed every year. These changes result from the variations of environmental condi— tions such as a low or high water year, change in water level and flowage in the reservoirs, meteorological condition changes, a sporadic increase Table 1. Quantitative indices for summer zooplankton in the major zones of a reservoir and upper river in the Soviet Union (From P. L. Pirozhnikov, 1972) Total biomass,gm/m3 Reservoir zones Reservoir River Upper Middle Lower Kaunass 0.4 — 2.5 3.7 Kremenchug 0.97 6.0 6.56 10.0 Tsimliansk 1.05 1.6 1.86 0.8 Gorky - 1.1 2.8 2.6 Volgograd 0.88 1.4 4.7 1.7 Novosibirsk 0.02 0.4 1.5 2.2 Bratsk 0.1 0.2 0.9 0.8 in development of some species, and also the nature or source of water supply to the reservoirs (Dzyuban, 1957). He found the abundance of zooplankton was lower in years of high water, compared with the years of low water. He described that in high water years, the concentration of nutrients in reservoirs was diluted by more impounded water. Depth was increased; thus, there was a large degree of stratification developed to inhibit the regeneration of nutrients from the sediments. Further- more, it impeded the vertical distribution of zooplankton to the bottom and decreased their survival rates by making them more conspicuous to 75 sight-feeding animals. Zhadin and Gerd (1961) reported that reservoirs supplied by water from rivers are characterized by the growth of zoo- plankton biomass towards the dams. A similar growth is observed in reservoirs that are supplied by water from an upstream reservoir. This type of reservoir is also influenced by the discharge of zooplankton from an upstream impoundment. Cowell (1967) reported that a discharge of zooplankton from Lake Francis Case, 80 km upstream, has considerably more influenced the standing crop in Lewis and Clark Lake than the effect of the water exchange rate, or the inflows from tributary creeks. The 200plankton in reservoirs differ considerably in species composition, the dominant species, and total number of species. Roll and Tseeb et a1. (1957) reported that the main biomass of zooplankton in the Kakhovka Reservoir in the USSR began to develop three months after the beginning of the rise of the water level. The biomass pre- dominated with cladocerans and c0pepods in approximately constant pro- portion, whereas rotifers were insignificant. When the reservoir attained its projected size, the differences in zooplankton in differ- ent parts of the reservoir appeared. They found a small biomass of rotifers in the upper reach which was the area of most powerful current (0.5-2.0 m/sec) and high turbidity. The middle stretCh of the reservoir was dominated by cladocerans and c0pepods which composed 35-60 percent of the total zooplankton in this region. In the lower reach, clado- cerans especially Daphnia decisively dominated by the end of May (up to 70 percent of the total biomass). The relative distribution of zooplankton in the reservoirs of the United States has been reported by many investigators. Cowell (1967) reported that the zooplankton of Lewis and Clark Lake was dominated by cyclopoid c0pepods in the headwaters and near the dam. Calanoid 76 c0pepods were most abundant in the upper end of the reservoir, and cladocerans were at stations near the dam. Applegate and Mullen (1967a) found c0pepods and cladocerans (except Daphnia) occurred in greater numbers in the midrregion of the Bull Shoals Reservoir rather than in the lower part near the dam. The number of rotifers per unit area were also highest in this region. Kochsiek, Wilhm, and Morrison (1971) found rotifers were most common in the upper reaches in Keystone Reservoir, and also were most frequent. Cladocerans and c0pepods were reported in abundance in the lower region where turbu- lence was less. The mean annual zooplankton density was higher in the middle section than in the upper and lower sections of either the Cimarron arm or the Arkansas arm of the reservoir- They gave the reasons for low density of zooplankton in the upper portion as the effect of low food supply, strong turbulence, and wide ranges of the physico-chemical variations of impounded waters. Moreover, for. the lower portion they pointed out that it may probably be influenced by the position of penstock—intake and the regulations of the discharges. In the tropical zone, the density of zooplankton has been correlated closely with the weather conditions. Govind (1968) reported that the southwest monsoon (May to July) rainfall seemed to influence plankton production in the Tungabhadra Reservoir in India more than the north- west monsoon (October to December). He found typical zooplankton in this reservoir comprised mainly of Rotifera, Cladocera, and Copepoda; however, c0pepods generally dominated over all other groups. The density of zooplankton in reservoirs varies basically with localities and seasons of the year. Roll and others (1957) have studied the fluctuation of zooplankton in the Kakhovka Reservoir, USSR, during its first year of existence. They reported that cladocerans were 77 insignificant over the entire area of the reservoir in spring.except for the bays and the lower reaches. In summer, zooplankton differed from the spring zooplankton primarily by a considerable increase in the total biomass and by a decrease in the amount of rotifers in all parts of the reservoir. The decrease apparently is connected with the intense blue—green blooms. Numbers and biomass of zooplankton increased towards the middle of the reservoir and decreased in the lower reaches. In fall, the middle section and the lower reaches were dominated by cladocerans and copepods in equal numbers but the bed section was mainly dominated by nauplii and copepodites. In winter, c0pepods contributed about 70 percent of the entire zooplankton biomass. The population density of zooplankton of Lewis and Clark Lake showed two distinct peaks annually, one in late fall to winter months, another in late spring. The minimal values occurred in late summer and early fall. Both peaks were dominated by cyclopoid copepods, principally Cyclops bicuspidotus, which composed more than 60 percent of the annual standing crep. The calanoid copepods, nauplii, and Daphnia were found most abundant during the spring. In winter, c0pepods were mostly in the copepodite stages. The density of rotifers was maximum in June, and lowest in November (Benson and Cowell, 1967). They also found cladocerans and copepods were common at all depths in Lake Francis Case from late May to early July. Daphnia reached a maximum in early June with greatest density in the top 12 meters. Diaptomus was common throughout the year and reached a maximum in mid- June with the greatest density near the surface. Cyclops was abundant and more widely distributed from surface to bottom than other genera. Cowell (1967) reported that the zooplankton in Lewis and Clark Lake showed one pulse in winter under the ice and another in late spring to 78 early summer. Their density declined rapidly following the early summer pulse, and reached a minimum value in August. The population remained low during August and September, and then increased ten—fold during October and November. There was a unimodal peak in the Bull Shoals Reservoir with highest density in spring (Applegate and Mullan, 1967b). This contrasted with a newly created reservoir upstream (Beaver Reser- voir) which displayed a bimodal pattern with maximum 200plankton densities occurring in June and September. Yacovino (1970) investigated the abundance of zooplankton and its distribution in the Canton Reservoir, Oklahoma; he found the samples mainly composed of cyclopoid c0pepods, Diaptomus, Daphnia, Bosmina, Diaphanosoma, and Ceriodbphnia. The total quantities varied with horizontal location and depth. However, only Daphnia and Diaptomus showed a vertical layering, others occurring in about the same abundance at all depths. He found Daphnia and Diaptomus were dominant in spring; Bosmina was abundant in summer and fall. The distribution of zooplankton in the Goczalkowice Reservoir in Poland was reported by Mleczko (1968). He found rotifers dominant and distributed in the total vertical column in the spring. The distribution was usually distinctly stratified in summer with a maximum number of individuals occurring in the surface layer and much smaller numbers at the bottom. The greatest quantities in September and October were concentrated in the surface layer. In winter, low quantities showed an almost uniform distribution in the entire vertical water column. In India, Govind (1963) reported that the density of zooplankton in Tungabhadra Reservoir showed non-uniform yearly fluctuations. During his investigations from 1959 to 1961 he found two maxima of zooplankton occurred in March and August in 1959, two peaks in March-June, and in September 1960, and three peaks in February, June, and October of 1961. fr!“ 79 The copepodites and nauplii were abundant during March and September. Adult Cyclops was dominant during May and September, while adult Diap- tomus dominated from September to February. Benthos The bottom fauna in water bodies serves as an important source of food for fish especially for the benthophagic species. A knowledge of their development and species occurrence is necessary in the fishery management program of reservoirs, since they are directly influenced by the changes of physico-chemical and biological factors of newly created impoundments. Rzoska (1966) stated that a drastic decrease of benthos in the reservoirs occurred as a result of reducing currents. He found the rheophilic species were dying after 9 months of impoundment, when only 56 of 150 riverine species survived in the Mozhaisk Reservoir on the River Moskva, USSR. Grimas (1961) stated that the water level fluctuations caused a quantitative reduction of the bottom fauna in the impoundments in northern Sweden. He found a reduction of up to 70 percent in the zone of water fluctuations and 25 percent for the remain- ing areas. Schmulbach and Sandholm (1962) remarked that the retention time of impounded water was an important factor influencing the develop- ment of benthic fauna. He found a small standing crop of benthos in Lewis and Clark Lake was a result of a short period of retention time, the exchange of water through the reservoir taking about 8-10 days. Hruska (1965) pointed out that the construction of series of dams on a river caused a conspicuous decrease in the biomass of benthos of the reservoir downstream. He gave an example of the decrease in benthic biomass in the Slappy Reservoir in Czechoslovakia caused by the block- age of the river water upstream by newly created Orlik Reservoir. 80 Cowell and Hudson (1967) considered the water level fluctuations, depth, and water temperature as the major factors influencing the distri- bution and the abundance of the benthic animal (Hexagenia 8p.) pOpulation in Lake Francis Case, South Dakota. They also stated that a high rate of water discharge from the reservoir resulted in a significant loss of benthic invertebrates through the turbines. Petr (1968) found the distribution of benthos in the Volta Lake in Ghana was the result of oxygen deficiency. During the.stratification period they were pre- dominant in shallow waters and their abundance increased in deeper layers after heavy rains and during floods. This is a result of water column being oxygenated by the onset of rains and floods. Michael (1968) reported that a large number of benthic animals in the littoral zone were associated with the presence of aquatic plants. McLachlan (1969) found the presence of rooted littoral vegetation in Lake Kariba, Rhodesia, caused an increase in the biomass of benthic fauna. Craven and Brown (1969) investigated the benthic macro-invertebrates in Boome Lake in Oklahoma and concluded that the abundance of Chaoborus puncti- pennis increased with depth but decreased with silt depositions. Recently, McLachlan and McLachlan (1971) stated that the biomass of benthos was positively correlated with the amount of organic carbon in the profundal zone and inversely associated with the quantity of coarse sand in the littoral. They also stated that the development of permanent thermal stratification in the water bodies resulted in an absence of benthic animals in the profundal zone. Miroschnichenko (1971) reported that a sharp depletion of dissolved oxygen in the near bottom waters occurred during the period of summer stagnation in July—August. This condition resulted in decreasing larval population of chironomids in the Tsimlyanskoye Reservoir. Isom (1971) listed several factors that Uflmlhro fili- . v - rd 81 influence the abundance of benthos in one way or another, including siltation, rheotactile deprivation, water level fluctuations, hypo- limnetic oxygen deficiency, increased hydrostatic pressure, light intensity, and other impoundment associated conditions. The development of bottom fauna in newly created reservoirs varies greatly with environmental factors; however, they usually begin with Chironomidae, Oligochaeta, and Cladocera. Cowell and Hudson (1967) found the benthos of the limnetic region of Lewis and Clark Lake was dominated by Chironomidae (Diptera) larvae, and Hexagenia (Ephemerop- tera) nymphs, and also Oligochaeta, fingernail clams (Musculium), and Ceratopogonidae. Lake Francis Case was dominated by chironomids and oligochaetes, followed by Hexagenia, Ceratopogonidae and Chaoborus. Petr (1968) reported that the leading forms of Volta Lake in Ghana were chironomid larvae followed by nymphs of PoviZZa adusta. Snails (Bulinus) formed a substantial part of the total biomass of benthos in shallow areas with aquatic plants such as CeratOphyllum, Pistia, and Jusiae. These plants in some areas were occupied by larvae of caddisfly (Aethaloptera dispar). Paterson and Fernando (1970) made a remarkable report on the forma- tion of benthos in a new reservoir (Laurel Creek Reservoir) with par— ticular reference to the Chironomidae. They reported that at the time of first filling in the spring of 1967, the bottom fauna consisted of submersed terrestrial organisms, obligate, and facultative rheophilic species. Two months later, they found the substantial populations of colonizing limnophilic species developed in the habitat whereas the terrestrial and obligate rheophilic groups were lost. By the fourth month, the benthos was dominated by the euryoxybiontic limnophiles and by the facultative species. Prior to drainage in the fall of 1967, the 82 population densities of the euryoxybiontic chironomids declined while the polyoxybiontic species continued to increase in numbers. They concluded these changes were associated with the partial loss of the rich deposits of organic debris by siltation and decomposition. The survival of some limnophilic species after drainage produced an appreciably different pattern of colonization when the reservoir was refilled in 1968. During the second summer of the reservoir’s existence most euryoxybiontic chironomids further declined in abundance and were replaced by the polyoxybiontic forms. The facultative species originally derived from the creek fauna adapted to a wide range of environmental conditions in the reservoir habitat. Kryzanek (1970) reported that the formation of benthic communities in the Goczalkowice Reservoir on the River Vistula in Poland began with Chironomidae, and Oligochaeta. In the first year of the reservoir's existence, he found Chironomidae were the first group to populate the reservoir, followed by Oligochaeta. An intense growth of Tubificidae was observed in the second year and it continued to increase as the bottom sediments accumulated. Various species of snails were also encountered in the littoral zone during the first year in existence. The seasonal changes in the biomass and number of the bottom fauna in reservoirs are dependent on locality, the nature of the biological cycles of individual species, the effect of predation, and hydro- chemical conditions of impounded waters. Sokolova (1957) studied the seasonal changes of chironomids in the Ucha Reservoir in the Soviet Union. He reported that the number and total biomass of benthos at depths from 2-6 m decreased in summer, then increased in fall and winter. The maximum density of organisms was found in August, the maximum biomass in spring. The greatest biomass of chironomid larvae 83 of the profundal zone.was observed in early-late fall and in early spring. At other times of the year the biomass values were generally high exept for the first half of summer when the biomass dropped sharply due directly to the emergence in spring, and extended more or less to summer. There are many species of chironomids in the shallows; however, most of them are small in size and yield a small biomass even when pres— ent in large numbers. The actual biomass in summer was small due to the predation by fish. Miroschnichenko (1971) reported that the greatest number of chironomid larvae in the Tsimlyanskoye Reservoir usually occurred in the littoral zone, and decreased in number with depth. Only a few were found at the greatest depth. The larvae were concen- trated mainly in the central part of the reservoir and of former river- beds during fall, winter and spring. The summer minimum resulted from mass emergence of the adults, and also by being consumed by predators. In the tropical region, the benthic communities vary considerably in the littoral zone. Krishnamurthy (1966) studied the benthic macro- fauna at different depths in the Tungabhadra Reservoir in India. He found that mayfly nymphs dominated at 4 m, oligochaetes and bivalves at 24 m, gastropods at 10 m, and Diptera at 6 m in depth. The seasonal variations differed with species; he found gastropods dominated in April and November, bivalves dominated in May and October. Oligo- chaetes were the most dominant group in October, mayfly nymphs reached a peak in June and then disappeared in September to October. Diptera larvae were most dominant in August. Ichthyofauna The development of ichthyofauna in reservoirs is basically from the parental river and lake populations of the inundated areas. The 84 formation of the fish stocks is usually accompanied by a strengthening of the limnophilic species, and the suppression or complete disappearance of the rheophilic species. Tomnatik (1957) reported that the formation of fish fauna of the Dubossary Reservoir in the USSR showed the rheo- philic p0pulation decreased somewhat in the second year, while the limnophiles increased more than two—fold. A similar result was reported from Goczalkowice Reservoir, Poland, by Wajdowicz in 1964 (Figure 8). rheophilic 50 qbooooooooooo.... r/ SpeCieS l I t | . I I l 40 -1> 3O 7 . roach l 20 ‘--—-—--—-—.—J-°’ Jr’ ~‘.:t. | 0.. A / btenCh ... '... 10 _ ‘.. */4\’ ’0' a.- :h Zai- 20+.TQt—O&Oxi;*.:*.tw: 7:”- ... -00. ‘00.-..9- “. per Ch 0 ..‘I .001A41-nof AAAAAAAA I 19%4 1955 1d56 19§7 1958 1959 1965 Pre—impoundment fie. Post-impoundment Figure 8. Formation of the ichthyofauna in the Goczalkowice Reservoir, Poland. (From Z. Wajdowicz, 1964) In the United States, Kimsey (1958) stated that the native forage minnows such as Prychocheilus Zucius, Hesperoleucus venustus, Gila crassicaudo, and Mylopharodbn conocephalus, of streams in the Sacramento-San Joaquin and the lower Coloardo River areas were not able to maintain satisfactory populations in impoundments; many were reduced in numbers and some disappeared. Zhadin and Gerd (1961) noted that a change in fish populations in reservoirs usually began with a total loss of anadromous species especially in reservoirs that 85 did not have a fish passage. Then a decrease in species that spawn on a stony-gravelly bottom such as starlet, chub, asp, common savetta, and dace because the spawning grounds were destroyed by sedimentation. On the contrary, developing conditions in reservoirs were favorable to fish that breed in a slow current or in standing water, such as bream, roach, pike, and other limnophiles. Rzoska (1966) reported that there were only forty-seven out of seventy of the riverine species in the Dnieper Reservoir, and all of seven Caspian migrants completely dropped out in the lower Volga reservoirs after three years of impoundment. Denyoh (1966) investigated the changes in fish population in the Volta Lake in Ghana. He reported significant changes of fish pOpula- tions in the lake, some species which had not been caught in the early months began to appear, some species which dominated during the early period became reduced in number, and many species increased in abundance. He gave examples as Alestes sp. and Ctenopoma 8p. which were predominant in the early period and became rapidly reduced in numbers. At the same time, the Tilapia species (T. galibaea, T. nilotica, and T. zillii) increased in abundance and have become the dominant species in most areas. The Chrysichthys sp. which was caught in very small quantities in 1964 gradually increased in number in 1965 and became dominant in 1966. Fitz (1968) investigated a change in fish population of the pre- and post-impoundment of the Melton Hill Dam on the Clinch River. He found largemouth bass were absent in the pre~impoundment samples, but became abundant during the first spring of the impoundment. The crappie, bluegill, and white-bass increased in number after impoundment and showed a tendency to continue. The river herring was abundant in the first 86 year. Mooneye disappeared despite of numbers found in pre—impoundment habitats. Beckman and Elrod (1971) stated that following the closure of the Oahe Dam, a mainstream Missouri River reservoir in North and South Dakota, a number of riverine species began to decline in abundance and some disappeared. During the 5 years of.investigation,:they found only two young-of-year each of blue—sucker and shortnose gar, and none for pallid sturgeon, shovelnose sturgeon, paddle fish, and flathead catfish. Some lake—type species such as yellow perch, Perca flavescens, and emerald shiner, Notropis atherinoidss, were greatly increased in abundance. The development of fish populations in reservoirs may divide into 3 stages (Sharonov, 1966) as follows: (1) a rapid rise in abundance by the increase in growth rate and state of nourishment; (2) a sharp drop in growth of rheophilic species due toua reduction in growth rate and condition of the benthophagic fishes; and (3) an alteration of weak and strong year classes, the stabilization of growth, and an increase in abundance of low—value and course fishes. ~He described the first stage as connected with the filling period. The sharp rise in.abundance and growth rate was a consequence of better reproduction and feeding as well as high survival rate of young fish. The second stage resulted from a decline of benthos biomass and disappearance of the spawning grounds which in subsequent years exerted adverse effect on the abund- ance. The third stage presumed feeding conditions became relatively stable. The abundance of a stock was mainly determined by the water- level fluctuations, which disturbed both breeding and feeding conditions especially in species that spawn in shallow waters. The establishment of fish populations in reservoirs may take several years, depending primarily on the period of sexual maturation 87 of the species (Poddubuyi, 1968). He noted that a stock of.a given species will be completed whenever the brood stock consisted of the fish originated in.reservoir, rather than from the river origin. He cited the example of the fish fauna development in the Ivan'kovo Reservoir which was completed in the'ninth‘ year after the filling; that of the Uglich Reservoir was completed between the eighth.and ninth year; and that of the Rybinsk Reservoir was afterrllr12,years. Patriarche and Campbell (1958) found that success of spawning by all species of the Clearwater Lake in Missouri appeared in the fifth year of its existence. The year-class strength of fishes in the early stage of impound— ment is not only influenced by the fertility of water, inundated soils, food availability, and water-level fluctuation, it is also dependent upon the period of filling (Poddubuyi, 1968). He stated that if the reservoirs are flooded to the designated mark in one season, there would appear only one strong year-class of fish to live under initially favorable conditions. If the period of filling was extended over a few years and each year some parts of land were flooded which hitherto had not been inundated, then favorable conditions for a number of fishes would be maintained. During these years, the year- classes of the young are abundant. Therefore, during the first years, the fish stocks will develop in this type of reservoir better than in reservoirs that are filled in a single season. For example, the Ivan'kovo Reservoir was filled in one spring and there was only one very abundant year-class of bream. The Gorki, Kuibyshev, and Uglich reservoirs reached the designated level after two delayed spring floods, and the bream year-classes of the first two years were abundant. Il'ina and Gordeyev (1970) reported that the filling period of the Rybinsk 88 Reservoir took 7 years, and during these years the flooded areas increased each year. The newly flooded areas supplied additional nutrients to impounded water encouraging growth and reproductivity of the fishes; therefore the generations of these years were abundant to ensure maximum catches over a number of years. Bechman and Elrod (1971) stated that an annual abundance and distribution of a number of species in Lake Oahe during 1965-69 were affected by conditions created as the reservoir was filled and flooded new areas. They found the largest year-class of northern pike, carp, smallmouth buffalo, and bigmouth buffalo was associated with a rise and continuance of high water level in spring over terrestrial vegetation (primarily grasses). Small year-classes occurred in years when no new terrestrial vegetation was flooded. FISHERY MANAGEMENT The fishery productivity of reservoirs typically rises rapidly to the maximum within the first few years of their existence. The incre- ment is believed a result of better environmental conditions that favor the fishes. During the period of filling the reservoirs, the water leaches nutrients from newly inundated soils, submerged plant-debris and other organic matter. Therefore, the impounded water contains high fertility which encourages the growth of bacteria, phytoplankton, zooplankton, and benthos. These organisms-serve either directly or indirectly as food for fish; consequently, fish feeding on these organisms become more abundant as do also the predacious species which in turn feed on the small fish. Carlander (1955) noted that the fish production in reservoirs ranged from 2—8 times higher than in natural lakes. Pirozhnikov (1968) quoted the production of fish in the main Dnieper Reservoir as nearly 4 times greater than the annual catches from the unregulated Dnieper. Carter (1969) showed the biomass of fish populations of the inundated section of the Barren River had increased from an average of 111 lbs/acre/year before the impoundment to 194 lbs/ acre by the first year of impoundment. The second and third year of impoundment, the biomass averaged 201 and 241 lbs/acre/year respectively. Turner (1971) reported that the total sport fishing harvest in the Rough River Reservoir in Kentucky was higher than before impoundment. He demonstrated that the average number of fish harvested increased from 12 fish/acre before impoundment to 50 fish/acre in the first two years 89 . ., 3» gala, 90 of impoundment. Similarly, the average weight harvested increased from 3.5 lbs to 15.0 lbs/acre. Unfortunately, the high productivity of the reservoirs is not long sustained. It remains high only for-a year or more, then declines rapidly during the next few years to a much lower level which may be maintained or may gradually rise to somewhere near half the magnitude of the initial phase (Kimsey, 1958). The decrease is believed the result of: (l) the high initial fertility being largely leached out; (2) the organic matter, particularly the nitrogenous constituents in the submerged plant debris left in the basin, being removed by bacterial action, deposition, solution, and either being used in the'production of fish food or lost through discharges; (3) the loss by the nutrients being locked up in the bottom by sediments, which if rapid-may limit or reduce the bottom fauna in the deeper zones of the reservoirs because of unfavorable blankets of silt deposit; and (4) a large number of fishes and other aquatic animals which developed during the initial period of high productivity are now consuming the food organisms at a higher rate than the declining supply of basic food will support (Ellis, 1942). A decline in the fisheries in a reservoir is often followed by a recovery and stabilization at a new and lower level. This may occur whether or not any special management has been applied (Kimsey, 1958), because the fish populations and their food organisms are naturally adjusted to the permanent basic fertility of the basin and additional nutrients from—the inflows and watershed runoff. However, the produc- tive capacity will be different for each reservoir and will fluctuate from year to year in the same reservoir, depending upon its water supply and the Operations for other uses. 91 The objective of reservoir fishery management is ultimately increasing the yield and the maintenance of a fluctuating—harvest of the fish at a level near the optimum productivity of the reservoir. The production may consist of desirable species for either sport or commercial fishing purposes. Figure 9 shows thiS‘hypothetical goal of management practices in reservoir as recommended by Kimsey (1958). F“ u A ‘5 LH management goal \H .0 o a... Q) o .L'. .’. 4:0 ”-4 . .0 0.. . . .0 '0’. o g : «H ..o 0.. -H ’c. .c‘ C 0.4.. o H \ /v o o. .5 usual trend of g productivity 0 \J/ decline adjuéted’to new land effect recovery basic fertility Figure 9. History of a hypothetical reservoir fisheries. (From J. B. Kimsey, 1958) The solid line represents the usual production history of new impound- ments and the dotted line is the desired pattern. Management practices for smoothing fluctuations.of the fish populations and increasing yield are the manipulation of the habitats, the management of fish popula- tions and their food supply, and regulation of the fisheries. These activities based on sound data are essential for ensuring maximum pro— duction of fish. 92 MANAGEMENT OF HABITATS Fish production in reservoirs is usually considered secondary to other uses, hence impounded areas may not be favorable habitat for fish. The problems which may arise are associated with the spawning grounds, feeding areas, excessive growth of aquatic weeds and changes in species composition of the fish. These changes may either encourage or dis- courage the success of fishery establishment in reservoirs; therefore, modification or manipulation of the habitats may be necessary to prevent or reduce degradation of the fish populations or their food supply. Timber Clearing and Brush Shelters There has been much discussion about the degree to which reservoir basins should be cleared of timber before they are flooded (Hulsey, 1959; Burress, 1961; Davis and Hughes, 1971). Consideration includes the cost of clearing, the effect of clearning on fish pOpulations, food supply, and fishing Operations. Hulsey (1959) stated that there are many benefits to be derived from leaving large uncleared areas at elevations above the fish management pool. They include: (l).a sub- stantial saving in the total cost of a reservoir, as compared to complete clearing; (2) the timbered shoal areas will tend to reduce wave action from eroding the dam and shoreline; (3) the dead timber and litter will retard erosions when the shoal areas are exposed during drawdown; (4) the organic material will produce CO2 (from decomposition) which will help floculate the coloidal clay turbidity; (5) the standing timber, litter and debris will tremendously increase the surface area for attachment of periphyton and other organisms, thereby increasing the productivity of the reservoir; and (6) the timber areas will give a different type of fish habitat than the.open water areas. 93 The abundance of organisms on and in flooded trees varies with location, types of wood, the distance of trees offshore, and water turbidity (Petr, 1970). He reported that the abundance of Povilla nymphs, the most common organism in trees on the Volta Lake, were more dominant in the bark of trees than the.wood, and trees with harder wood were less attacked than those with soft wood. Aggus (1971) found the benthos in areas of recently flooded herbaceous vegetation of the Beaver Reservoir exhibited a higher rate of accumulation than in flooded trees and cleared areas. The reasons were the herbaceous vegetation provided more space for attachment, protection, and served either directly or indirectly as a nutrient source. The density of fish populations in flooded forests was investi- gated in many reservoirs by means of the fishing pressure and fishing success. Burress (1961) reported that the percentage of successful anglers in Bull Shoals Reservoir was higher in areas of flooded stand- ing timber (94.8%) than in open water (90.6%). The fishing pressure in 1959 amounted to 5,138 hrs/acre in timbered areas, as compared to 97 hrs/acre in the remainder. The hook and line harvest in flooded timber areas was 3,054 pounds/acre, and in the remainder areas was 113 pounds/acre. Davis and Hughes (1971) found the catchable size largemouth bass, Micropterus salmoides, and bluegill, Lepomis macro- chirus, in Bussey Lake, Louisiana, were more abundant in the flooded tree areas, while black crappie, Pomoxis nigromaculatus, and gizzard shad, Dorosoma cepedianum, were more abundant in open areas. In the USSR, studies of submerged forests were carried out on the Rynbinsk Reservoir (Poddubuyi, 1963). Fishing was done by means of standard "carpone" gill-nets with mesh of 12 to 70 mm, and also by "botalnye" nets. The highest average catch was recorded from the submerged 94 flood-plain forests, it was lower inshore protected by dead trees, and lowest in open water. Il'ina and Gordeyev (1970) stated that the presence of submerged forests near shore prevented organic matter from being washed out of the inshore zone. It promotes the mass development of plankton and other food organisms and created conditions conducive to the feeding of young fishes. Fish Passage The problems of passage and survival of anadromous fishes such as salmon, trout, sturgeon, alewives, smelt, striped bass, shad, and herring (Rounsefell and Everhart, 1953; Meehean, 1960) have become increasingly acute following the construction of the dams. The prob- lems are especially critical where the spawning runs are blocked from their spawning areas. It causes a failure in reproduction which results in decreasing recruitment to the stocks and finally reduces the catch. A number of structures have been built to enable fish to ascend dams to reach their spawning areas. These include fish-ladders of numerous designs, gravity locks, elevators and tank-truck transporta- tion (Sande, 1966; Eicher, 1970). The success of these devices depends on their efficiency in transporting the fish over the dams and deliver- ing them to a point from which they can continue their migration. This means a successful device must maintain runs of fishes at the same level of abundance existing prior to the construction of the dams (Royal and Cooper, 1960). The purpose of a fishway is to provide for the upstream or down- stream passage of fish past either a dam or a natural barrier. There- fore, it should be designed suitable for, and passable by, all the native migratory species, and with an attractive location of entrance 95 (Rounsefell and Everhart, 1953). To ensure success, they stated the entrance should be located close to the toe of the dam and close to the main current from the spillway or tailrace. The fish following the current will be led to the fishway entrance. It will avoid any delay upstream migration, and reduce any disturbance to spawning activity as a result of arriving late in their spawning areas (Somme, 1960). Furthermore, the slope of the fishway, and velocity of flow, are also recognized as important factors to influence the upstream migration. Experiments showed that the fishway with a slope steeper than 1 on 16 (a rise of 1 ft for every 16 ft long) up to l on 8, and a velocity of 2 fps, were suitable for passing salmonids (Collins and Elling, 1960). Detail of different types of the fishways and their operation is beyond this study; for further descriptions see Rounsefell and Everhart (1953), Clay (1961), and Eicher (1970). The fish locks are applied to sites that offer little space for a fishway or where the lift is so high as to preclude the use of a conventional fishway. They have been used much more extensively in Europe, such as in The Netherlands (Deelder, 1960), than in North America (Baker, 1966). Many areas have used a fish lift or elevator for passing the fish upstream. An elevator consists of a tank or hopper which fish enter and which is then hoisted mechanically to the stream above the dam where the fish are released. In some instances, methods such as the above have been impracticable either becuase of mechanical difficulties or the exorbitant expense of construction. The fish may be trapped and then transported by tank-trucks to release points above the dam, or even to other streams (Dill and Kesteven, 1960). 96 The problem of ensuring the safety and free passage of downstream migrants, both young and adult, over, through, and around dams is as important as the problem of passing upstream migrants. Probably more ingenuity has been applied to provision of devices for passing fish downstream past obstructions than has been the case in upstream passage (Eicher, 1970). Many factors arise in reservoirs that may seriously affect the downstream migration such as oxygen deficiencies, high water temperature, and slow currents (Trefethen, 1968).' Research aimed at finding means Of ensuring adequate downstream migration has been investigated and some.feasible methods recommended (Eicher, 1970). Although many fishways and other devices for guiding and passing fish over, through, or around dams have been successful, the installa— tion of the fishways or other means is no guarantee that the run will be preserved. Many fishways built in tropical African impoundments have failed to be used by migratory fish (Jackson, 1966). Many species of native tropical fish will readily ascend the fishways and enter the impoundments for either spawning or feeding. Such are Labeo altivelis, Barbus viviparus, Tilapia sparmanni of North Rhodesia (Bell-Cross, 1960), and Hilsa ilisha of the Indian River in Madras State (Hickling, 1961). Since fish passages are often expensive to build and Operate, it should be kept in mind that they are needed only where fish of economic value are known to make regular and necessary migration to spawn, and when its interruption will seriously affect the fisheries. Designing, construction and operation of the fishways require close cOOperation between designers and fishery biologists. 97 Artificial Spawninnground The availability of spawning grounds Often becomes the main limit- ing factor on fish populations in reservoirs after they have.been in existence for a few years. Parts of initial favorable spawning areas are destroyed either by sedimentation or by water level fluctuation. Regulation of a river discharge by the dam seriously affects the repro- duction of the migratory species such as trout and salmon as a result of blocking their ways to spawning grounds. It has appeared that the construction of Grand Coulee Dam on the Columbia River has shut off the sockeye, Onchorhynchus nerka, migration to spawning areas in the upper Columbia River above the confluence of the Okonagan River (Clay, 1960). This situation leads to a reduction of reproductive success, to a decline in the abundance of the year-classes, and to a decrease in catches. Improvement in existing spawning grounds for valuable species in reservoirs and on the rivers downstream from the dams is necessary for increasing the fishery production. Alteration of the habitats to provide spawning facilities deserves intensive attention as a_manage- ment technique. A number.of investigators have created artificial spawning grounds and observed the use of them by certain species such as the salmonids. Hourston and MacKinnon (1957) reported their experi- ment on the use of artificial spawning channel in Jones Creek, British Columbia, which was built to replace natural spawning ground that was lost to the hydro-electric development on the stream. They claimed this artificial channel was used by the salmonids for spawning in the first few years prior to encounter with sedimentation problem. Prevost (1957) reported that the artificial spawning beds for lake trout, Salvelinus namaycush, made of sharp rocks were better than natural 98 spawning beds composed of round boulders. He stated that eggs laid in the interstices between sharp rocks were protected to a certain extent against depledation by other fish, while eggs laid on round boulders were easily reached by predators. Webster (1962) applied two procedures to improve the natural spawning facility for brook trout, SthZinus fOntinaZis, in waters of the Adirondack Mountains, New York. The methods were: (1) a replacement of unsuitable bottom material with washed gravel on or near known natural spawning areas; (2) piping and dispersing water through a gravel-filled box. He reported that both types of improvements were used by brook trout under acceptable environ- mental conditions (e.g., water depth, gravel size, and water temperature). A number of reports have been found in the Soviet Union's litera- ture. Sukkoi Van (1959) set up an experiment on artificial spawning grounds in the Dnieper River, below the dam of the Kakhovka Hydro- electric Station, by using artificial nests. The nests were built with a substratum of forked roots of various plants. He found as many as 90 percent of the nests were used by Azov roach, Rutilus rutilus heckeli. Nezhivenko (1969) used artificial shrubs to create spawning fields in reservoirs, the shrubs raised above the bottom by about 1.5 m, to prevent silting over and to permit being washed off by wave action. Khoroshko and Vlasenko (1970) reported that three experimental stone- gravel beds were constructed on the Volga and the Kuban' to provide conditions favorable for natural spawning of sturgeons that approached the dam. The spawning grounds were constructed of gravel of medium size category (5-10 cm) with a small admixture of chippings. The spawning substrate was deposited during the low-water period along the dry slope of the bank. The artificial beds were 10-12 m wide, 1,000 m long, and 30 cm thick. The two years of observations on the use of these 99 spawning grounds by sturgeons showed they were less significant in the Volga than in the Kuban' River. Control of Aquatic Vegetation The blooms of algae and intense growths of higher aquatic plants in reservoirs Often produce undesirable changes. They may interfere with, and compete for, a variety of uses of impounded water, such as fishing, hydro-electric power generation, irrigation, and boating. They also increase water loss by transpiration, reduce the productive capacity of the impoundment, and provide excellent breeding grounds for many disease-carrying and nuisance-causing insects (Little, 1969). Control- ling aquatic weeds has become a serious problem in reservoir management. A number of controlling methods are continuously being developed for more effectiveness and success. The control may be done either by a mechanical, chemical, or biological method depending on the nature and scope of the problem, type and extent of the control desired and comparative costs. (1) Mechanical Control The mechanical methods of controlling aquatic vegetation can be applied by several ways, such as filtration or screening, hand-pulling and cutting, raking, chain dragging, and by power-driven underwater weed cutting and weed removal units. The application of these methods depends on field condition, the extent of control desired, labor and cost involved. Advantages of the mechanical control are: (1) it does not introduce foreign substances into the water; (2) it may actually remove nutrient materials from the lake cycle, and should tend to reduce the rate of lake filling by plant residues; (3) if carefully done, it probably does not tend to alter the plant and animal life lOO balances; and (4) it can provide immediate relief from nuisance condi- tions (Livermore and Wunderlich, 1970). During the blooms, algae may be removed by filtration or screening. Mackenthun and Ingram (1967) reported that the microstrainer is very efficient in removing these algal cells occurring in chains. They found the strained water contained only single cells or chains of 2 or 3 cells in length. However, the harvesting of algae by this method is impractical because of their minute sizes and their wide horizontal and vertical distributions throughout the water bodies. Raking is the only way at present to remove filamentous algae (Fryer and Makepeace, 1970). Scythes and sickles for cutting are widely used to clear rooted plants from small areas. A weed saw consisting of a long steel handle can be used to cut fairly sizable areas around beaches and docks. Forking and raking following mechanical cutting or for general shore- line cleanup of weeds and debris is still probably the most widely used collection method (Livermore and Wunderlich, 1970). Cutting by hand is laborious work which is only employed for small areas where the use of motorized machines is not practicable. A number of mechanical weed- cutters have been developed. Various types of saws, crushers, and chOppers have been used to destroy aquatic vegetation, particularly water hyacinth and alligator weeds. Knife-type cutters, which are dragged through the plant beds and cut by scything action, have been used for cutting both submerged and emergent plants. A continuous chain-type cutter carrying sets of moving blades over stationary shearing knives has been used on some recent models of aquatic weed harvesting machines. Chaines and draglines are often pulled along the bottoms of waterways behind powerboats as a means of uprooting lOl vegetation. Even though machinery can and will destroy the aquatic vegetation, it must be clearly recognized that all mechanical devices have their individual limitation. To date, there still is no machine with all the requirements for a large scale operation. (2) Chemical Control The effect of herbicides on plants varies from one chemical to another. Many herbicides control several to many species within either the submergent or emergent groups; others control plants in both these categories with varying effectiveness. Some chemicals will control higher aquatic plants and algae as well (Zajic, 1971). Mackenthun, Ingram, and Porges (1964) state that effective algicides or herbicides used in water must: (1) be reasonably safe to use; (2) kill the spe- cific nuisance plant or plants; (3) be nontoxic to fish, fish-food organisms and terrestrial animals at the plant-killing concentration; (4) not prove seriously harmful to the ecology of general aquatic area; (5) be safe for water contact by humans or animals, or provide suitable safeguards during the unsafe period; and (6) be of reasonable cost. Some of these factors assume added significance, based primarily on the physical aspects of a particular control operation. Chemical control has proved the most economical and effective means of rapidly eliminating certain plant species (Montgomery, 1965). Its principal advantages include: ease in application, lasting effect, and covering of large area in a short time in application (Mackenthun and Ingram, 1967). It may be used in conjunction with mechanical con- trol for areas where mechanical methods are impossible or impractical. Sometimes it may be applied in advance to prevent a nuisance problem or to suppress a particular species (Livermore and Wunderlich, 1970). 102 The application of herbicides to aquatic weeds is usually by spraying on the foliage of weeds in case of floating and emergent plants. Spray may be applied from the banks, boats, or even from the airplane, depending on characteristics and areas covered by aquatic weeds. In this case, the manufacturer's instructions should be followed exactly concerning the percentage solution required to provide effective control. The application of herbicides for submerged plants and algal control has to be introduced into the water to form a dilute solution. To determine the amount of herbicide to be added to water to obtain the required concentration, the weight of water should first be calculated as follows: Weight of total volume of water in pounds = Area in sq.ft X average depth in ft X 62.3 The amount of herbicide to be added is then determined by the equation: ppm X lb of water 1,000,000 pound of herbicide = Furthermore, Fryer and Makepeace (1970) recommended that it is often quicker and more convenient to calculate the volume of water in acre-feet (i.e., area in acres X average depth in feet). They stated that since an acre-foot of water weighs a little over 2,700,000 lbs, therefore an addition of 2.7 lbs herbicide per acre-foot will provide a concentration very close to 1 part per million. The use of chemicals for controlling aquatic weeds.must not only produce the fastest kills, it must be safe to fish and fish—food organism also. The effects of aquatic herbicides on fish may derive mainly from direct toxicity to fish or indirect effects such as deoxygenation caused by decomposition of killed weeds. Fortunately, it appears that acute 103 toxicity of herbicides to fish is at higher-concentrations than those used for weed control. For example, the TLm-values of dichlobinil for fish varies from 10-30 ppm while 1.0 ppm is effective in controlling aquatic weeds in stagnant water (van Busschbach and Elings, 1967). Silvo (1967) also reported that the common carp 6 months old can tolerate up to 20 ppm of paraquat, while a concentration of 0.5-1.0 ppm was a very good control of Elodea canadensis. Moreover, Swan (1967) pointed out that the margin of safety that may exist for a herbicide used in controlling water weeds depends not only on its toxicity, the concentration at which it is effectively phytotoxic, and metabolism in animals, but also depends on its rate and mode of disap- pearance from water. He stated that the rate of disappearance of herbicides from treated water is affected by some variables such as the nature of the vegetation, the amount of dilution by water flow, the nature of the bottom soil, and.the amount of agitation after appli- cation. A maximum period of 3-4 weeks is recommended as necessary for 2,4-D and dalapon to decline to about one-hundredth of their initial level. In this respect, he found some herbicides such as bipyridylium compounds, paraquat, and diquat have the advantage that they are absorbed by weeds and adsorbed to soil which leads to their rapid disappearance from water. Sewell (1970) reported that the residues of diquat fell below detectable levels between 4 and 8 days after a cove treatment with 2 gallons diquat per surface acre in Findley Lake, and between 0 and 1 day in Chautauqua Lake. The latter was a typical perimeter treatment of a large lake with the same rate of application. Silvo (1967) found the concentration of paraquat in the water was reduced from 0.1-1.0 ppm to less than 0.001 ppm in, at the most, 5 days after treatment. 104 a. Control of Algae Algal control treatments can be marginal or complete; the type applied to a given body of water must be determined by the size, shape, and relative fertility of the water, and the estimated cost of the project (Mackenthun and Ingram, 1967). Marginal treatment refers to a method designed to obtain temporary relief in a restricted area where more extensive activity is not feasible or financially possible. In this procedure a strip, 200 to 400 ft wide, lying parallel to the shore, and all protected bays are sprayed.. No other part of the area is treated even though much algae may be present. On the.other hand, complete treatment is applied over the entire surface area of a water body. It insures that a major portion of the total algal.population is eliminated, so that it requires a longer period to recover. The interval between necessary treatments will be directly correlated with climatological conditions and the available nutrients released from dead algal cells. One to three complete treatments per season may be sufficient to give reasonable control. Zajic (1971) suggested that algae and rooted submerged plants should be treated during the spring or early summer while the plants are developing and before they reach nuisance levels. During this period, the chemical will provide more effective control of the plants and there will be less problem of oxygen depletion as a result of decomposition of a large algal mass. Funk and Gaufin (1965) reported that the effectiveness of indi- vidual algicides in Deer Creek Reservoir appears to be the result of several variable conditions. They listed some of the most obvious of these variables as the following: (1) organic enrichment of storage water supplies that is necessary to growth of algae; (2) excessive alkalinity interferes significantly with the solubility of most 105 algicides. Field investigations showed that most effective algicides were rendered useless in water with a total alkalinity of over 300 ppm; (3) varying temperatures stimulate seasonal blooms and algal succession; increasing temperatures may enhance the capabilities of some algicides, such as dichlone; (4) extremely resistant algal species do not appear to respond to strong algicides even under favorable conditions. Therefore a dosage required for controlling depends upon the chemistry of the water, the toxicity of algicides, as well as the susceptibility of par- ticular organisms. The results of algal control by using different algicides are summarized in Table 2. b. Control of Floating and Emergent Aquatic Plants These two kinds of aquatic plants are considered jointly, because of similarity in control methods. Many of these plants have waxy coating on their leaves which resists penetration of chemicals unless oil carriers or sticker—Spreaders are used. Surber (1961) stated that one of the most effective, economical, and safest herbi- cides for control of these aquatic plants is 2,4—dichlorOphenoxyeacetic acid (2,4-D). It is a growth regulator type of weed killer which is absorbed by affected plants and translocated to all of their parts. Plants affected by this chemical may grow themselves to death, or simply wilt and die from the toxic effects. This herbicide has been used in liquid either in kerosenes, household detergent, and in other organic chemicals, such as in formagens, for the control of these aquatic plants. Other herbicides are also widely used; the results of their effectiveness are summarized in Table 3. 106 Table 2. Some herbicides and their effectiveness in controlling algae Algicides Rate to kill Name of algae References Algaecidex 1.0 ppmw*(Cu804) phytoplankton Hiltibran, 1970 Atrazine 0.2 ppmw filamentous Hiltibran, 1970 Copper sulfate 0.3-0.5 ppm Surber, 1961 (soft water) blue-green 1.0 ppm and (hard water) green Cutrine 1.0 ppmw (CuSO4) filamentous, Hiltibran, 1970 phytoplankton Dichlobenil 4 lb/A Chara vulgaris Hiltibrain, 1970 1.0 ppm Vaucheria van Busschbach & Eling, 1967 Dichlone blue-green, Funk & Gaufin, green, 1965 diatoms Diquat 1.0 ppm Cladophora Jennings, 1967 Diuron l lb/A filamentous Hiltibran, 1970 0.1 ppm filamentous Bungenberg de Jong, 1967 Pennsalt TD-47 diatoms Funk & Gaufin, 1965 Pennsalt TD-l88 green, diatoms Funk & Gaufin, 1965 Pennsalt TD—l9l diatoms, green Funk & Gaufin, 1965 Paraquat 0.5-1.0 ppm phytoplankton Silvo, 1967 Simazine 0.2-0.4 ppmw filamentous, Hiltibran, 1970 phytOplankton * ppmw = part per million by weight Table 3. 107 and emergent aquatic plants Some herbicides and dosages recommended to control floating Herbicides Rate to kill Name of plants References 2,4-D, acetamid (20Zact.ingr.) 2,4-D, amine 2,4-D, ester D, granulated S-T 2,4- 2,4- 2,4 Amitrole Amitrole formu- lation Dalapon Dichlobenil Diquat Endothall Diuron Paraquat Silvex 10 lbs/A 100 lbs/A 5 lbs/A 1000 ppmw 10 lbs/A 2 lbs/A 10-20 lbs/A 1.0 ppm 0.5 ppmw 0 ppm lbs/gal 5-l.0 lbs/A 0 ppmw 1. 2 0. 2. 8 lbs/A 3 lbs/A needlerush pickerel weed, burreed, water-hyacinth, arrow— head cattail, pickerel weed, lotus, alligator weed, softstem bulrush, needle- rush, parrot-feather, water lettuce, water shield, white-water lily, spatterdock, burreed, arrowhead water shield cattail water-hyacinth, Pistis, Spirodela, Ipomoea cattail water-hyacinth cattail, cutgrass, Manna grass Phragmites communis, Acoms ca Zamus HydriZZa verticillata Callitriche stagnalis duckweed Chara, water primrose HydriZZa verticillata alligatorweed softrush Surber, 1961 Surber, 1961 Surber, 1961 Surber, 1961 Surber, 1961 Misra & Das, 1969 Surber, 1961 Gallagher, 1962 Surber, 1961 van Busschbach & Eling, 1967 Mackenzie & Hall, 1967 Surber, 1961 Bennett, 1970 Blackburn & Weldon, 1970 Weldon &) Durden, 1970 Surber, 1961 108 c. Control of Submerged Plants The chemical control of submerged plants has been investigated as much as the others. Many chemical substances have been tested for this purpose. Surber (1961) reported that sodium arsenite is.a cheap and very effective chemical for controlling nearly all species Of sub— merged aquatic plants. Smith and Hall (1967) found that applying butoxyethanol ester of 2,4—D in a 20% granular form was most effective control of Eurasian watermilfoil, Myriophyllum spicatum L. Jennings (1967) reported that a concentration of 1.0 ppm of diquat was extremely effective against certain underwater weeds such as Elodéa canadénsis, Pbtamogeton spp., etc. Newman (1967) stated that the application of paraquat or diquat to water at rates Of from 0.5 to 1.0 ppm will kill most submerged weeds. The treatment had no direct toxic effect on fish or on invertebrates in water. The applied herbicide was removed from the water rapidly, and was ultimately destroyed by microbiological breakdown, or was inactivated by adsorption in the bottom mud. The results of application of some common herbicides on submerged plants are summarized in Table 4. (3) Biological Control Biological control is considered as the most feasible method in controlling aquatic weeds in areas where the cost of chemical or mechanical control is prohibitive. Mulligan (1969) stated that the biological control is the only method that could provide a permanent solution to the problem of excessive aquatic vegetation. It usually results in relatively low costs, ready supply sources, ease of applica- tion which often requires no special equipment, minimal training of ~ unskilled personnel, and relative permanence of treatments with an 109 Table 4. Some herbicides and dosages recommended to control submerged aquatic plants Herbicides Rate to kill Name of plants References 2,4-D, ester (20% granular) Copper sulfate Diquat Diuron Endothal (granular) Hydrothol Hydrothol 191 (granular) Paraquat Silvex Simazine Sodium arsenite 20-40 lbs/A 100 lbs/A 0.5-1.0 ppm 1.0 ppm 2 gallons/A 0.5-1.0 lbs/A 2.0 lbs/A 3.0 lbs/A 4.0 lbs/A lO lbs/A 2 05-4 00 ppm Eurasian watermilfoil Elodba dbnsa most submerged weeds Elodsa canadbnsis, CeratophyZZum demersum, Potamogeton spp., Hydrocharis morsus-rcmae, E. dansa water milfoil black willow, coontail, naiads all above, plus lotus, pond weeds all above, plus curly- 1eaf pondweed, rushes, water smartweed all above Potamogeton diversi- beius P. pusiZus .P. emericanus P. beiosus southern naiads Elodaa spp. most submerged weeds E Zodea ccmadens is white water-lily yellow water-lily water weed, mud plantain, water milfoil, bladder- wort P. diversifblius most submerged weeds Smith & Hall, 1967 Ware, 1966 Newman, 1967 Jennings, 1967 Sewell, 1970 Dalrymple, 1971 Dalrymple, 1971 Dalrymple, 1971' Dalrymple, 1971' Surber, 1961 Surber, 1961 Surber, 1961 Frizzell, 1962 Ware, 1966 Newman, 1967' Silvo, 1967 Younger, 1958 Younger, 1958 Younger, 1958 Surber, 1961 Surber, 1961 110 ability to resist weed reinfestations (Butler, Ferguson, and Barrios- Duran, 1968). The success of this method of controlling has been accomplished mainly by the use of insects, snails, fishes, and manatees as the controlling agents. (a) Insects Insects are one of the most effective biological control agents. They may kill their established host plants either directly by destruction of photosynthetic tissue, or indirectly by causing depletion of the food reserves. The essential characteristics of an insect as a biological control agent include: (1) the ability to kill aquatic vegetation or prevent its reproduction in some direct or indirect way; (2) an ability to disperse and locate its host plant; (3) an adaptability to weed host and to environmental conditions in which it occurs; (4) a reproduction capacity sufficient to overtake an increase of its host plant; and (5) host specificity to prevent damage to desirable plants (Blackburn, Sutton, and Taylor, 1971). The most outstanding example of an insect controlling aquatic vegetation is the flea beetle, Agasicles sp., on alligatorweed, Alternanthera philoxeroides (Mart.) Griseb. This insect was intro— duced to the United States from Argentina in 1964 (Hawkes, 1965); since then, the flea beetle has become established throughout most of the region infested by alligatorweed, particularly in the southeast states. This insect feeds only on alligatorweed. Blackburn, Sutton, and Taylor (1971) found the beetle population declined rapidly after the alligatorweed leaves tun! been eaten, and the flea beetles were then forced to eat the stems, and/or move to other areas. Sailer (1972) reported that the stem-boring moth, Vogtia malloi Pastrana, is 111 also an effective controlling agent on alligatorweed. Laboratory studies showed that the damage caused by the moth—larval feeding was more injurious to alligatorweed than that of the flea beetle. It also appears that the moth is an effective enemy of alligatorweed in more northern areas where the beetle has failed to overwinter. The moth was found either to attack the weed where it grows in rooted mats or at terrestrial sites, neither of which habitats are favorable to the beetle. Furthermore, he found the adult of weevils, Neochetina.spp., feed on water-hyacinth leaves, and their larvae tunnel in the.stem and: root crown of this plant. It seems possible to use them as a.control- ling agent on water-hyacinth. To date, the weevils are under experiment by the Agricultural Research Service Biological Control of Weeds Labora- tory at Albany, California. Another interesting experiment is a control of floating fern, Solvinia auriculata Aubl., by using Wingless aquatic grasshoppers, Paulinia acuminata (Blackburn, Sutton, and Taylor, 1971), but control still has been accomplished only at the laboratory level. Information on insects that feed on submerged plants has been obtained. The larvae of the moth, Paropoynx stratiotata (L.), clearly prefer to feed on Eurasian watermilfoil, Myriophylum spicatum,.and also feed to varying degrees on other submerged aquatic plants (Sailer, 1972). He also reported that two weevils of the genus Bagous feed on Florida elodea, Hydkilla verticillata (L.F.) Casp. However, no detail of the success in controlling submerged plants by using insects has been reported so far. (b) Snails The investigation of a large tropical freshwater snail, Marisa cornuarietis L., for the biological control of aquatic weeds was begun 112 in 1961 at Fort Lauderdale, Florida (Blackburn and Weldon, 1965). Seaman and Porterfield (1964) reported that this snail attacked a variety of submerged aquatic plants with complete control of coontail, Ceratophyllum demersum L., southern naiad, Najas guadalupensis (Spreng) Magnus, Illinois pondweed, Potamogeton illinoensis Morong, and partial control of water fern, Pistia stratiotes, and alligatorweed, Alternantera philoxeroides. Water-hyacinth, Eichornia crassipes, was not completely eaten; however, its growth and flowering were greatly retarded by root pruning action of the snails. Marisa preferred submerged weeds to float- ing or emersed weeds, but the floating weed, Salvinia rotundifblia Wild., was eaten nearly as readily as submerged weeds. The problem of using Marisa in controlling aquatic vegetation is that they will eat young rice plants when other food is not available. This feeding behavior has prevented the release of this snail in rice growing regions of the world (Butler, Ferguson, and Berrios-Duran, 1968). Another species of freshwater snail that shows promise as a biological control of submerged vegetation is Pomacea australis d'Orbigny. This snail is native to northern Brazil. The preliminary experiments shows that the snail fed on many aquatic weeds, even more vigorously than does Marisa (Blackburn, Sutton, and Taylor, 1971). (c) Fish Many herbivorous fishes have been used as biological control agents for aquatic vegetation. These fishes may limit the growth of aquatic weeds either by ingesting the plant tissue or by stirring the hydrosoil to increase turbidity which inhibits light penetration and thus reduces photosynthetic activity (Blackburn, Sutton, and Taylor, 1971). They listed the fishes that appear to have promising potential 113 in controlling aquatic weeds include: The Congo tilapia, Tilapia melanopzeura Dumeril; Java tilapia, Tilapia mossambica Peters; Nile tilapia, Tilapia.nilotica L.; Tilapia ziZZii Gervais; Grass-carp, Ctenqpharyngodon ideZZa Val.; Silver dollar, Metynnis roosevelti Eig.; Silver dollar, Mylossoma agrenteum E. Ahl.; Common carp, Cyprinus carpio L.; and Israeli carp, Cyprinus carpio L. (Israeli strain). Other species which have been tested and appear to have value include: Silver carp, Hypophthalmichthys molitrix (Va1.) (Prowse, 1969); Carp, Puntius sp., and Osteochilus hasselti Cuv. & Val. (Hora and Pillay, 1962); Carassius carassius L. (Swingle, 1957); Osphronemus sp., Alestes macrophtalmus Gunther, and Distichodus sp. (Hickling, 1961); Channel catfish, Iotalurus punctatus Rafinesque, and Goldfish, Carassius auratus L. (Avault, 1965); and Mugil sp. (Grizzel and Neely, 1962). The Congo tilapia feeds mainly on plankton, filamentous algae, and higher aquatic plants. Maar (1960) reported that the Congo tilapia effectively controlled both submerged and floating plants in reservoirs in southern Rhodesia. Investigation showed that their stocking rates in ponds of approximately 1,500 to 2,000 per acre could control Pithophora sp.; Spirogyra sp.; EZeocharis acicularis; EZOdea dense; Hydrochloa sp.; Utricularia biflora; and Rhizoclonium sp., in 3 months (Avault, 1965). Pierce and Yawn (1965) reported that the Congo tilapia and the Nile tilapia are excellent control of filamentous algae and submerged vegetation where these fishes can winter-over and are stocked alone or allowed to become well established prior to the stocking of bass. The planting of both Congo and Java tilapia in Puerto Rico resulted in control of Spirgyra, Chara, Najas, Nitella, and some surface plant covers (Butter, Ferguson, and Berrios-Duran, 1968). The stocking 114 of Tilapia aurea in reservoirs in Israel resulted in a significant decrease in the amount of filamentous blue-green algae and submerged vegetation (Eren, Yashouv, and Langer, 1972). In.Malacca, Prowse (1969) reported that Tilapia ziZZii eat most aquatic vegetation except the most woody water—weeds. However, bigger fish apparently are quite able to control the coarser sedges, possibly by uprooting them when the fish build their nests. He also stated that this species feeds on some floating plants such as Lemna and Spirodella. In Africa, an introduction of Tilapia macrochir into Lake Kariba was as an algal controlling agent (Jackson, 1960). The grass carp appears to be one of the most promising herbivorous fish for controlling of rooted aquatic vegetation (Swingle, 1957). In general this fish prefers soft vegetation and will eat more than its own weight daily of such plants as pondweeds, coontail, and duckweed (Cross, 1969). His eXperiments showed the preference for some aquatic plants by the grass carp as presented in Table 5. However, feeding may be interrupted by abrupt changes in temperature and by the ripples pro- duced by wind, making it difficult to assess food selectivity QAlabaster and Stott, 1967). They claimed the feeding becomes less selective as its intensity increases with increase in temperature up to 25° C and also as the total supply of food and variety of species is reduced. In ponds, the grass carp controlled Chara sp., Potamogeton diversifolius, and Eleocharis acicularis in 1 month when the fish was stocked at a rate of 20 to 40 per acre (Avault, 1965). He also reported the results of experi- ments of using Israeli carp (6 to 9 inches in total length) when stocked at rates of 25 to 50 per acre were effective in reducing or eliminating Pfithophora sp., Rhizoclonium sp., and Eleocharis acicularis. Further- more, he found channel catfish can reduce or eliminate Pithophora in 115 Table 5. Aquatic plants eaten by the grass carp, Ctenopharyngodon idellus Val., in approximate order Of preference (From D. G. Cross, 1969) Order of preference Common name Scientific name 1 Canadian pondweed Elodea canadensis Michx. 2 Hornwort, coontail Ceratophyllum demersum L. 3 Stonewort Chara 6p. 4 Lesser duckweed Lemna minor L. 5 Broad-leaved pondweed Pbtamogeton natans L. 6 Ivy-leaved duckweed Lemna trisulca L. 7 Watermilfoil Myriophyllum sp. 8 Fermel—leaved pond- Pbtamogeton pectinatus L. weed 9 Common cattail Typha Zatifolia L. 10 Common reed Phragmites communis Trin. 11 Common rush Juncus efyhaus L. 12 Black sedge Carer nigra L. 13 Frogbit Limnobium spongia (Bosc) Steud. l4 Watercress Nasturtium officinale R. Br. 15 Shingy pondweed Potamogeton Zucens L. 16 Sedge Carer pseudocyperus L. ponds when stocked at a rate of 1,000 per acre, but were not effective when stocked at a rate of 200 per acre. Goldfish also gave good control of Ptthophora when stocked in ponds at a rate of 685 per acre. Blackburn, Sutton, and Taylor (1971) reported that Silver dollar fishes such as two species from South America, Metynnis roosevelti and MyZossma argenteum, appeared to have great potential as biological control agents. These fishes graze on horned pondweed, Zannichellia palustris L., American pondweed, Pbtamogeton nodosus Poir., and sago pondweed, Potamogeton pectinatus L. (Yeo, 1967). He also remarked that the Silver dollar fishes prefer new growth plants to older plants. 116 (d) Manatee The manatee, Trichechus spp., is widely distributed in the Atlantic Oceanic areas. This animal is quite capable of living both in freshwater rivers and in a completely marine environment (Allsopp, 1969). The manatee feeds on various types of aquatic plants, whether marine or freshwater species. He stated that the experiments conducted in Guyana (British Guiana) showed the animal ate many species of aquatic plants, such as Chara, Myriophyllum, Potamogeton, Ceratophyllum, Eichhornia, Nymphaea, Nelumbo, Salvinia, Pistia, Montrichardia, Typha and others. He also stated that the manatee feeds very systematically, eating first the luscious, submerged plants and then the less attractive and more fibrous floating or emergent plants. Generally, the animal in its natural environment prefers to feed on the submerged plants, the young shoots and new leaves of the floating and emergent plants rather than the older and harder vegetation. The use of manatee as a means of water-weed control is far more effective and lasting than the usual chemical controls (Allsopp, 1960). It had been found that two manatees sizes 7-1/2 ft long were capable of clearing a canal 22 ft wide and 1,600 yd long in 17 weeks. Sguros, Monkus, and Phillips (1965) reported that the use of one male and 4 female manatees ranging in weight from 350 to 2,000 pounds and.being up to 12 ft in length could eat the submerged weeds in one-half mile of canal navigable with almost normal water flow in about one week. Blackburn, Sutton, and Taylor (1971) claimed that an experiment using the same weight of manatees could clear the same canal infested with water-hyacinth in 8 weeks. After the canal was cleaned of submerged and floating weeds, the manatees began to eat the bank vegetation that extended into the canal water. They also stated that the canal was 117 freed of vegetation for 6 to 8 months after the manatees were removed. The manatee is harmless to fish and other aquatic animals. Its capability appears as a feasible means of controlling aquatic weeds particularly in areas where other means are impractical such as that in British Guiana's water canal. However, the successful use of this animal as a biological control agent needs further study especially of its reproduction and propagation. FISH POPULATION STUDIES Fish populations in reservoirs usually increase rapidly in numbers and mass after filling; thereafter fluctuations occur seasonally or from year to year. The fluctuations relate to the biology of the species and to the effects the vagaries of environment have on abundance and distribution. Therefore, knowledge of these changes is necessary in order to improve long term forecasts, to plan catches, and to develop rational ways of fishing and of conserving the stocks. Species Composition of Fish A change in species composition of fish in a reservoir is a result of species reacting differently to the alteration of living conditions after impoundment. Some species whose life cycles have been particu- larly disrupted may be unable to adapt to the new conditions and will disappear partially or even completely from the population, while many species can adapt to those changes in varying degrees and may continue to exist at changed abundance. The fluctuations may range from capability to maintain their populations at the same, more or less, levels com- paring with the pre-impoundment period, or certain species may increase their numbers as a result of environmental changes becoming favorable. There are several reasons for fewer fish species in a reservoir than in 118 former riverine conditions. They include: (1) reservoirs have fewer habitat types than rivers, particularly habitats associated with fast current; (2) a reduction of turbidities in reservoirs by means of sedi- mentation probably allows predators to reduce the population of small fish species more effectively than in the normally turbid rivers; and (3) an intensive fishery which accelerates the normal disappearance of rapidly growing valuable species, which are replaced by slow growing of undesirable fishes (Wajdowicz, 1964; Benson, 1968). Attention has been given to the effect of fisheries on possible changes of species composition in reservoirs after some years of existence. Rounsefell and Everhart (1953) stated that the intensive fishery exploitation of a water body effectively changed the relative numbers of different species. This occurs because practically all forms of fishing gear are more or less selective as to the species taken. Under certain circumstances a species that is especially vulnerable will decrease more rapidly than the others. Ostroumov (1957) reported that the fisheries had a remarkably negative effect on the formation of the fish population in the Uglich and Ivan'kovo reservoirs in the Soviet Union. He found intensive fishery exploita— tion in these reservoirs in the early years of their existences prevented an increase in numbers of bream and zanders. As a result, he recommended that it should be necessary for a cautious approach to fishery exploitation of newly created reservoirs. Commercial fishing should be permitted to a limited extent only after the formation of stocks of the most valuable fishes is completed. Any premature intensive fishery may disrupt the process of formation of the ichthyofauna, and lead to over—population of the new reservoirs with low-value fishes. 119 Population Distribution A knowledge of how fish are distributed in a reservoir provides valuable information in devising more efficient methods of sampling populations and more efficient methods of harvesting the fish crops. Most of the studies on the distribution of fish have dealt with fish collected by several methods such as trawls, gill nets, meter nets, electro-fishing, echo-sounder, and even poisoning. Fish are not distributed evenly throughout reservoirs. Studies on the TVA reservoirs indicated that the greatest abundance of fish in the mainstream reservoirs appeared midway between dam and headwaters where there are big expanses of shallow water from one to ten feet in depth (Gabrielson, 1950). Circumstantial evidence implicates several factors governing the distribution of fish in reservoirs. They are: (1) fish species; (2) stage in life history; (3) feeding habits; and (4) physico-chemical conditions of water. The distribution of fishes in reservoirs varies by species. Eley, Carter and Dorris (1967) investigated the distribution of fishes during summer in Keystone Reservoir, and they found drum were abundant in the upper reaches of the reservoir. White crappie were distributed generally throughout the reservoir from surface to 9 m deep. Black bullheads were abundant in the middle reaches in water above 24° C. Carp had a wide horizontal and vertical distribution pattern. Gars were more numerous in the upper reaches near the surface. Channel catfish were dominant in the upper reaches of the reservoir at the shallower depths during the fall and winter, but became distributed at all depths in the spring. In Canton Reservoir, distribution of walleye was different in various stages of its cycle (Grinstead, 1971). He reported that larval walleye moved from the spawning grounds at the dam site soon after 120 hatching and were pelagic throughout the reservoir until May. The young then concentrated in the shallow water near the shoreline, with the highest concentrations occurring within coves near the deeper areas of the reservoir. In August, they returned to open water, and concentrated near the bottom. During November and December, they moved to the deepest portion of the reservoir, where they remained throughout January and February. Netsch and Kersh et a1. (1971) reported that the abundance pattern of gizzard and threadfin shad in Beaver Reservoir reached a peak density 4 to 8 weeks after spawning began, with highest densities found in the upper reaches. Variation in distribution of fishes in reservoirs is closely related to feeding habits and their food availability. Summerfelt (1971) reported that the distribution of several species in Lake Carl.Blackwell, Oklahoma, was related to a habitat characterized by relatively shallow water with little organic matter. He found distribution of the flathead catfish, a highly piscivorous fish which feeds upon freshwater drum and gizzard shad, was directly correlated with the density of its forage. Distribution of white crappie was positively correlated to biomass of mayfly and gizzard shad. White bass were abundant in shallow littoral zones with abundance of mayflies. Freshwater drum was numerically correlated with abundance of oligochaetes and Chaoborus. There are several physico-chemical factors influencing the distri- bution of fishes in reservoirs. Coke (1968) reported that distribution of fishes in a bush-cleared area of Lake Kariba, Rhodesianambia, was markedly reduced with increasing depth of water. A similar phenomenon was reported by Halon (1972). With a large scale echo-sounding survey, he found the distribution of fishes was limited in the areas of shallow water close to shore and mainly to bays and coves. He stated that fishes 121 seem to concentrate in the evening along the shoreline and especially in the embayments, being distributed in remarkably high density from the surface to 15 m depth with maximum density at 6 to 7 m depth. Only at places shallower than 15 m was the evening concentration of fish distributed from the surface to the bottom. At dawn in the same places the major concentrations of fish had changed to a less dense distribu— tion extending further offshore to a distance of about 2 km. It appeared that in the areas around islands with steep shores, fish were found only in coves or in strips a few meters wide close to shore. Smith, Pugh, and Monan (1968) reported that the distribution Of juvenile salmonids in the Upper Mayfield Reservoir, Washington, was more concentrated in the areas adjacent to shore than in open waters. A reduction in reservoir volume may influence the distribution of fish as a result of increasing the relative thickness of the warm upper layer during high withdrawal periods in summer (Cady, 1945). He found the distribution of largemouth bass, which is the most important species of the Norris Reservoir game fish, was more abundant at 10 to 20 m deep than near the surface. Dendy (1945) marked temperature as the most significant factor in influencing fish distribution in Norris Reservoir. He stated that most Species of fish tended to move to deeper water as the summer progressed and as the isotherms moved downward. Horak and Tanner (1964) found rainbow trout, kokanee salmon, and white sucker of the Horsetooth Reservoir (1,890 acres), Colorado, moved into deeper waters during summer. Kokanee salmon were found most abundant in waters of 51-55° F, while rainbow trout and white sucker were concen- trated in 66-70° F waters. Changes in vertical distribution of fish between daytime and night- time are well known. It usually appears that fishes are aggregated 122 near the bottom in the daytime and dispersed over the whole volume at night. Netsch and his colleagues (1971) reported that the nighttime catch-rates Of meter nets and of midwater trawls on gizzard and threadfin shad in Beaver Reservoir were 5—110 times greater than daytime catch— rates. This may be a good example of how fish distribute in the reservoir between day and night. The concentration of dissolved oxygen in water is considered as the most significant chemical factor influencing fish distribution in reservoirs. Dendy (1945) reported that as oxygen depletion progressed beneath a density current in Norris Reservoir, fishes tended to move through the current to the warm, well-oxygenated water immediately above it. However, he pointed out that the presence of dissolved oxygen of 3 ppm or more in reservoir water did not appear to influence fish distribution. A similar phenomenon has been found in Keystone Reservoir (Eley, Carter, and Dorris, 1967). They reported that fishes tended to move through the chemocline to upper aerated water as soon as the oxygen content of the hypolimnion reached 2 ppm or less. Results from year-long observations with echo-sounders and gill nets in Bull Shoals Reservoir provided evidence that most fishes seldom occupy waters below the thermocline (Houser and Dunn, 1967). The nighttime distribution of fish was found to be remarkably uniform over the entire lake. There was a definite order of decreasing density with depth and the vertical distribution was sharply limited between the surface and thermocline during summer. Estimate of Fish Population RObson and Regier (1968) stated that monitoring of the numerical changes which occur in a population through the course of time is 123 essential to a basic understanding of pOpulation dynamics, production, yield and the rational management of a fishery. Several methods have been developed for estimating fish pOpulations, most of them attempting to estimate population size or relative abundance. Marking or tagging of fish and subsequent recapture is the principal field technique employed in the estimation of freshwater fish pOpulations. Another technique useful in measuring pOpulation density is the monitoring of the catch and fishing effort in an exploited pOpulation during a given period of time. A number of mathematical models, underlying the methods used in the estimation of size and other parameters of fish populations, are set. up with certain assumptions concerning either the population, the fishery or both in an attempt to make a reasonably close prediction of the changes in numbers, mass, and distribution of the populations. (1) Enumeration Methods The simplest methods of estimating pOpulation size depend directly on enumeration of a whole or a selected portion of the pOpulation. Draining of a pond, for example, may result in complete recovery of all fish present; fish migration through a narrow channel or fish ladder may yield complete enumeration. These methods can be used only in small water bodies or with migratory species. Whenever fish population estimates are required in large water bodies, it is necessary to employ other means. (a) The Area Density Method This method is a means of estimating populatiOn paralleling the total tally, by assuming that the population is nonmigratory at least. during the period of sampling, and areas of sampling are similar habitats. The sampling is executed by completely blocking an area (at 124 random) with nets and the total pOpulation in each section captured by poisoning (Henley, 1966; Hayne, Hall, and Nichols, 1967; Balon, 1972), electric shock (Klein, 1967; Vincent, 1971), or other means. The abundance of a pOpulation is estimated as the numbers or weights of fiSh per unit area of sampling and extrapolated to the whole body of water. (b) Acoustic Method This method estimates by means of the echo-sounder and sector scan sonar (Cushing, 1963). It is a useful study of a whole water column. But there are two very serious prOblems in that identification cannot be made directly and it is difficult to detect demersal fish in very deep water. However, the echo-sounder is common and very useful to commercial fisheries. It has been introduced to reservoir fishery investigation by several investigators; for example, Jenkins (1964), Houser and Dunn (1967), Balon (1972). Echo-sounder survey is a method of estimating the abundance of fish traces based on the presence or absence of fish within a given transmission. Abundance is estimated as the number of presences recorded per unit of distance traversed. (2) Mark and Recapture Methods Marking experiments can be used for determining the size of fish pOpulations in a variety of situations. This method has been used chiefly as a means for studying migrations, distribution, utilizing the return for growth studies, mortality, and population size. The ability to account for the presence and recovery of marked fish has come to be recognized as a powerful tool for studying population dynamics. Types of tags presently in use which show promise in reservoirs are the double-barbed (Spaghetti) dart, the vinyl tube spaghetti, the monel metal jaw, plastic streamer, and Swedish trailer (Jenkins, 1964). 125 Experiments have been employed in many reservoirs, such as in the TVA storage reservoirs (Manges, 1950), Searsville Lake, California (Wohlschlag, 1952), Stiles, Otis, and Sugden reservoirs, Massachusetts (Stroud, 1955), Bull Shoals Reservoir, Missouri (Hanson, 1962), Merle Collins Reservoir, California (Rawstron and Hashagen, 1972), and many others. Ricker (1958) recommended that in practice the methods of marking or tagging and recapture should be based on the following assumptions: (1) the marked fish suffer the same natural mortality as the unmarked; (2) the marked fish are as vulnerable to the fishing being carried on as are the unmarked ones; (3) the marked fish do not lose their marks; (4) the marked fish become randomly mixed with the unmarked, or the distribution of fishing effort (in subsequent sampling) is prOportional to the number of fish present in different parts of the water body; (5) all marks are recognized and reported on recovery; and (6) there is only a negligible amount of recruitment to the catchable population during the time the recoveries are being made. A review of methods used in estimating fish pOpulations by means of mark-recapture techniques is as follows: The Petersen Method This method was first introduced by C. G. J. Petersen in 1896 (Ricker, 1958) to compute rate of exploitation, and the total popula- tion of fish living in an enclosed body of water. The method consists of releasing a number of marked fish into a body of water on one occasion, and sampling for recaptures on a single occasion or over a single period of time. The estimation of total population is Obtained by equating the prOportion of marked fish observed in a sample to the proportion of marked in the population. Thus: 126 N a MC/R where M is a number of fish marked and released; C is the catch or sample taken for census; R is a number of marks found in the sample C; N is its estimate of total pOpulation. The variance of the sample is calculated by the equation: M2C C-R) R3 V(N) This method assumes that: (l) the marked fish become randomly distribue ted in the population before the second sample is taken; (2) the second sample is selected at random from the population; (3) the product of marked fish and catch for census must exceed 4 times the pOpulation size (Robson and Regier, 1968). The value of N although consistent is not the best estimate since the statistical distribution of R tends not to be normal. For this reason Bailey (1951) has prOposed the modified formula which gives an almost unbiased estimate as follows: N M(C+1) (R+l) with a sampling variance is: 2 M (C-R) V(N) (c+1)(c+2) During the same period Chapman (1951) has also recommended a modifica- tion Of the Petersen equation to decrease the bias of the estimate as follows: (Mi-1) (C+1) (R+l) 127 and a sampling variance is: 2 2 2 3 V(N) . N [(N /CM) +2(N/CM) +6(N/CM) ] Approximately the same time Schaefer (1951) has given the equation: (m1) (c+1) _ (R+l) 1 but he failed to give an equation for sampling variance. For any form of the Petersen estimate, the bias can be estimated by the following equation: -(m+1)(c+1) N Approximate bias = 100 e where e is the base of natural log. - 2.7832. The confidence interval of the estimate may be computed from the equation: C.I. - N + t .s where s and v are degree of freedoms equal to n - l and c - 1 respectively. The Schnabel Method This method is similar to the Petersen method except that marking as well as recapturing is done on a series of occasions. The funda- mental difference is that whereas in the Petersen method the prOportion of marked individuals (M/N) is assumed constant, in the Schnabel method, the population size (N) is assumed constant. A number of marked indi- viduals (M) is increased as the eXperiment proceeds. Miss Zoe Schnabel (1938) first studied the theory of this method and gave the following equation for estimating the population size (N): 128 N = XCt.Mt/ZRt where N is the population present throughout the experiment, Ct is the total sample taken on day t, Mt is a total marked fish at large at the start of tth day, Rt is a number of recaptures in the sample Ct- The principal assumptions of this method are: (l) the population is constant in size during the sampling, thus mortality and recruitment must be negligible; (2) all samples are taken randomly from the population. As was the case of the Petersen method, estimated ”R" tends not to be normally distributed at low levels. Here again a correction factor is applied to the original equation. Schumacher and Eschmeyer (1943) suggested that a better estimate would come from the equation: N a BC .(M )z/ZR .M t t t t and Chapman (1952) has recommended the equation: N = ZCt.Mt / ZRt + 1 From the last model, it appears that the value of +1 has much more effect when "Rt” is small. The confidence interval for the Schnabel type estimates can be calculated from the following equation: “ R 1/N - l/N t /——————— ¢,v 2 ( Ct'Mt) where t-value reads from Student's t-table at degree of freedom of (n-l), n is the number of samples included in the summations. I+ 129 (3) Determination from Catch Statistics This method utilizes the primary data on catch and on the effort eXpended in obtaining various segments of the catch. The fluctuations in catches usually reflect fluctuations in population numbers when the fishing intensity exceeds a certain level, and may be used as a reason- ably reliable index if taken at least from year to year (Nikolskii, 1969). He stated that variations in catch over shorter periods reflect short-term alterations in the annual cycle rather than fluctuations in. numbers. The principle of this method is only applicable when a pOpu- lation is fished until enough fish are removed to reduce significantly the catch per unit effort. The accuracy of forecasting depends on the ability to estimate the slope of the regression of catch per unit effort. Whenever a very small prOportion of the pOpulation is taken, the slope is either nil or slight. A change in slope makes a tremendous difference in the point at which the projection of the regression line cuts the X-axis. This type of estimation assumes that the population remains unchanged during the sampling period. Ricker (1958) has given the symbols for this method of estimation as follows: N0 is the original population size Nt is a pOpulation surviving at the start of time interval t Ct is the catch taken during time interval t Kt is a cumulative catch to the start Of time t C is a total catch (Ct) ft is the fishing effort during time t E: is a cumulative fishing effort up to the start of time t f is the total fishing effort (ft) Ct/ft is the catch per unit effort during time t. The actual procedures and corresponding computations can be made by two me ans 0 130 The Leslie and Davis Method This method was first introduced by Leslie and Davis (1939), with the assumption that "the population does not increase through recruit- ment and immigration, or decrease through natural mortality and emigra- tion during experimental period." The method involves plotting the catch per unit effort against cumulative catch over a period of time. A regression line is drawn by the method of Least Squares. As a result the catchability is indicated by its slope. Also, the X-axis intercept" is an estimate of the original pOpulation (No), and Y-axis intercept is the product of the original population. Ricker (1958) has given a formula for calculating the original pOpulation as follows: N Isa/b o where a is the Y-axis intercept and b is the lepe of the regression line. The variance of the regression line is: 2 Syx - 2y -bZ(XY)/n-2 The confidence limits can be calculated from the roots of the equation: 2 2 2 2 2 2 2 2 2 N (b -tp.S .C22) - 2N(-ba—tp.S ‘C12) + (a -tp.S 'Cll) = O or: 2 2 J/f 2 2 2 2 2 2 2 2 2 2 2 2 (b -tp.S .C22) where a is the Y-axis intercept, b is the slope of regression line, 82 is variance of the regression line, t is the t-value corresponding to a given probability P for n-2 degrees of freedom read from Student's t-table: 2 2 C11 - XX / nix (n-number of observations) C12 a 2X / an c22 = 1 / 2x2 131 The De Lury Method This method was deveIOped by De Lury (1947) to estimate number of fish at the beginning of a fishing season. It was applied with certain assumptions. They are: (1) the catchability of the fish remains constant during the sampling period; (2) the entire population is available to the fishery and natural mortality and recruitment are negligible; and (3) the units of fishing gear do not compete with each other, and if the number of units remains constant throughout the period of sampling, this provision can be ignored. The De Lury method is virtually the same as the Leslie and Davis method except this method involves plotting the logarithm of catch per unit effort (Ct/ft) on the Y-axis against cumula- tive effort (Et) on the X-axis. The fitted straight line yields the same statistics. Ricker (1958) has given a general equation for comput— ing the initial population for the De Lury method as follows: f N0 = C/(l - b ) where b is the antilogarithm of the SIOpe to Obtain the fractional survival of the stock after the action of one unit of effort; bf is the estimate of survival to the end of the eXperiment; and l - bf is the fraction of the stock removed. (4) Forecasting from the Catch Per Unit Effort The catch per unit effort is the catch by a set of fishing gear or by a vessel in unit time, the result being dependent on certain species of fish and on the fishing gear. It is usual to employ as the catch per net (gill nets), or the catch per trawling hour. This parameter is often taken as a basic assumption of fish pOpulation work that catch per unit effort is prOportional to abundance during the time fishing takes place. Thus, it can be used to evaluate the state of a population and to forecast relative abundance of fishes in reservoirs. Houser and Warn—“‘1: M 132 Dunn (1967) have demonstrated the estimation of relative abundance of the threadfin shad pOpulation in Bull Shoals Reservoir from data of midwater trawl catches by using the equation: 8 151 “1V1 / V0 The variance of population is calculated by the equation: Viui (111+ 6) l niei 2 /VO "M U) V(T) = i where T is a total number of fish in the reservoir and “i is a mean number of fish per standard haul in the ith strata. Thus: “1 “1 g jél xij / “1 V1 is the volume of water in the ith strata V0 is the mean volume of water contained in the standard haul 6 is determined strictly by characteristics of the midwater trawl at respective depths (d1) and not by the fish concen- tration at that depth. EXperiments were conducted in Bull Shoals Reservoir and Beaver Reservoir in July and September 1966 (Houser and Bryant, 1967) by using 8 feet square at the front opening and 45 feet in overall length mid- water trawl. The population estimation technique based on data of catch per unit effort in 8 ft vertical strata (Houser and Dunn, 1967). The results of total pOpulation estimates are shown in Table 6. They stated that even though the standard deviation appears large, the coefficient of variation is quite good considering the nature of the problem. The estimates from the trawl data for O-age threadfin shad were 1,790 fish, and a weight of 7.1 lbs per acre, and 3 fish, weight 0.1 lb per acre for older age-groups. The standing crOps of gizzard shad were 80 fish and 0.4 lbs per acre for O-age-group, and were 13 133 fish weighing 2.9 lbs per acre for older age-groups obtained from trawl data estimations. Table 6. Estimates of total pOpulations of threadfin (T) and gizzard (G) shad in Bull Shoals Reservoir and Beaver Reservoir in the summer 1966 (Houser and Bryant, 1967) Total 2 Coefficient pOpulation S S of Month Species (x 106) (x 1014) (x 106) variation Bull Shoals Reservoir July T 333.3 23.0224 47.99 0.144 C 0.94 3.1712 0.18 0.196 Sept. T 221.1 6.4395 25.38 0.115 Beaver Reservoir July T 289.8 22.2756 47.20 0.163 C 243.9 30.6356 55.35 0.227 Aug. T 201.5 43.7314 66.13 0.328 G 37.1 85.5142 93.01 0.251 Sept. T 42.46 1.2547 11.20 0.264 C 2.22 86.8040 93.17 0.420 Age Composition A knowledge of age and rate of growth of fish is extremely useful in fishery biology and fishery management. They are together the most important basic information for solving life history problems such as longevity, sexual maturity or spawning time, catchable size, environ- mental conditions of the water bodies, suitability for stocking, and continuing studies in fishery production. Several methods have been used in age and growth studies of fish. Rounsefell and Everhart (1953) listed the methods of age determination of the fish as follows: (1) comparison of length frequency distribution; 134 (2) marking or tagging and recapture; and (3) interpretation and count- ing of growth zones or annual marks which appear in the hard parts Of fishes. Among these, the simplest method is analysis of length frequency distributions. This method requires a unimodal size distribution of all fish of the same age (Tesch, 1968). It is easy to employ if there is no large overlap in the size of the individuals in adjacent age-groups, and is more generally useful in the younger age-groups of a pOpulation. However, it appears that the utility of this method declines with age for most teleost populations (Weatherly, 1972). Furthermore, it_is relatively useless in the trOpics where reproduction occurs several times per year. Marking or tagging method seems to be most satisfactory because it provides important data and explains several aspects of the mode of life of the fish, such as age, growth rate, migration, and distribution of fishes. Olsen (1954) stated that this method is almost the only‘ approach to age determination in certain fish such as the elasmobranchs, in which hard parts are unavailable and length frequency distributions are suspect. However, some problems still occur, since most tagging methods are not applicable to small fish or, if they are, they may cause great mortality so that recaptures are few. Many marked fish may lose their marks, and the marks often go unnoticed by the fisherman. The most frequently used method of age determination of fish is the examination of annual marks on scale, otolith, spine and finrays, Opercular bone, and vertebrae. The scale method is most popular for aging technique of fish (Creaser, 1926; van Oosten, 1929; Smith, 1954; Backiel, 1962; Chugunova, 1963; De Bont, 1967; Hile, 1970, Vukovic, 1970). May (1967) and Kim and ROberson (1968) determined age of cod and salmon from otoliths; Leonard and Sneed (1951) and Marzolf (1955) 135 studied age and rate of growth of the channel catfish from pectoral spines and vertebrae; Bardach (1955) used the Opercular bone as a tool for age and growth studies of the yellow perch; Boyko (1950) examined age of many fish species from finrays. The results Of determination were usually similar whether they used the same technique of study or not, and they also got a high degree of accuracy. The age composition of an eXploited fish pOpulation is normally determined by analyzing age composition of the catches taken at stated intervals over the season or year (Nikolsky, 1963). Recently, several methods have been recommended for determining the relation of age composition of a commercial stock (Gulin, 1968). They are: 1). Age composition of the stock may be determined by converting age composition of the catches over a season or year. This method assumes that: (a) the relative age composition of fish of individual age groups in the catch is the same prOportion to the relative age composition of the stock; and (b) the catch per unit effort is constant for all areas in the water body. Fishing is normally based on the densest concentrations of fish so that those conditions are not observed in inland waters. Thus, this method of estimating is impractical to determine a relative age composition of a stock in freshwater bodies. 2). Age composition may be obtained by methods entailing calcula- tion of the absolute numbers of the pOpulation from catches in a unit effort, size and age composition of the catches. Age composition of the commercial stocks is then estimated by extrapolating the samples of age analyses to total stocks. 3). Age composition of the stock may be calculated from the mean of samples taken to determine the age composition of catches with standard fishing gear. He noted most suitable fishing gear for this 136 purpose is an active fishing gear of the filtering type, whose design should be decided in relation to the conditions in the water and type of fish. It is evident that trawls are best suited for use as standard fishing gear for determining the age composition of stock in inland waters o Growth Study Growth is an important component of fish population dynamics because it is an important factor influencing the time of sexual matura- tion, reproduction, production, and fishing regulation. It appears that the growth process is specific for each species of fish. In natural waters, the growth of a fish population is dependent upon the abundance of the stock, food supply, space, temperature, growing season, and other environmental factors. The methods used in growth studies in fresh- water investigation fall into three main groups (Teach, 1968): (1). Direct observation. Growth may be studied eXperimentally by tracing the seasonal and annual increase of fish of known size and age in tanks, ponds, etc. (2). Tagging and marking. These methods require certain techniques which cause little or no retardation of growth such as the internal tags, coloring with dyes, and fin clipping. Study is then made by measur- ing the increment in length or weight of marked fish between liberation and recapture. Practically, this method is seldom used as a primary source of growth data because: (a) it is costly to apply on a large scale; (b) the growth data are usually obtained over relatively short intervals; and (c) growth of tagged fish may not be representative of the untagged pOpulation (Parrish, 1958). (3). Back-calculation of lengths or weights. This method is done by taking length measurements on skeletal structures and then 137 calculating the total length of fish at the end of successive years of life. Thus, its validity depends on the relationship between the growth in length or weight of fish and the growth of the skeletal structures over certain periods of time. The skeletal structure most used in this method is the scale, but otoliths and opercular bones also have been successfully used (Parrish, 1958). Much attention has been given to the nature of scale and body relationship. Tesch (1968) found when fish length was plotted on the Y-axis against scale radius on the X-axis, the relationship obtained may be either: (a) linear and passing through the origin (of the form: L=bS), or linear but not passing through the origin (of the form: L=a+bS); (b) curved with increasing slope; or (c) S-shaped with 310pe at first increasing, later decreasing. The back-calculation of growth history can be done by the following methods (Lagler, 1952; Nikolsky, 1963; Tesch, 1968; Hile, 1970). a. Lea Method. This method assumes that the length of the scale and that of the fish increase in direct proportion to each other. The relationship is linear with an intercept at the origin. Length of fish corresponding to any length of scale can then be calculated by the equation: S n Ln L.S where Ln is total length of fish at age n years, L is total length of fish at time scale sample was obtained, Sn is the distance between the annual ring and the focus at age n years, S is total scale. radius. b. Lee Method. This method assumes that the scale is not laid down at the birth of the fish, but somewhat later when the fish has A... .. l.... l ._= 138 already attained a certain length "a". The relation between fish length and a scale measurement is still linear but not directly prOportional to each other (of the form: L=a+bS). Rosa Lee therefore prOposed a new equation: S n Ln - S (L-a) + a where a is the size of the fish when scale first deve10ped. c. Monastyrsky Logarithmic Method. This method assumes that for many fishes the relationship between the growth of the scales and that of the body has a curvilinear character. The relation can sometimes be converted to a straight line by means of a transformation to a log- log relationship by the following equation: log L a K + n log 8 where K is intercept of the straight line on the ordinate (in log unit) and n is the lepe. In general, growth study usually compares the growth (length or weight) of the same Species from different basins or the growth of different species of the same age in their increments during the same life span (Chugunova, 1963). He also stated that it is impossible to use absolute increments for growth rate comparisons between different species or even of different sizes of the same species, but relative increment is acceptable. The parameters that give reasonable comparison include: (1). Chugunova Specific Growth Rate Method. It is calculated by the following equation: 139 log v2 - log v1 v O.4343.(t2-tl) where Cv is specific growth rate, v1 and v2 are the measured sizes, i.e., the length or weight at the beginning and the end of the time interval for which the specific growth rate is calculated, the number 0.4343 is a constant derived from change of base from natural to common logarithms, t1 and t2 express the time from the beginning and at the end of the interval for which the spe— cific growth rate is calculated. (2). Chugunova Growth Constant (Clt) Method. It is eXpressed by the formula: C = log 12 - log 11 . (t2 + t1) 1t 0.4343 (tz-tl) 2 where l is length of fish. Investigations have led to the discovery that the majority of fishes show two periods of growth, and some fishes show even three periods. Comparing these periods with the life span of the fish, it becomes clear that the first period coincides fairly closely with the time of sexual immaturity. The second period includes the time of sexual maturity, and the third period is the "period of old age." Thus, by using the growth constants it is possible to distinguish the period of growth for many species of fishes. But it does not characterize the intensity of growth and therefore does not permit the comparison of the intensity of growth by periods between fish of the same species taken from dif- ferent basins. (3). Chugunova Growth Characteristic. It is eXpressed as follows: log 12 - log 11 . 1 C 8 ch 0.4343(t2—t1) 1 The growth characteristics are applied to the comparison of the growth of a particular fish during different growth periods and also for the 140 growth of the same Species from different basins. Chugunova (1963) recommended that in comparison of the growth of fish of different species and genera the growth characteristic for the second period (after sexual maturation) be used, since this characteristic changes little within one species during this period even in different basins. In all the cases of evaluation of specific growth rates, growth constants, and growth characteristics, the average fish length at each age group is used and not the individual length. Reproduction (1). Rate of Maturation. Chugunova (1963) stated that the average number of individuals (expressed in percentages) spawning for the first time in any fish pOpulation is directly prOportional to the growth during their feeding period before reaching maturity. This statement appears to be true for the majority of fishes, but not for all and not in all cases. Sometimes, on the contrary, maturity occurs early with poor growth; for example, in crucian carp (in basins containing little food) and dwarf males of salmon. It is usually remarked that the age of maturing or rate of sexual maturity of a particular fish species depends on some external factors, the most important of which are: food, temperature, photOperiod and water currents. A great number of experiments have been carried out at the Kalarne Fishery Research Station in Sweden to study the connection between first sexual maturity, size (growth rate), and age in fishes (Alm, 1959). The results are summarized as follows: (a). Fish of a good growth rate reach maturity at a low age and then of a smaller average size than fish of medium growth rate which reach maturity at a higher age. Again, fish with poor growth become we: 7..--“ __ ' 141 mature at a higher age and their average size is smaller than of the fish matured at medium growth rate. (b). The age of maturity is usually higher in large-sized and often fast-growing fishes than in small-sized and slow-growing species. (c). The age of maturity in different pOpulations of the same species depends mainly on size and thus indirectly the growth rate. The maturity of fish with an initially good growth rate is reached at an earlier age than of the fish with a beginning poor growth rate. (d). The average size of the individuals in the year-class or, pOpulation with good growth rate is greater than in cases with poor growth rate. (e). Fish, on account of better growth rate, reach maturity at the lowest age and spawn a greater number of times than fish of a poorer growth rate and with later maturity. (f). The earlier or later age of maturity has not had any per- ceptible influence on mortality and longevity, and in spite of the fact- that the males practically always reach maturity one or two years before the females, mortality has not been perceptibly higher in the former than in the latter. The determination of rate of maturity needs further investigation. At this time only two methods are reported (Chugunova, 1963) to solve this problem. They are: (a) determination on the basis of spawning checks; and (b) over-all determination of the maturity of the sexual. products by dissecting the fish. He stated that the determination on the basis of spawning checks are sometimes difficult because spawning checks are not seen well on all fish and are often absent in some individuals of a given population. Therefore, techniques of determina- tion of spawning checks need further deveIOpment for a high degree of JA “a I..-“ -..__ - ' Y 'n.‘ ‘K 142 accuracy in interpretation when applied to the majority of fishes. (2). Fecundity. The fecundity of fish is defined as the number of ripening eggs found in the female just prior to spawning (Bagenal, 1967). Several parameters have been used in fecundity evaluation for fish, including individual fecundity, relative fecundity, and specific fecundity (Nikolskii, 1969). Individual fecundity refers to the number of eggs for the generation of that year present in the ovaries, or that should be laid that year. The relative fecundity is the number of eggs per unit body weight of fish. The specific fecundity is interpreted as the following relationship: SF - (l + r)l/pjs where r is the individual fecundity, p is the period between laying times, 1 is the age of onset of sexual maturity, and s is the ratio of the sexes. The fecundity of individual female fish shows significant varia- tions depending upon genetics, length, weight, age of fish, season, and food supply in the previous season (Le Cren, 1965). The number of eggs varies widely in different species of fish, ranging from a few large eggs in sharks to three thousand million in the sunfish, Mbla mold L., and fecundity of marine fishes is usually somewhat higher than in fresh- water or migratory fishes (Nikolsky, 1963). Typical results of fecundity investigation have shown that the number of eggs is approximately prOportional to the cube of the length, or linearly prOportional to weight or to age of the fish (Bagenal, 1968). It is evident that the number of eggs gradually increases with age in the majority of fishes, but as the individual approaches senility it usually begins to decrease (Nikolsky, 1963). He also pointed out that ii. 143 there is an increase in the numbers of eggs with the length of fish in all Species. Bagenal (1967) plotted fish length against fecundity and found their relation of the form: F-aLb. His further analysis using logarithmic transformation fit a Straight line by the method of least square, and fecundity can be estimated from the equation: log F - log a + b log L where F is fecundity, L is fish length, and a and b are constant. Furthermore, he found that if he plotted fecundity against weight of fish (without the weight of gonads) the result is a linear relation- ship of the form: F - a + bw where w is weight of fish without the weight of gonads. (3). Spawning. Nikolskii (1969) reported that the length of the spawning period and the mode of deposition of the eggs are very important features in pOpulation Studies. Prolonged or repeated spawning is an adaptation to unstable spawning conditions for a survival of the eggs. In many fishes the survival rate of the larvae is dependent on the time during the spawning interval when the eggs are laid. Le Cren (1965) stated that the number of eggs laid is influenced by several factors, the more important of which are: a number of spawning females, their age and size, the food supply in the period before spawning, access to spawning grounds, the area of suitable grounds available, and competi- tion for space on the Spawning grounds. (4). The Survival of Eggs and Fry. The survival rate of fish in the early stages of develOpment is variable; its fluctuations vary 144 greatly from one species to another. It is well known that the survival of the young is governed by the number and quality of the eggs and sperm, as well as the biotic and abiotic conditions. Nikolskii (1969) stated that variations are prominent in species with a very labile food supply, the nechanisms being substantially related to the supply of internal food received from the egg. Large fluctuations occur for species whose egg-fat content is low and whose fry cannot live long without an external food supply. It is evident that the amount and quality of the yolk are related to the feeding conditions of the parent pOpulation; thus they respond somewhat to the abundance of the offspring. Variability in external food supply after the larval stage usually causes reduced activity and growth together with increased losses due to predators, diseases and parasites. (5). Recruitment. The variation in recruitment depends on the number of parental stock, the number of eggs they lay, and the subse- quent survival of the young stages up to the recruit stage (Le Cren, 1958). In most fish pOpulations particularly those of species that lay a large number of eggs, survival in larval and young stages appears to decide the strength of the brood at the age of recruitment. The survival of a brood and its strength usually depend upon changes of climatic and hydrological conditions. If such factors can be identi- fied and measured there will be h0pe in making forecasts of some of the major fluctuations in recruitment and of making allowances for their effects when assessing pOpulation status. These problems need muCh more research into the whole aspect of the survival of larvae and young fish including the natural mechanisms controlling pOpulation numbers. 145 MANAGEMENT OF FISH POPULATION Practical management of fish populations in reservoirs depends on degree of environmental control that can be applied, on those factors that limit size of the pOpulation, and on the fishery purposes. Several of the following management measures have been devised to substantially increase production in the reservoirs. Selective Killing of Undesirable Species A selective kill has been accepted as an effective reservoir management technique for reduction of undesirable fish. The method consists of application of toxicants to the impoundments for either partial or total elimination of unwanted Species. Many toxicants have been used, but rotenone and its derivatives have been favored (Ryder, 1970). Conservational methods of commercial fishing have occasionally been adopted as the most feasible for controlling fish pOpulations in reservoirs (Thompson, 1955). (1). Rough Fish Control: A number of methods have been used, including chemical treatment for complete, partial, or selective control: netting, trapping, shocking, building barriers, altering the habitat, and using poisoned baits (Burns, 1966). A complete kill of rough fish in reservoirs is usually impossible; however, partial control may occasionally be desirable to facilitate establishment of a newly introduced game fish. A few selective toxicants have been tested but are not yet widely employed. For example, Pro-Noxfish was. applied at varying concentrations (0.15-0.30 ppm) over approximately dhree-fourths of the drawdown area of Lake Caterina (3,000 acres) near Hot Springs, Arkansas (Mathis and Hulsey, 1960). They found shad and drum were killed over the entire surface area, but they failed to give 146 quantitative estimate of numbers and weights of fish killed. They cited a more satisfactory estimate Obtained by the use of data from previous rotenone treatment in which 56% gizzard shad, 20% drum, and 22% game fish were killed in the total standing crOps of 221 lbs/acre. Commercial fishing has been used as a management tool to control competing rough fish in reservoirs. Many have been successful, but some may have limited value. To be effective, netting and seining must be intensive and must be continued to be directed at all sizes of undesirable species such as carp, river carpsucker, and freshwater drum (Jenkins, 1970b). EXperimental fishing in Norris Reservoir (Tarroll, Hall, and BishOp, 1963) in the winter of 1958-59 yielded 91,060 lbs of rough fish with indications of sufficient control of numbers of catfishes, carp, carpsucker, drum, and paddle fish. Commercial netting the following winter yielded only 39,517 lbs, even though the total netting effort was 1.4 times greater than in 1958-59. Similar results also occurred in the fall and winter of 1960, when 13,396 lbs were harvested with a greater daily netting effort. The catch per 1,000 yards net of dominant species (paddlefish, flathead catfish, carpsucker, carp) declined from approxi- mately 322 to 63 lbs. Jester (1971) reported that the smallmouth buffalo, Ictiobus bubalua, population in Elephant Butte Reservoir (37,500 acres) was reduced by 342,200 lbs in 6 years by commercial harvest. Biological control of reproduction as by introducing sterile rough fish has shown limited promise (Jenkins, 1970b). To date, the manipulation of water level during spawning season seems to be the most practical method. For example, a slight reduction in water level. during the Spawning season of squawfish, Ptychocheilus oreganensis, has been observed to cause heavy mortality of their eggs in Hayden Lake l’kfilfw if! 147 (Jeppson, 1957). Reduction of water level immediately following egg deposition of carp in Fort Randall Reservoir was an effective technique in reducing their reproduction (Shields, 1958). Stabilization of water level during spawning seasons in Elephant Butte Reservoir resulted in limiting pOpulation size of largemouth bass and crappie (Jester, 1971). (2). Forage Fish Control: P0pulation studies have indicated that gizzard shad, Dorosoma cepedianum, often comprise up to 50-80% of the standing crOp in reservoirs (Jenkins, 1961). A fast first-year growth of 150-175 mm in total length occurs in shallow and fertile reservoirs in the southern states, which renders them unavailable as forage for most predators by fall (Jenkins, 1970b). An overabundant pOpulation of adult shad then occurring, these fish will usurp nutrients and space in competition with other species and tend to suppress numbers and growth of economic fishes. Selective gizzard shad removal with rotenone concentrations vary- ing from 0.1-0.2 ppm has been accepted in southern states as a reservoir management technique (Zeller and Wyatt, 1967). They stated that rotenone at these concentrations will be toxic only to shad but generally non- toxic to game fishes. Carp, Cyprinus carpio, and freshwater drum, ApZodinotus grunniens, can be also affected with these concentration levels and some control has been reported for both species. The use of rotenone at these concentrations is also considered to have no effect on fish food organisms in these waters. Almquist (1959) reported that most phytoplankton, 200plankton, and benthos were killed at concentra- tions of 0.5-0.6 ppm. A similar result on benthos was reported by Lindgren (1960) with a treatment at a concentration of 0.5 ppm. The treatment with 0.5 ppm of 5% rotenone powder in Fern Lake, Washington, 148 resulted in a complete disappearance of zOOplankton in Open water, and it remained absent for over 3 months, while organisms along the shore edge disappeared for several weeks, and those inhabiting the dense aquatic weed partially disappeared (Kiser, Donaldson, and Olson, 1963). Carter (1957) reported his success in reduction of a gizzard shad pOpu- lation in Dewey Lake (1,100 acres), Kentucky, by selective poisoning with 0.10 ppm (0.3 lb/acre-foot) of 5% emulsifiable rotenone. He found the standing crOp of gizzard shad reduced from 102.0 lbs/acre in 1954 to 31.5 lbs/acre in 1955. After a selective kill, the percentage of the total weight of game fishes (bass, pike, crappie) increased in 1955 in both the netting and rotenone samples. Wyatt and Zeller (1962) treated the entire area of Lake Blackshear (8,515 acres) with emulsi- fiable 5% rotenone at a concentration of 0.13 ppm during a 6 hour period on September 21, 1965. They reported gizzard shad of all sizes were killed. The result indicated a successful selective kill for this Species, although a loss of 5-10% game fish was observed during the operation. Zeller and Wyatt (1967) recommended that the application of rotenone for selective gizzard shad kill should be used when the gizzard shad comprised at least 50% in total weight of standing crap. They stated that a period of 6 to 8 hours was generally accepted as the time needed for application of rotenone to reach lethal concentration for gizzard shad in order to avoid possible excessive kills of other species. Rotenone applications are recommended for every 3 to 5 years to maintain gizzard shad population at a reduced level, based on the assumption of a three-year life span for this species. Jenkins (1970b) reported the cost of rotenone treatment for selective kills was approximately $2 to $4 per acre. He also stated that the fishing success usually improves. immediately following gizzard shad kills, and reproductive success of 149 sport fishes increases in the next year. The beneficial effects last for one to four years. Other toxicants such as toxaphene and antimycin have been used to eliminate undesirable fishes in lakes and ponds. Toxaphene has several disadvantages when compared to rotenone. It is dangerous in concentrated form to other vertebrates; it has a long detoxification time several years in some cases; and it is more injurious to aquatic invertebrates (Northcote, 1970). An application of approximately 0.1 ppm toxaphene in Reservoir No. 4, Colorado, had a marked effect upon the macrosc0pic bottom organisms (Cushing and Olive, 1957). They found all larvae of the Tendipedidae were absent within three days after treatment. Recovery of the population in treated areas was complete in the ninth month after poisoning. Recently, Antimycin A has been recommended as a promising fish toxi- cant which Shows a degree of species selectivity (Lennon, 1966). Intensive trials in the laboratory and field have provided evidence that antimycin possesses qualities which distinguish it from other fish toxicants (Berger, 1965). He listed its principal advantages to include: it is lethal in parts per billion concentration to certain target Species of freshwater fish, including carp; its effect on most.species is irrevers- ible; it does not repel fish; it works well in cool and warm waters and in the presence of aquatic plants; it degrades rapidly; it has low mammalian toxicity; and it has little effect on phytoplankton, zooplank- ton, aquatic insects and amphibians. It has been reported that.gizzard Shad, trout, pike, carp, minnows, suckers, sticklebacks, whitebass, sunfishes, perch, freshwater drum, and sculpins are generally eliminated at 5-10 ppb of antimycin. Less sensitive species requiring up to 20 ppb were shortnose gar, bowfin, and channel catfish. Black and yellow 150 bullheads displayed the greatest resistance, requiring up to 120 ppb. Daphnia were killed at a concentration of 10 ppb in 24 hours at 54° F, while damsel fly larvae died at 100 ppb in 48 hours and bullfrog tad- poles were killed by 40 ppb in 24 hours at the same temperature. Antimycin is better suited to partial reclamation of lakes than any toxicant heretofore available (Lennon and Berger, 1970). It offers good Opportunity to practice selective control of target fish. They reported that the applications of antimycin ranging from 0.4 to 0.8 ppb in farm ponds of 1-9 acres, Georgia, were most successful in reducing overabundant mdnnows, sunfish, and crappie without significant harm.to largemouth bass. EXperiments in Harriet and Perch Lakes in northern Wisconsin with antimycin at 0.5 ppb killed all of the stunted perch without harm to northern pike, bluntnose minnows, bullheads, large- mouth bass and smallmouth bass. The cost of treatments based on the list price of $48.00 for an 8.25-pound can of Fintrol-S was only $0.64 per acre-foot at the 0.4 ppb concentration (Burress and Luhning, 1969). Compared with rotenone, it appeared that rotenone is more economical for total pond eradication projects but antimycin gives more reliable and favorable results for selective species removal and for partial treatment of ponds and small lakes. Smith (1972) reported that at under normal situations it would cost about 8 times more to use anti- mycin A than to use rotenone for a complete fish removal project (based on 1 ppm rotenone mixture and 20 ppb antimycin A requirement). For selective treatment based on 0.13 ppm rotenone mixture and 0.4 ppm antimycin A, it would cost approximately $2 to $4 per acre for rotenone (Jenkins, 1970b) and $0.64 per acre for antimycin A (Burress and Luhning, 1969). ? Elam-a: 13.1..me .lq 151 Stocking Fish stocking has proven to be one of the most successful tangible tools in reservoir management (Jenkins, 1961). In general, introduced species should not act adversely on economically or aesthetically valuable native stocks and environmental conditions. It should be fast growing, be able to breed in confinement, have its feeding habit related closely to the base of the food chain, or to food available in reservoirs, and be acceptable to man (Adesanya, 1969). The reasons for stocking or introducing new fish to reservoirs include: (1) to utilize ecological niches to which none of the existing species are adapted; (2) to increase fishing success by introducing species that are considered to be more desirable in the fisheries; (3) to restore. ”balanced pOpulation" by introducing substantial numbers of large preda— tors, or to replace year-class failures of important species; and (4) to provide a source of food for sport and commercial species. There is a great opportunity to obtain additional fish production by the introduction of fish species new to a particular body of water. Stocking of threadfin shad has been an amazing success in reservoirs of southern states. This species offers great promise as a forage fish due to its small maximum size, high fecundity, prolonged spawning, susceptibility to winter-kill, short life span, and ability to suppress r gizzard shad production (Jenkins,.l970b). Successful stocking in some reservoirs has been reported (Fetterolf, 1957). Satisfactory establish- ment has been found in.Watana Reservoir (6,430 acres), good reproduction, occurred in Woods Reservoir (4,000 acres), and in large reservoirs such as Norris Reservoir (34,200 acres), Douglas Reservoir (30,500 acres), and Dale Hollow Reservoir (27,700 acres) Wyatt and Zeller (1962) reported that the introduction of threadfin shad into Lake Blackshear 152 following gizzard shad kills has been a success. They found the thread- fin Shad made up to 67% by number of the total Shad population after the treatment in 1959. Successful stockings have been achieved for many game and commercial species such as trout, salmon, white bass, striped bass, walleye, northern pike, and muskelunge (Jenkins, 1970b). Rainbow, brown, brook, and lake trout have been introduced into various reservoirs. Rainbows yield. highest return. Most southern agencies prefer to stock rainbow trout I 200 to 300 mm long in late fall or winter. Periodic stocking of sub- L catchable (less than 150 mm) rainbows is necessary in most heavily fished coldwater reservoirs. Fingerlings (less than 100 mm) have been used successfully in new reservoirs where the native species have been eradicated from the area before impoundment, and in waters after com- plete pOpulation removal. Large numbers of kokanee salmon, Oncorhyn— chus nerka kennerlyi, fry were stocked in Lake Tahoe from 1949 through 1955. They became established but the pOpulation remained at_a low level until a dramatic increase in reproduction was observed in 1963 (Cordone, Nicola et al., 1971). Other introduced salmonids have been reported elsewhere with highly variable results, such as brook trout which fail to compete with other species in established reservoir popu— lations and brown trout which are less vulnerable to sport fishing. Introductions of whitebass, Mbrone chysops, were begun in.a Texas reservoir in the 1930's then spread throughout the southern states in the following decades. White bass are relatively fast growing, short- lived fish in reservoirs and are heavy consumers of gizzard shad and threadfin shad in open water, resulting in suppression of overabundant shad pOpulations. Striped bass, Roccus saxatilis, were introduced into reservoirs in the early 1950's. To date, resident Spawning 153 pOpulations are known to be established only in Kerr Reservoir (Virginia- North Carolina), Millerton Reservoir (California), and the lower Colorado River impoundments (Jenkins, 1970b). Walleye, Stizostedion vitreum, were introduced into reservoirs in hopes that they might prey upon shad, buffalo, carpsucker, and carp which are abundant in some reservoirs, such as in the Elephant Butte Reservoir in New Mexico (Jester, 1971). Stockings have been successful in many Shallow, sand and silt-bottomed reservoirs in Nebraska, Kansas, Oklahoma, ! and Texas. For instance, a reproducing pOpulation of walleye was established in Canton Reservoir (7,500 acres) through stockings in 1960-62 by the Oklahoma Department of Wildlife Conservation (Lewis, a 1970). Reproduction has been observed successful each year since 1964 with only the 1966-year—class considered weak (Grinstead, 1971). Northern pike, Esox Zucius, and muskellunge, ESox'masquinongy, are most important predators on rough and forage fishes in reservoirs (Jenkins, 1970b). Spectacular pike harvests have been reported in young impoundments in Wisconsin, Minnesota, North and South Dakota. Pike fry have been stocked in many reservoirs in southern states. In Beaver Reservoir, Arkansas, it has been observed that pike grew 5 lbs per year during the first three years of impoundment and reproduced at age one. Pike require extensive marshy sloughs or inundated terrestrial vegeta- tion along shoreline for a successful natural reproduction. In many cases, the natural reproduction of native fish is disrupted after impoundment and the various improvements do not bring about a large enough replacement of the stock. Some introduced species failed to establish pOpulations in the reservoirs. Attempts to solve these problems with stocking eggs and fry were not successful. The failures have led to the idea of a nursery pond built adjacent to the receiving 154 reservoir and connected by a manually operated gate and drainage canal system. For example, the Kakhovka Reservoir on the Dnieper River, USSR, has associated with it a large hatchery complex of 2,500 acres for pro- ducing 35 million yearling carp each year for stocking in this reservoir (Frey, 1967). The use of a nursery pond to raise fish fry to a more resistant stage, particularly in respect to predation before being released into the reservoirs, is highly successful in the reservoir fishery management. For instance, the native pOpulation of walleye in the North Fork River disappeared from Lake Norfork shortly after impoundment. Several years of stocking millions of walleye eggs and fry failed to establish a fishable pOpulation. Only 10 walleye were caught in this reservoir during the 13 year period, from 1950 to 1963 (Keith, 1970). Later he reported that using a nursery pond to raise walleye fry for 30 to 45 days before being stocked in the reservoir has been highly successful in establishing walleye fishery in.the Bull Shoals and Norfork reservoirs. Other successful nursery pond releases have been 4-6 inch striped bass, and 6-10 inch northern pike. The Tr». establishment of trout fishery in Lake Cumberland (50,250 acres) in g i Kentucky has been achieved by yearly stocking 6-9 inch rainbow trout during 1962-66 and of 6.6—10.l inch rainbows since 1967 (Axon, 1971). Stocking of desirable fishes in reservoirs has been deve10ped in r trOpical regions for the production of fish food rather than for recrea- tional purposes. Initial works have been reported by Hickling (1961) in the book Tropical Inland Fisheries. Favorable fish stocked in reservoirs are usually the vegetable and plankton feeders; quite a few are predators. The common carp, Puntius javanicus, Osteocheilus hasselti; Java tilapia, Tilapia mossambica, and kissing gouramy, Helostoma temminckii, have been successfully stocked in reservoirs in 155 Indonesia. The Indian carp, Labeo fimbriatus, was successfully stocked in Kanigiri-Duvvur Reservoir in Madras State, India. The Chinese carp, Cirrhinus mlitoreZZa; bighead carp, Aristichthys nobiZis; grass carp, Ctenophanyngodbn ideZZus, and striped carp, Probarbus juZZieni, have been stocked in Ubolratana Reservoir (102,500 acres) in northeast. Thailand. A dramatic growth was observed from the catch; the grass carp weighed 12.4 kgs in 2 year stocking, and the Chinese carp reached 7.4 kgs in one year, both species having been stocked as 16-20 cm fingerlings (Pholprasith and Waiwutto, 1971). However, they made no comment on the permanence of either species. Several species of Tilapia are making great progress in African impoundments. For example, an introduction of 5,500 fingerlings chiefly Tilapia pangani and Tilapia melanopleura, into Hombolo Reservoir (3,450 acres) in Tanganyika in early 1959 gave very satisfactory results in one year. Reports of success in stocking Tilapia app. in reservoirs are also mentioned in Rhodesia, Kenya, Uganda, and Ghana (Hickling, 1961). Increasing of Food Supply to Fish Higher production of fish in large lakes and reservoirs can be achieved by raising the supply of fish food. Fertilization of large reservoirs does not seem to be a practical approach because: (1) water exchange causes a loss of fertility with water discharges, and the resulting continued fertilization necessary; and (2) fertilization is too expensive (Irwin, 1956). A cheaper and better approach, improving the fertility of the littoral area, has been recommended (Kimsey, 1958). Recent studies indicate that the application of inorganic fertilizer for increasing fishing success and nutrients in localized cove areas of Norris Reservoir, Tennessee, was impractical (Wood and Sheddan, 1971). ‘flfifi?“’“”"-T!IIIV F P“: .‘__ 156 Although they found fertilization supported increased numbers of bottom organisms and zOOplankton, there was no significant change in numbers, size, species composition, or survival of fish. The introduction of various invertebrates into reservoirs in order to increase the food available to fish is extremely profitable. In the Soviet Union, introduced invertebrates include various cladoceran, amphipod, mysid, cumacean crustaceans, polychaetes and molluscs. Winberg and Bauer (1971) stated that, "During the last 15 years, intensive work has been done in the Soviet Union to enrich the fauna of large lakes and reservoirs through herbivorous invertebrate introduction." Good result has been achieved in the Kaunas Reservoir (8,000 ha.) on the Neman River. A successful introduction of 12 species of invertebrates into the Veselovsk Reservoir on the River Manich (tributary of the Don River) has been reported by Kruglova in 1962. Among successful species were the mysids, Paramysis kamaZewskyi. They are now found in all parts of the reservoir and their yearly biomass is about 5.7 gm/mz. In the Cymlansk Reservoir (270,000 ha.) on the Don River, the mysids, It kowaiewskyi, P. intermediag and the polychaetes, Hypania invalida and Hipaniola kowalevskyi, were introduced in 1954 with good results. In 1961 the mysids comprised one-third of its total benthos biomass (2 gm/mz). In North America the introduction of Mysis relicta and Pontoporeia affinis into large lakes as a source of fish food has been recommended since 1939 (Clemens, Rawson, and McHugh, 1939). A decade later, approximately 25,000 Mysis and Pontoporeia.were introduced into Kootenay Lake (154 sq.mi.) in British Columbia for the purpose of supplying large invertebrates as food for intermediate—sized rainbow trout (Sparrow, Larkin, and Rutherglen, 1964). Although Mysis took ‘5‘ A Fairer...- 157 approximately 10 years to become established in this lake, they still were successfully introduced, and now they are well established. Studies showed that they were utilized by rainbow trout (25-60 cm in length), Dolly Varden, Salvelinus maZma, kokanee, Oncorhynchus nerka kennerlyi, and mountain Whitefish, Prosopium’williamsoni. Their preliminary observations suggest that Mysis has increased growth rate of rainbow trout and kokanee. During 1963-64, 182,300 Mysis relicta were introduced to four reservoirs in California and Nevada (Linn and Frantz, 1965). The intro— duction into Lake Tahoe was primarily to provide food for juvenile lake trout, Salvelinus manaycush. The other (Lower Echo Lake, Hutington Lake, and Blue Lake) releases were made to increase the chances of establishing the Mysis locally, and to test their trout-forage potential in coldwater fluctuating reservoirs. Mysis is now established in Lake Tahoe, but its utilization by lake trout has not yet been measured (Frantz and Cordone, 1970). Three species of crustacea have been introduced into Swedish reservoirs as a source of fish food. They were Mysis relicta. Pallasea quadriSpinosa, and Gammaracanthus Zacustris (Fuerst, 1970). Approxi- mately 50% of impoundments were successfully pOpulated by these intro- duced invertebrates. It appeared that char, Salvelinus aZpinus; brown. trout, Salmo trutta; burbot, Lota Zota; and grayling, ThymaZZus thymaZZus, start feeding heavily on Mysis pOpulations. Elsewhere fish management attempts to increase production of large piscivorous species have been made by introducing forage fish. Threadfin shad have been stocked particularly into large reservoirs as an additional forage species to support the survival and growth of piscivorous game species (Swingle, 1970). Successful works have been reported; for 158 example, an accelerated growth of black and white bass, crappies, catfish, striped bass, and trout have been observed in reservoirs after threadfin shad introduction (Jenkins, 1970b). Kokanee, Oncorhynchus nerka kennerlyi, are frequently used as the major source of food for lake trout, Dolly Varden, and rainbow trout especially in certain waters in British Columbia, Washington, and Idaho (Seeley and McCommon, 1966). American smelt, Osmorus mordax, have been stocked successfully in Quabbin Reservoir, Massachusetts, to provide primary source of food for lake trout (Bridges and Hambly, 1971). They found the growth rate of lake trout increased and reached the minimum legal length of 18 inches at age 4, compared to age 5 prior to the smelt abundance. Regulation of Water—Level The manipulation of the water level in a reservoir has a profound effect on the production of fish and the composition of the biotic com? munity. Among several design and Operational factors which are sometimes adjustable are the extent and timing of the increase or decrease in water level and the size of minimum pool. Water-level fluctuations may pro- duce many effects on aquatic resources. They are: (l) stranding or trapping aquatic organisms; (2) destruction and lower production of rooted aquatic plants, benthic algae, and benthos; (3) affecting the success of spawning by uncovering nests or former spawning areas, or covering them to excessive depth; and (4) affecting migration of fish (D111 and Kestaven, 1960; Hunt and Jones, 1972). On the other hand, benefits to aquatic stocks may increase through fluctuation in water levels. For example, a reduction of levels immediately following egg depositions may permit the control of unwanted fish. Conversely, 159 flooding of reservoir margins during the Spawning season may aid the reproduction of desired species (Fraser, 1972). However, these effects are not only dependent upon degree of varia— tion in depth, but they depend more on time, area, and duration of flooding or lowering (Wood and Pfitzer, 1960). Decreasing of water level in summer of large Shallow reservoirs will destroy the conditions for the summer spawner and will reduce the area of feeding ground, whereas lowering of the levels in winter will result in mass mortality of young fish (Aronin and Mikheev, 1963). Quennerstedt (1958) reported that the divergences in water level conditions affect the zonal distri- bution of aquatic vegetation. He found the fluctuation of water level only 3 m in Lake Hotagen, northern Sweden, during the winter had caused a disappearance of the rooted vegetation and all vascular plants. The fall of water level not only inhibited the permanent growth of aquatic plants in the marginal areas, but it may also have exposed areas being used for spawning, killing eggs and fry (Jackson, 1966). Davis, Hughes and Schafer (1964) stated that the effectiveness of water level fluctua- tion on aquatic weed control was directly correlated to the Species present, and duration of fluctuation. They found an excellent control of Najas guadblupensis and Potamogeton spp. was achieved through the winter drawdown in Bussey Brake Reservoir, Louisiana, in 1962. The pool elevation fluctuations of Lake Francis Case precluded the establish- ment of a vigorous periphyton growth in this reservoir (Claflin, 1968). Aass (1960) reported that regulation of water level has some effect on fish food fauna in the Norwegian impoundments. He found Gammurus to exhibit poor adaptability to the lowering of the water level, particu- larly those that mainly inhibit shallow water. Fillion (1967) stated that the abundance and distribution of benthic fauna in Barrier Reservoir 160 in Alberta, Canada, were affected by water-level fluctuations. He found the maximum abundance of benthic fauna occurs only in the vicinity of the drawdown limits, and a marked reduction in density outside this region is evident. The effects of water-level fluctuations on the reproduction of fishes and the effectiveness of spawning in reservoirs are reported by several investigators. Runnstrom (1960) reported that up to 50 percent of the roe of the char in Lake Torron in Sweden.was destroyed.when the fluctuation reached 14 m in winter, because the major part of the roe came above the water and dried up. Yakovleva (1966) stated that the reproduction of the phytOphilic fishes in the Volgograd Reservoir, USSR, was inhibited as a result of the removal of water to irrigate the Volga delta during the spawning season. Il'ina and Gordeyev (1970) found a gradual reduction in the areas of the spawning grounds and of deterioration in the breeding condition of the phytophilous fishes such as bream and pike in Rybinsk Reservoir occurred in years when water-level was low and the marginal vegetation was not submerged. A similar phenomenon was also reported in the Kuybyshev Reservoir (Kuznetsov, 1971). He stated that the effectiveness of reproduction of the zope, Abramis baZZerus (L), is closely connected with the fluctua- tions of water-level regime in the spring. A relatively strong year- class was found only in years in which water-level was high during the spawning period in May. The fluctuations of water-level.in reservoirs are not always injurious; a deliberate drawdown is sometimes used as a management tool in reducing stocks of undesirable fishes. Otherwise, it may be used to establish favorable spawning and feeding areas for desired species in the impoundments by a practical application of managed fluctuations. 161 Hulsey (1957) reported that following fall and winter drawdown of the Nimrod Reservoir and subsequent filling caused a large increase of young largemouth bass, Micropterus salmoidSS, and whitebass, Mbrone chrysops, with a resultant decrease in a number of young channel cat- fish, IctaZums punctatus; carp, Cyprinus carpio; drum, Aplodinotus grunniens; and buffalo, Ictiobus 8p. Shields (1958) found the water drawdowns of 1-1/2 to 2 ft in Fort Randall Reservoir, South Dakota, p. following the peak of carp spawning in late spring showed an effective- E ness in limiting its production. Yakovleva (1969) stated that the fluctuations of water level at specific periods possibly improve condi- E h? tions and increase the breeding efficiency of the fishes. A reduction of water level in Volgograd Reservoir, USSR, by 1.5 to 2.0 m from normal. preserve level in summer led to improving the breeding conditions of fishes throughout the reservoir in the spring. Allen (1970) has sug- gested that the water-level in reservoirs must be maintained, or be’a little increased, during the spawning activity of desirable fishes. A level between reasonable limits is maintained for about two to three weeks or until the spawning is completed. This will avoid exposing the eggs to an extreme low level with a risk of stranding or submerging the eggs to too deep water. Management of Tail-Waters The effects of impoundment on downstreamnwater quality depends upon water retention period, impoundment depth, seasonal variation, character of reservoir bottom.(whether highly organic or inorganic), on the physical and chemical qualities of water entering the reservoir, wind action to provide circulation, and on the position and depth of water withdrawal from the reservoir (Sylvester, 1960). A large, long, 162 and deep reservoir with deepdwater penstocks appears to have many deleterious effects on discharged water quality. It will discharge water that is low in dissolved oxygen, high in carbon dioxide, and noxious gas such as hydrogen sulfide, resulting in downstream fish- kills. Water withdrawal from the hypolimnion will discharge water that is relatively warm in the winter and cool in the summer, which may or may not favor fish growth. A discharge of water from deep layers usually contains high concentrations of dissolved and suspended materials that may cause a loss of essential nutrients from the reser- voir, thus tending to deplete the productive capacity of the impoundment (Wright, 1967). Changes in volume of flow below the dam may produce several changes in aquatic stocks in different ways. They may increase or decrease feeding areas, available spawning grounds, and the productive capacity of the river below the dam (Dill and Kesteven, 1960). The variation in flow of hydroelectric projects may range from no flow to maximum. capacity for the generating facilities with maximum discharge peak occurring daily. A difference of water temperature downstream of 10 to 15° F may occur along with the water flow fluctuations particularly during the summer months. A severe problem is produced by a prolonged no flow period, causing the water to warm beyond the limits desirable for cold water fish (such as trout), or to expose areas of stream bottom which results in a decrease in its productivity. Therefore, considers: tion should be given to altering the Operation to minimize the prOblem. Pirozhnikov, Karpevich et a1. (1969) reported that a major technique for increasing the level of reproduction of semi-migratory fishes in the Volga-Caspian region is the supply of adequate water to the delta, which is necessary for the migration of the carp, bream, and roach for 163 spawning, feeding, and growth during the first weeks of their existence, and for the safe migration of the entire pOpulation of fingerlings to the principal delta channels and to the northern Caspian Sea. Even though the provision for regulating the dam resolved the problem of frequent wide variation in flows of the river downstream, there still are the problems of providing favorable water temperatures and dissolved oxygen content in discharged waters. It has been observed for many years that the temperature of water released from dams depends on the level of the outlets, particularly when reservoirs were thermally stratified. Middleton (1967) reported that the most practical solution to this problem is to design an intake structure or structures suitable for selecting water at the depth of desired temperature. Since outflows through the penstock intakes in a dam produce a ”withdrawal layer" as shown in Figure 10 (Brooks and Koh, 1969), management of water quality can be achieved either by managing through a single outlet or through mixed withdrawal according to the requirements. Figure 10. Selective withdrawal from reservoir through several penstock intakes at various levels in dam (From N. H. Brooks and R. C. Y. Koh, 1969). The dissolved oxygen content in discharged water is often lower than that normally present in the inflow and may closely approach zero at the point of discharge. Churchill (1958) reported that low rates of 164 discharges were re-aerated in relatively short distances downstream from the dam, whereas higher discharges required many miles of open—channel. flow before oxygen saturation was reached. Studies of the concentration of dissolved oxygen (D0) in water discharged from reservoirs indicated that during the summer, dams with deep intakes discharge water of very low DO content, dams with intermediate intakes discharge water of higher DO content, and dams with high-level intakes discharge water with higher D0 content (Knight, 1965). Therefore, it is possible to discharge water relatively high in D0 content by controlling the level from which water is selected for discharge. This can be done by the same means as temperature control as well as using a submerged weir and artificial aeration. Knight (1965) recommended the submerged weir as a tool for solving the problem. He claimed the submerged.weir was the most feasible means of improving D0 content of discharged water. His study regarded the construction of a submerged weir around the turbine intake of the Roanoke Rapid Reservoir as a solution to the problem of low DO discharge from low level intakes. This weir had two sides extending perpendicular to the face of the dam for a distance of about 275 ft, connected by an upstream side about 525 ft in length and extending upward to within 25 ft of the surface. It formed an underwater barrier to obstruct passage of deep water into the penstocks so that water was selected for discharge from levels above the crest of the weir and thereby acted as the equivalent of a high level intake. The weir even caused a significant improvement in average water quality. It may be- impractical for reservoirs with great depth because of high cost of its construction. A search for other practical methods of treatment has been a subject for continuing study. Wisniewski (1965) introduced the hydroturbine aeration method to resolve the problem. He reported that 165 the use of hydroturbine aeration at power dams has been successful for introducing air into the water in large—scale reoxygenation. This method appears to be low cost under most conditions. Recently, Speece (1970) has prOposed four alternative aeration schemes for improving of oxygen-deficient impoundment releases. They are: (l) in-place hypolimnion aeration of the stratified impoundment with commercial oxygen; (2) injection of commercial oxygen into the penstocks; (3) down-flow bubble contact aeration of discharge below dam with commercial oxygen; and (4) U-tube aeration of the discharges. The eXperiments for evaluating these methods have been performed on the Appaloosa Dam and the Low Mountain Sheep Dam. The results are summarized as follows: The in—place hypolimnion aeration is accomplished by injecting small bubbles of commercial oxygen deep in the hypolimnion to provide more time for rising bubbles to be completely absorbed. Pro- vision to inject commercial oxygen into the penstocks of a high dam in combination with in-place hypolimnion aeration can provide a "polishing" system for positive DO control in the discharge. The down-flow bubble contact aeration using commercial oxygen simultaneously provides for reasonably efficient oxygen absorption and striping of dissolved nitro- gen. lts use would be dictated by a need to lower dissolved nitrogen levels and produce saturated DO levels in the discharge. The U-tube aeration with air injection appears to be most advantageous for DO addition where a warmwwater fishery is involved. It can produce a completely saturated water easily and economically, even though it ini- tially contains low DO levels. Finally, he concluded that the aeration of oxygen-deficient impoundment releases for improving water quality appears to be feasible on a large scale without destratifying the reservoir. Thus the reserve of colder water in the hypolimnion is 166 kept intact for control of downstream temperatures. No sacrifice is made in water quality for downstream uses when provision is made completely to saturate it with DO before discharge downstream. Elimination of Fish Parasites and Diseases Parasites and diseases of fish may be one factor contributing to the fishery decline in lakes and reservoirs. They result directly in fish kills and affect the productivity of the stock through changes in growth rate and reproductive capacity of the individuals. A report of approximately 170,000 fish killed in the Deep Creek Lake, a 3,900 acre impoundment, Maryland, in the spring of 1954 resulted from Ichthyophthirius muZtifiZiis infection and Trichodina app. and with a fungus, Saprolegnia sp. (Elser, 1955). He indicated that the disease affected chiefly the yellow perch, Others including bluegill, pickerel and largemouth bass. The estimate of dead fish was about 7.5 times the total number of perch taken by anglers during 1951-53 period. Summer— felt and Warner (1970) reported that the protozoan parasite, PZistophora Ovariae, which develops in the ova of golden shiner, Notemigonus crysoleucas, causes damage to the ovaries, and destroys eggs. Infected eggs, if fertilized, may not commence deveIOpment, or death may occur in embryos, but it has not been known to cause mortality among adult fish. Hoffman and Bauer (1971) quoted a report of Reshetnikova, who described the effect of a parasite, Digramma interrupta, on the produc-. tivity of bream in the Cymlansk Reservoir, USSR. This parasite caused mortality of young fish, growth retardation, and sexual sterilization of adult fish. The losses were about 500 to 700 tons per year (12 to 14% of the total catch). The formation of parasitofauna of fish in reservoirs occurs as a consequence of the process of the formation of fish and other aquatic 167 organism pOpulations. It appears that parasites usually decreased during the first few years after impoundment. Izyumova (1964) commented that there was a certain decrease of the parasitofauna of fish during the first years of reservoir existence particularly parasites that were bound to intermediate hosts. He reasoned that this might be a result of host shortage in newly established reservoirs, because zoo- plankton, benthos, and other macro-invertebrates are still in the develOpmental phases. Becker and Evans (1967) reported that snails, amphipods, c0pepods, and ostracods which serve as intermediate hosts for many species of helminths evidently take a long period of time to f adjust to the new environment. Thus, the incidence of infection of the helminths in their definitive hosts occurs at a lower rate and. develOpment takes a longer period of time in newly created impoundments. Hoffman and Bauer (1971) stated that the decreased period is relatively short (about one year) for protozoa, Monogenia, and helminths using c0pepods as intermediate hosts, and is longer (three to five years) for trematodes using snails and vertebrates as intermediate hosts. Whenever the intermediate hosts become established, the amount of para- sites bound to these intermediate hosts increases. Therefore, it: firm—”- indicates that the process of formation of the parasite fauna of fish usually lags behind their intermediate host formations. For instance, r the formation of zooplankton and benthos populations in the Rybinsk Reservoir in the Soviet Union was completed during the first 6-8 years of its existence, whereas the parasite fauna still continued their develOpment in the following years (Izyumova, 1964). He indicated that changes of environmental conditions in a reservoir following the impoundment, such as slow current and higher temperature of impounded. water, have a tendency to favor the multiplication of parasites and 168 also for the invasion of fishes. Another example referring to the formation of parasitofauna in the large southern plain reservoirs in the USSR became stabilised in about 10 to 12 years after impoundment (Hoffman and Bauer, 1971). The fish parasites that succeed in a reservoir usually derive from various sources. They may stem from: (1) those fish parasites present in the rivers, streams, ponds and other water bodies which are inundated after impoundment; (2) those fish parasites which were added with introducing new fish Species to the reservoir; (3) those fish parasites which were transferred by other animals such as helminth eggs being distributed by fish—eating birds; and (4) those fish hJ parasites present in the watershed and being distributed into the I impoundment by means such as by surface run-off. As a result, the number of parasites in a reservoir tends to increase directly with age of the impoundment. The studies of parasites and diseases of fish contribute one of the most important steps towards increasing fish productivity of reservoirs. There are at least three important reasons to encourage studying fish parasites in reservoirs: (1) to recognize dangerous Species; (2) to determine which Species become more numerous along with other changes in the reservoir; and (3) to provide information for possible prevention and control of dangerous parasites (Hoffman and Bauer, 1971). They recommended that for obtaining precise data about the species composition and density of parasites in a given reservoir, extensive investigations should be made in both pre- and post-impoundment periods. Annual study is required for the first three or four years; thereafter, a biennial and triennial survey is necessary. It is also 169 important for best comparisons that samples should be taken at the same stations, season, and of the same size. In general, an abundance or outbreak of a given parasite is influenced by environmental factors either abiotic or biotic (Bauer, 1962). The abiotic factors include temperature, light, pressure of water column, oxygen content of water, hydrogen-ion concentration, and salinity. The biotic factors are based on the mutual relationship between the parasite and other living organisms. Among abiotic factors, temperature is considered most important. It determines not only the distribution of certain parasites and the character of its life cycle, but also affects the abundance. For example, the extent of trematodes, nematodes, cestodes, acanthocephalans, and parasitic copepods on fishes in Wikes Reservoir, Texas, was a result of thermal effluent drained into the reservoir which keeps temperature at or near Optimum conditions for their activity all year round (Smith, 1972). Other abiotic factors have more limited effects in freshwater reservoirs. Although the biotic factors undoubtedly play an important role in the ecology of fish parasites, unfortunately their roles have been so poorly studied it is difficult to evaluate their effects. Further experiments and observations are needed. The presence of fish parasites in reservoirs has been reported by many investigators. For instance, Iskov and Koval (1965) studied the parasite fauna of fish in both the upper and lower reaches of the Kakhovskoe Reservoir, USSR. They found the fish parasites in this reservoir comprised of 79 species, of which 41 species were common in both regions. However, they reported some protozoa (GZugea Zuciopercae), trematodes (Allocreadium spp., Matagonimus yokogawai, Neascus cuticola), and tapeworms (Silurotaenia siluri) were confined to the reservoir. ‘— 170 The most dangerous parasites are: GZugea Zuciqpercaa, CbtyZurus spp., Diplostomulum spp., Bothm’ocephalus gowkongensis, Ergaslus siebioldi, Tracheliastes macuZatus, LiguZa intestinalis, Digramma interrupta, and Henneguya cutanea Zongicauda. Devaraj and Ranganathan (1967) observed the incidence of Isoparorchis hypselobagri (Trematoda) among the cat— fishes (Wallago attu, CaZZichrous bimaculatus, Mystus aor) of the Bhavanisagar Reservoir, India. An early post-impoundment investigation of fish parasites of Volta Lake, Ghana, revealed that fishes were heavily infected with parasites. Those which were found were: Trichodina, Myxobolus, Thelohanellus, Henneguya, Dactylogyridae, Gyrodactylidae, Ergasilidae, Lamproglena, and Argulus (Paperna, 1968). About one—fifth (21.9%) of fish taken from Nungua Reservoir were parasitized with CZinostomum sp., Lernea sp., Ergasilus sp., and pentastomid larvae (Prah, 1969). Ergens (1966) investigated the effect of parasites on healthy-pike, Esox Zucius, in the Lipno Reservoir, Czechoslovakia. He indicated Triaenophorus nodulosus was the most dangerous parasite of the pike in this reservoir. It caused severe intestinal inflammation followed by inadequate digestion and retarda- tion of growth. Fortunately, it appeared to decrease in intensity of infection with age of the reservoir. On the contrary, the population of Ergasilus seiboldi appeared to be increasing and causing serious damage to all species of fish in this reservoir. In North America, there are only scattered published reports of epizootics in reservoirs, commonly serious problems caused by IchthyOph- thirius, Lernea, monogenetic trematodes, and Argulus (Hoffman and Bauer, 1971). A survey of fish parasites prior to construction of a few reser- voirs has been reported. Becker, Heard, and Holmes (1966) investigated a pre—impoundment burden of the helminth and copepod parasites of bass, ezzrrm 171 Micropterus spp., of the prOposed floodplain of Beaver Reservoir in northeast Arkansas. They found 21 species of helminths and c0pepods; 11 species of these parasites were recovered from hatchery fish used to stock the stream before impoundment. A complete analysis of the helminth and copepod parasites of the blackbass in Beaver Reservoir since impoundment was reported by Becker and Evans (1967). They examined 812 fish and found 9 species of trematodes, 3 Species of nematodes, 2 species of acanthocephalans, 1 species of leech, and 3 species of c0pepods. The monogenetic trematodes showed a general increase after impoundment, whereas the digenetic trematodes and all other parasites generally decreased. They also reported the parasitic copepod, Achtheres micmptem’, in the host, Microptems salmoides, seemed to adapt themselves from the river to the lake environment sooner than parasites with intermediate hosts in their life cycle. Spall and Summerfelt (1969) studied host-parasite relations of the endOparasitic helminths of the channel catfish and white crappie in an Oklahoma reservoir. They recovered 15 species of endOparasitic helminths (Digenia, Eucestoda, Nematoda, Acanthocephala) from 189 channel catfish and 207 white crappie. Statistical significance in. intensity and prevalence of certain helminths was found among different age classes of the hosts. The ontogenetic change in the food habits of channel catfish, from a diet of invertebrates to fish, was apparently the reason for changes in the occurrence of many enteric helminths. Changes relating to age in the crappie were limited to the occurrence of Posthodfiplostomum minimum where multiple generations of metacercariae accumulate in older fish. The feasibility of the control of parasites of fishes presents complicated problems in reservoir fishery management. Almost nothing 172 is known about the control of dangerous fish parasites:u11arge bodies of water. However, prevention and some means of controlling can be achieved in various circumstances. Hoffman and Bauer (1971) recommended that it is very useful to determine the fish parasites present in the watershed before the dam is constructed. If dangerous parasites are found and the water bodies are small, possible control may be done by fish eradication and chemical disinfection. In some cases, the control or eradication of parasites in an existing watershed would be economically impossible; the best solution seems to be the control of the parasites of fish introduced into the reservoir from hatchery ponds. This can be accomplished by checking hatchery fish for parasites before they are introduced into the reservoir and by controlling intermediate hosts in the hatchery ponds where it would be economically feasible (Becker, Heard, and Holmes, 1966). It appears that biological control methods have promise in control- ling parasitic diseases of fish in reservoirs. The methods are based on an accurate knowledge of the biology and ecology of both parasite and host. That is, its cycle of intermediate and definitive hosts, its life cycle, and the sensitivity of various develOpmental phases to external conditions must all be elucidated. The abundance of intermediate hosts in reservoirs may, apparently, be regulated by changing the types of aquatic animals in a given reservoir. It appears that an abundance of the intermediate inverte- brate hosts in a reservoir can be reduced by introducing aquatic animals feeding largely on these invertebrates. Bauer (1962) reported that the snail, Bithynia Zeachi, which is the intermediate host of the Siberian fluke, Opisthorchis felineua, in the ide, Leuciscus idhs, the dace, L. Zeuciscus, and the roach, Rutilus rutilus, in the Soviet Union's 173 reservoirs could be reduced by the introduction of the crucian carp, Carassius carassius, and ducks into the reservoirs to feed on them. In some cases, it might be possible to stock fish species which are not hosts of the parasites already present in the reservoirs. He gave the example that wild carp whould be introduced into reservoirs to replace the bream where their stocks suffer from ligulosis. This measure is believed to decrease the disease in bream. Some parasites that develOp in second intermediate or additional hosts can be decreased through the fishery management. This method calls for the reduction in numbers of fish heavily infected by a given parasite. In Canada, for example, in order to decrease the infection of whitefish, Coregonus cZqueaform's, and vandace, Coregonus aZbuZa, which were heavily infected by Triaenophorus crassus plerocercoids, were inten- sively caught in many lakes. The result after several years was a marked decrease in the intensity of whitefish infection. Intensive catch of pike, Esox Zucius, and burbot, Lota Zota, was recommended as an active means for controlling diphyllobothriasis in the Soviet Union's reservoirs. Since these two fishes are the main carriers of broad tapeworm plerocercoids, a decrease in their abundance in the reservoirs would therefore cause a decrease in the diphyllobothriasis. It is very interesting to know that some aquatic invertebrates and fish feed on fish parasites; thus, the introduction of these animals into reservoirs could limit parasite abundance. Minnows, Phoxinus 8pp., were used effectively to control mature Argulus and their larvae (Bauer, 1962). Hoffman and Bauer (1971) had reviewed several Russian publica- tions on this measure; for example, the ligulosis and digrammosis of carp in Cymlansk Reservoir could be controlled by extensively harvesting the young infected fish. The idea was practicable because the infected 174 young fish remained isolated from healthy ones and they gathered in coves and creeks of the reservoir. Furthermore, ligulosis can be controlled by increasing the pOpulation of pikeperch. This fish was found to intensively feed on infected fish, and such a method was successful in the SimberOpol Reservoir and the Karachunskoe Reservoir. Freshwater molluscs and oligochaetes also served as intermediate hosts for several fish parasites. It is possible to control these intermediate hosts by regulating the water level. Bauer (1962) stated that if the water level in reservoirs was rapidly decreased.when large numbers of snails were developing, most pulmonate molluscs would be stranded; then they could be raked away. If the level could be kept low for several days most of the snails would die. Devaraj and Ranganathan (1967) reported that the snails, Mblanoidbs scabra and M. tuberculata, serve as the intermediate hosts for the leoparorchis hypselobagri in the Bhavanisagar Reservoir, India. They recommended that the most feasible method to reduce the snails in this reservoir was by introducing a snail eating catfish, Pangasius pangasius, into the reservoir to feed on them. Furthermore, fish-eating birds also serve as definitive hosts for several fish parasites such as Ligula, Postodiplostomum, Hysteromorpha, and similar helminths (Bauer, 1962). These parasites become sexually mature and begin to produce eggs in the bird's intestine only a few days after the birds become infected. The eggs thus begin to be dispersed very soon after the birds arrive at a reservoir. Therefore, it is desirable to control them by any means before they can infect the invertebrates with a new generation of parasites. 175 FISHING REGULATIONS AND CONTROLS The purpose of fishing regulations and controls is to provide more fish for persistently high annual fish catches without destroying the stocks. Investigation has shown that this condition will succeed if the biomass increments (by recruitment and growth) are equaled by the biomass decrements (by natural mortality and fishing) over certain periods of time (Russell-Hunter, 1970). This statement can be demon- strated by E. S. Russell's equation: 82 - Sl + (A+G) - (M+C) where S1 and 82 are the total biomass of the eXploitable stock of fish at the beginning and end of time interval--usually a one-year period. A is the additional biomass gained by the young "recruits" which have grown up into the exploitable stock during the time interval, and G is the biomass added by the growth of individuals in both S and A of the l exploitable stock. C is the biomass of fish caught by the fishery during the period, and M is the biomass of fish lost to the exploitable stock by natural causes during the same period. In fact, an equilibrium in the stock occurs only where the stock can be maintained at the same size throughout the time intervals, thus: 81 - 82; and then, (Mi-C) = (A+G). However, a true state of equilibrium of an exploitable stock is rarely attained because of variations in fishing mortality rate. It is evident that fishing has a variety of effects on a pOpulation. Nikolskii (1969) stated that the variations in fishing intensity not only cause a reduc- tion of fish population, they also alter the growth rate, the population structure, and have an adverse effect on the normal reproductive capacity Io hr. Duo-Ills} .l l} 176 of the pOpulation. Therefore, it is necessary to have some means to control fishing for protection of valuable fish pOpulations. Winberg and Bauer (1971) pointed out that an important factor in creating high productivity of valuable fishes is the regulation of fish stocks by means of protective measures such as closed seasons, control of mesh size, and the types of gear allowed. In large water bodies, yearly limits for the catch of most valuable fishes are determined, based on scientific information of pOpulation abundance, growth, recruitment and mortality rates, relationship between catch from a u. ”as...“ {m l s stock to the amount of fishing and to the Sizes of fish at first capture (Dill and Pillay, 1968). Practically, the main measures for the control of fishing and protecting of valuable fishes in inland waters usually fall into three categories: (1) establishment of localities and times at which fish must not be taken; (2) establishment of the permitted sizes of fish that can be taken; and (3) establishment. of the prohibited types of fishing gear and the control of fishing activity (Beverton and Holt, 1957; Dill and Pillay, 1968; Tyurin, 1968; and Nikolskii, 1969). However, the suitability of these regula- tory measures has to be judged against economic and sociological condi- m:maq tions. They Should be established only when the need for them'has been determined and the effect of such measures estimated and found practicable. The closure of areas to fishing and establishment of closed seasons can effectively reduce fishing mortality and also help to control the sizes of fish caught. Fishing should be prohibited in the main Spawning grounds of valuable fishes and in the feeding grounds of the young.‘ Control of spawning areas and feeding sites of fry and immature fish is intended to allow Spawning and also the growth of the fry to the 177 Stage where they leave the areas. This is particularly important for lithOphilous and phytOphilous fish, since spawning may be disrupted and eggs and fry destroyed if fishing is allowed at the wrong time (Nikolskii, 1969). Regulation requires a specific period which is related to a knowledge of the spawning times and of the location of the fish on the spawning grounds and feeding areas. The correct decision on date of Operation is very important and may vary for each species and different areas. Furthermore, it often varies from year to year according to climatic conditions and ecological conditions of a water body. The establishment of minimum size is considered as an important control measure particularly for fishes whose reproductive capacity is low. Thus a limiting minimum size is not only determined to protect immature fish, but it should be large enough to protect first spawning fish. Nikolskii (1969) recommended that this Size limit must be determined from biological information on rate of increase_in weight, the maximum life-span, and natural mortality each year after maturity. Regulation of mesh size has been widely used for controlling the minimum commercial size in protected fish pOpulations because it does not affect the cost of fishing (Dill and Pillay, 1968). However, it is difficult to design apprOpriate mesh size regulations where the fishery bears on multi-species resources to ensure adequate protection for valuable fish and permit catch of low value species (Tyurin, 1968). In most instances these two requirements are contradictory because an increase in the mesh size of fishing gear needed to protect valuable fishes has the result of underfishing low value fishes particularly species of small size. Thus it has to be decided whether it is more harmful to remove some of the young of the protected fishes or to 18m- .-.-:~.a': . “1 "‘1 W15 178 contaminate the water with fishes of little and no value. Restrictions of fishing methods generally take the form of prohi- bition of or limits on the use of damaging methods, gear and implements, or prescriptional details such as mesh size (Dill and Pillay, 1968). Such restrictions are warranted when increased fishing effort will affect recruitment but should not result in the loss of efficiency and increased costs of Operation. Destructive methods of fishing such as the use of poisons and explosives must be prohibited as Should other methods of fishing whose harmfulness is generally recognized in inland waters such as twin trawls, coastal and deepdwater sweep nets, especially those with fine mesh (Tyurin, 1968). FISH PRODUCTION The production of fish in reservoirs is affected by morphological, physical, chemical, and biological factors. Rawson (1958), as reported by Jenkins (l967),listed the following factors as probable indices of reservoir productivity: area, mean depth, shoreline develOpment, storage ratio, water-level fluctuations, water temperature, average near bottom oxygen at mid-summer, water transparency, total dissolved solids, average standing crop of plankton and bottom fauna per unit area, average catch of fish in a standard gill net and a list of a few domi- nant plankters, bottom organisms and fish. Carlander (1955) found a significant increase in standing crOp per acre with increase in carbonate content of the water in midwestern reservoirs. Ryder (1965) found inverse relationship between fish production and mean depth highly significant. Jenkins (1967) studied the influence of some environmental factors on standing crOp and harvest of fish in 210 reservoirs of the United States by using Regression Analysis. On single variable analyses, he found the variables with the greatest influence on total Standing crop were dissolved solids, area, and shore develOpment (positive effects). Shad crops were positively influenced by increases in age and dissolved solids and decrease in storage ratio. Sport harvest was negatively related to age and area. Commercial harvest was positively related to age, but negatively to mean depth and storage ratio (Table 7). In further studies using multiple regression analyses he found the 179 180 Table 7. The relationship between single environmental factors and standing crOp and harvest in 127 U. S. reservoirs (two symbols indicate positive or negative correlation at 95% confidence level; three symbols at 99% level) Dependent variable (poundjacre) Total Clupeid standing standing Sport Commercial Independent variables crop crOp harvest harvest Number of reservoir 127 116 121 46 Surface area in acres +++ --- Mean depth (feet) --- Storage ratio -- -- Shore development ++ Dissolved solids (ppm) +++ +++ Age of reservoir (years) +++ --- '+++ From R. M. Jenkins, 1967 interrelationships between these six environmental factors and standing crops and harvests: 1). With increase in total dissolved solids, an increase in stand— ing crOp and sport fish yield; E“ 2). With increased age of reservoir, an increase in clupeid crOp and commercial harvest, but a decrease in sport harvest and little effect. I on total standing crOp; 3). With increased storage ratio (i.e., lower water exchange rate), a decrease in standing crOp and commercial harvest and an increase in Sport harvest; 4). With increase in reservoir area, a decrease in Sport harvest; 5). With increase in mean depth, decreases in total standing crOp and sport and commercial harvests; 181 6). With increased shore develOpment, increases in total standing crOp and sport harvest, but a decrease in commercial harvest. The effects of engineering design and Operation together with selected reservoir environmental variables on fish standing crOp have been investigated in 140 large reservoirs (Jenkins, 1970a). Data‘were interpreted by logarithmic partial correlation and multiple regression analyses. He found logarithmic partial correlation revealed highly Significant (0.01 confidence level) positive effects of outlet depth, shore develOpment and dissolved solids on total standing crOp in.total samples. At the 0.20 confidence level, the crOp of all sport fishes was positively influenced by outlet depth, storage ratio and shore development, but negatively by mean depth. In 54 hydrOpower reservoirs with a stable thermocline, positive effects of increased storage ratio and dissolved solids on total crOp were evident at the 0.05 confidence level. Increase in thermocline depth had a negative effect. In 25 hydrOpower reservoirs without a stable thermocline, clupeid (shad) crop was negatively correlated with surface area, mean depth and water level fluctuations (Table 8). Recently, Brylinsky and Mann (1973) reported that the interpreta- tion of data collected from 43 lakes and 12 reservoirs, distributed from the tropic to the arctic as part of the International Biological Program (IBP), showed variable solar energy input was a greater influence on production than variables related to nutrient concentration in the water. Le Cren (1972) found high correlation between primary production and fish production in experimental ponds. Jackson (1966) observed greater Sport harvest in trOpical reservoirs than in reservoirs of temperate regions. He compared average annual sport harvest of 36 pounds per acre in TVA reservoirs to 40-50 pounds per acre in Lake Kariba, Africa. "pm" It L‘”fl_‘£ 182 Table 8. Logarithmic partial correlation of environmental variables with total fish standing crOp of 140 reservoirs (44 hydro- power mainstream, 37 hydropower storage, and 59 non- hydrOpower reservoirs) (one symbol indicates positive or negative correlation at the 0.20 confidence level; two symbols indicate at 0.05 level; hree symbols at 0.01 level) Total fish standingfcroP None Environmental Total Hydropower reservoir hydropower variables samples Mainstream Storage reservoir Surface area Mean depth - -- Outlet depth +++ - -++ Water level fluctuations - Storage ratio + Shore develOpment +++ ++ ++ Dissolved solids +++ +++ +++ +. Growing season ++ + Age of reservoir + From R. M. Jenkins, 1970a COOper (1966) pointed out that high production of fish in new impoundments is a results of water enriched with nutrients from newly flooded sub- strates which favor production of plankton. This condition consequently results in good survival of fish fry and young, and good growth rate of fish. Many investigations have indicated that the growth of zooplankton in reservoirs and the level of their biomass greatly exceeds the growth of zooplankton in former rivers. Thus, plankton feeders as well as young fish of other species are well supplied with food at the stage of‘ plankton nutrition (Loffe, 1972). In evaluating the bioproductional effect of river impoundment, Pirozhnikov (1972) reported that favorable effects of impoundment revealed an increase in number and total biomass of plankton and benthos. Such increments led to relatively high fish productivity of new reservoirs (Figure 11). 183 50 . ,0 E 45 4 .'° ‘E 0...... °: :0 0'. 4o — .. " . benthos feeding fish 35 -* S. 4 E ,ffl; 3o _. :' ’3' *2. : f 3 “E o H. k" 2 . ; g"\-predatory fish 5 "‘ o. 7‘ k .- r o «—E 0 ‘fl - v- 20 ‘ 15 — 10 - 5 'd plankton feeding fish 0 I l 1 T F 1 l l l T 6 8 10 12 14 16 Years of impoundment Figure 11. Annual catches of plankton feeding, benthos feeding, and predatory fishes in Tsimliansk Reservoir, USSR. (From P. L. Pirozhnikov, 1972) It is evident that most reservoirs have greatly increased fish production over river conditions. Fitz (1968) investigated the changes of standing crOp of the Clinch River before and after impoundment by the Melton Hill Dam. He reported that pre-impoundment netting yielded 1,463 fish weighing 1,987 pounds. Rough fish dominated the catch; the game fish prOportion was only 5% by number.and 2.6% by weight. After impoundment rough fish continued to dominate gill-net catches, but the proportion of game fish increased to 14% by number and 11% by weight. Average catch of game fish per net—day also increased. Runnstrom (1953) investigated the changes in fish production of impounded lake (Torron) in northern Sweden following up-regulation in 1937. He found ‘F: 184 the catch of fish in weight showed a rising tendency during the first few years. The yield for 1940 was almost double the catches before impoundment. Then yield declined during the years 1941-44 and with various degrees of fluctuations in the following years (Figure 12). 200 a 160 _ 120 _ 80 — 40 - 0 f 1 I I T I T T T I T 1936 38 4o 42 44 46 48 ' 1950 year Figure 12. Relative annual catch of spawning char in.weight during the period 1937-1950. (From S. Runnstrom, 1953) Carter (1969) investigated the Barren River during a three year period preceding impoundment and in Barren Reservoir during the first three years of impoundment to evaluate changes in fish composition and biomass. He found the fish population of the inundated section of Barren River increased in number from an average of 522 fish per acre before impoundment to 5,705 fish per acre for the first year of impound- ment. Fish biomass increased from an average of 111 pounds per acre before impoundment to 194 pounds per acre the first year of impound- ment. The second and third years of impoundment the biomass averaged 201 and 241 pounds per acre respectively. The estimated annual harvest 185 increased from an average of 13,507 pounds before impoundment to 38,719 pounds (4.0 lbs/acre) in 1965. In 1966, the total harvest was.estimated at 30,656 pounds (3.6 lbs/acre). Turner (1971) Stated the total sport. harvest is much greater in the reservoir than in the river. He estimated the sport catch from Rough River, Kentucky, before impoundment was 904 pounds. After impoundment the catches were estimated at 29,623 pounds in 1961; 79,540 pounds in 1962; 60,756 pounds in 1963; and 48,320 pounds in 1964. The average Sport harvest increased from 3.5 pounds to approxi- mately 15 pounds per acre (Table 9). Table 9. Estimated weight of sport harvest in pounds per acre of surface water from Rough River before and after impoundment Sport Rough River Rough River Reservoir harvest 1959 1961 1962 1963 1964 Weight 3.50 5.80 15.50 15.10 9.40 (lbs/acre) Carlander (1955) stated that the average standing crop in mid- western reservoirs was almost 400 pounds per acre; in other reservoirs and ponds, 200-300 pounds per acre, compared to 125-150 pounds per acre in warmdwater lakes, and less than 50 pounds per acre in trout lakes. These figures are well above the actual harvest in most.reservoirs. Investigations based on records collected from thirty-one states showed that the average sport harvest from large reservoirs in 1960 was approxi- mately 15.7 pounds per acre at warmdwater reservoirs and 9.0 pounds per acre at cold—water reservoirs (Stroud, 1966). On the analyses of data 186 collected from 127 reservoirs throughout the United States, Jenkins (1967) reported that in Spite of a mean standing crop in these reser- voirs of 186 pounds per acre, the mean sport fish harvest (121 reservoirs) was only 22.6 pounds per acre, and mean commercial harvest (46 reservoirs) was 10.2 pounds per acre. Benson (1968) also reported that the commer- cial fish harvests in Missouri mainstem reservoirs were low (Table 10), resulting in under-exploitation of fish populations in these impoundments. Table 10. Commercial fish catch from Missouri River mainstem reservoirs in 1963 Missouri River mainstem reservoirs Variable Fort Peck Garrison Oahe Francis Case Surface area 233,000 360,000 358,000 104,000 Commercial catch (lbs) 268,400 52,600 29,700 379,900 Average pounds/acre 1.15 0.15 0.08 3.65 However, intensive harvest has been reported from the southeastern reservoirs (Parson, 1958). He found the average fish catch from 6 main- stem reservoirs was 354 pounds per acre, and 146 pounds per acre for 9 storage reservoirs. Frey (1967) reported annual commercial catch in reservoirs of the Soviet Union ranged from 18 to 36 pounds per acre. It is apparent that fish production in reservoirs fluctuates variously following a typical pattern of high initial productivity, a sharp decrease and then a gradual rise to somewhat near half the magnitude of the initial phase. A six year record on sport fish harvest in Clearwater 187 Lake, a Missouri reservoir, during 1949 to 1954 showed 6.8 lbs/acre in 1949; 10.4 lbs/acre in 1950; 31.4 lbs/acre in 1951; 15.2 lbs/acre in 1952; 25.7 lbs/acre in 1953; and 22.1 lbs/acre in 1954 (Patriarche and Campbell, 1957). Gasaway (1970) reported the annual commercial fish harvest in Lake Francis Case (impounded in 1952) fluctuated from a maximum yield at 579,735 pounds in 1960 to 129,741 pounds in 1968 (Table 11), comparing with annual commercial catches in Rybinsk Reservoir in the Soviet Union as reported by Ill'na and Gordeyev (1970) of 9,488,158 pounds in 1954, 9,031,160 pounds in 1958, and 6,061,389 pounds in 1967, respectively. Total catches in Volgograd Reservoir were 6,440,298 pounds in 1963; 5,955,066 pounds in 1964; 4,543,681 pounds in 1965; and 5,555,592 pounds in 1966 (Yakovleva, 1969). The numbers of food fishes and the total fish mass in Kremenchug Reservoir have increased from year to year since 1960 mainly in connec- tion with increase in plankton and benthos (Pirozhnikov, 1968). The catches increased from 1,578,273 pounds in 1960, 3,073,390 ounds in 1961, 5,593,952 pounds in 1962, 8,928,850 pounds in 1963, to 12,176,888 pounds in 1964. In Poland, Wajdowicz (1964) reported commercial catches in Goczalkowice Reservoir (completed in 1955) were 43,559 pounds in 1958, 65,311 pounds in 1959, and 58,221 pounds in 1960. Produc- tion per acre was 6.70 pounds in 1958, 11.16 pounds in 1959, and 9.82 pounds in 1960. Harding (1966) reported fish production in Lake Kariba, Zambia, following the completion of the dam in 1958 were 23,036 tons in 1959; 21,316 tons in 1960; 22,578 tons in 1961; 23,944 tons in 1962; and 31,483 tons in 1963. In India, Sreenivasan (1967) reported the catches in Stanley Reservoir were 403,739 kgs in 1960-61; 347,645 kgs in 1961-62; 443,450 kgs in 1962-63; 407,901 kgs in 1963-64; and 222,647 kgs in 1964-65. The average catch per hectare was 55-60 kilograms. 188 Aomma .mmzmmmo .m .0 mo emuu0dou muse aoum emumaooamuv ouom\mocsoe os.a am.m Na.m em.m oo.m am.e ma.m Ho.e mN.o ma.~ as coumo Amnav an.ama woe.mmm mo~.sqm kma.amm mom.oem amo.wos aoa.amm Hak.~km mme.aam moa.ama zooms Hence mesa Nome some some «can mess mesa some case amaa assay use» mess on amaa .mmmo magnate mass as omm>ome Hmaoumaaoo .HH «Home 189 Many attempts have been made to estimate the fish production potential of reservoirs on the basis of physical and chemical factors. These attempts were also based on data of sport catch and commercial harvest from the impoundments. It appears that production has corre- lation with the physical and chemical factors (both positive and negative) as well as on length of the food chain. Hayes and Anthony (1964) demonstrated that there are significant positive relationships between production and the three factors of area, depth, and alkalinity. From their studies on productive capacity of North American lakes, they gave a formula to predict Productivity Index (PI) for any lakes using acres and feet. The formula is: log PI. = 0.031 + 7.31.10'5xl - 0.517x2 + 0.287x3 where Xl - u/lO8 / area in acre; X2 = log depth in feet; and X3 = log methyl orange alkalinity in ppm. By using this equation they calculated the theoretical Productivity Index of Clearwater Lake, a Missouri reservoir, as 1.45. They predicted an annual Sport catch from this reservoir of 26.4 lbs/acre, and a commercial catch of 6.1 lbs/acre. Ryder (1965) estimated fish production of north temperate lakes by using the regression of yield on mean depth and total dissolved solids. He related fish production in pounds per acre per year with a Morpho- edaphic Index (M.I. - T/D; where T a dissolved solids in ppm and D a mean depth in feet). When plotted logs of fish production against logs of morphoedaphic indexes they obtained a straight line relationship. By using this procedure, Benson (1968) estimated the potential fish pro- duction in the Missouri River mainstem reservoirs. He found the poten- tial fish yield ranged from 2.5 pounds per acre at Fort Peck to 6.3 pounds per acre in Lewis and Clark Lake. He commented that "it is 190 probable that these reservoirs, with their continual water renewal, could exceed the above yield figures." In a recent paper, Jenkins (1967) has deve10ped models describing the influence of some important environmental factors on reservoir fish standing crOp and harvest. He listed those of greatest apparent utility as: (a) curvilinear regression of standing crOp on morphoedaphic index; (b) multiple regression of standing crop on dissolved solids, shore develOpment and storage ration; (c) regression of Sport harvest on dissolved solids, growing season, age, area, and shore develOpment; and (d) commercial harvest on growing season, mean depth, storage ratio, age, and water level fluctuations. He gave an equation for calculating reservoir standing crOp on morphoedaphic index as follows: Y = 2.07 + 0.164 X where Y equals log (standing crOp), and X equals log (morphoedaphic index). The coefficient of correlation (r) is 0.325, significant at. the 0.01 level. Regression of sport harvest in 121 reservoirs on, morphoedeaphic index was Y = 0.88 + 0.183 X; r = 0.23; significant at the 0.02 level. Commercial harvest versus the index in 46 reserw voirs was expressed by Y = 0.52 + 0.210X; r = 0.21; not Significant at 0.05 level. In his multiple regression analyses, a series of regressions between total standing crop, clupeid standing crOp, sport and commer- cial harvest, area, mean depth, storage ratio, Shore develOpment, dissolved solids, and age of reservoir was computed and tested for Significance. Single equations were selected to relate clupeid standing crop, and sport and commercial harvests, to the most influential environ— mental factors (Table 12). In 1971 Jenkins and Morais reported their 191 Table 12. Multiple regression equations relating clupeid standing crOp, sport and commercial harvests to various combinations of physico-chemical factors which were selected by a step-down procedure as being most highly significant and with a rela- tively high R2 value (all data except area are logarithmic eXpressions) Constant Prob. for Regres- Standard of a Dependent simplified Independent sion coef— Reg. Mult. larger variables model variables ficient coef. R2X100 R2 Clupeid 0.828 Diss. solids 0.276 0.240 16 7.2x10-4 Standing Age 0.247 0.221 crOp Storage ratio -0.154 -0.192 (N-102) Sport 0.129 Age -0.318 -0.270 20 3 0x10.”4 harvest Diss. solids 0.305 0.245 (N=99) Area 0.001 0.284 Shore devel. 0 378 0.251 Commercial 0.734 Mean depth -0.612 -0.369 37 4.8x10-l+ harvest Storage ratio -0.174 -0.230 (N-4l) Age 0.572 0.123 (From R. M. Jenkins, 1967) studies on the influence of environmental variables in relation to reser- voir sport harvest. They derived the formula: log Y - 0.2775 - 0.2401X + 1.0201X - 0.2756X l 2 3 where Y is log total harvest in kilograms per hectare, X1 is log area, X2 is log growing season, and X3 is log age of impoundment. By using this formula they predicted the harvest for Beaver Reservoir, Arkansas, through the first 6 years of impoundment as 208 kg/ha (186 lbs/acre) compared to field estimated total yield for that period of 176 kg/ha 192 (157 lbs/acre). For Bull Shoals Reservoir, the predicted harvest from the second through sixth year was 136 kg/ha (121 lbs/acre) compared to field estimated total yield of 145 kg/ha (129 lbs/acre). It appeared that most reservoirs Show tremendous increase in fish production over river conditions. Typically, a maximum production is reached in the first few years after the impoundment, then follows a rapid decline to somewhere near half of its initial maximum level. Thereafter, it fluctuates in various degrees, mainly depending on environmental conditions of the reservoirs. Evidences of this were found in reservoirs of many countries throughout the world such as in the United States, Soviet Union, Sweden, Poland, Zambia, and India. Fish production in reservoirs is usually dependent upon basic factors of physical, chemical and biological conditions of the impound- ments, either singly or in combination. It was apparent that total standing crop is directly affected by surface area, shore develOpment, dissolved solids, outlet depth, and type of reservoirs. Sport harvest is inversely affected by surface area and age of the reservoirs. Commercial catch is negatively affected by mean depth, storage ratio, but positively with age of reservoirs. Plankton production influences I directly the survival of fish fry and the young, growth rate, and finally fish productivity. The ability to estimate fish production is very important in permitting management personnel to make a more accurate appraisal of the expected harvest from rbservoirs. Several methods of estimating fish production in lakes and reservoirs have been recommended with specific assumptions and variables. These methods include Hayes and Anthony's productivity index, Ryder's morphoedaphic index, and Jenkins' reservoir environmental concepts. All estimates are prOposed to interrelate the 193 physical factors to chemical conditions of the impoundment and then relate them to standing crOp or to the catch. The results of estima— tions showed various degrees of significance which mainly depends on quality of morphoedaphic conditions of impounded water and accuracy of records of the catches. THE STUDY OF UBOLRATANA RESERVOIR NORTHEASTERN THAILAND The Ubolratana Reservoir is located on the Pong River, 450 km northeast of Bangkok, Thailand. The project occupies a broad, flat valley among the gently undulating hills known as Phupan and Phupan Kam. It is a shallow 41,000 hectare reservoir with an average depth of 16 m at the minimum storage elevation of 182 m above mean-sea-level (MSL), and at its minimum elevation of 176 MSL, its surface area is down to 16,700 hectares with an average depth of 12 m. High water-level usually occurs in the rainy season and the low level in late summer. The lake bottom was, prior to inundation, mostly paddy fields inter- Spersed with shrubs and trees. The soil is characterized as relatively infertile, consisting of loams and sandy loams. Climate is character— ized by relatively long, hot, dry summer and moderate winter. The mean annual precipitation over the watershed is about 1,200 mm. The water— shed covers approximately 12,000 square-kilometers. The dam was closed in January 1965. It filled in 9 months. PRE-IMPOUNDMENT STUDY Prior to impoundment, Studies were conducted only on the ichthyo- fauna, none of the physico-chemical and other biological conditions being Studied because of limitations of staff and budget (Sidthimunka and others, 1968). They reported 76 species of fish were found, mostly the riverine Species.. The species composition was comprised mainly of carps (31 species, contributing 59.9% by weight) and catfishes (14 194 195 species, comprising 20.6% by weight), whereas all the rest comprised only 19.5% by weight (Table 13). The average yield (standing crOp) of fish caught by the rotenone method was 117.5 kilograms per hectare. Table 13. Percentage by weight of major groups of fish found in the Ubolratana Reservoir during pre- and post-impoundment periods Pre-impoundment Post-impoundment Major groups Number of Percentage Number of Percentage of fish species by weight species by weight 1 Carps 31 59.9 25 24.1 Catfishes 13 20.6 6 11.9 Murrels 4 7.0 3 34.8 Miscellaneous 28 12.5 18 29.2 Total 76 100.0 52 100.0 POST-IMPOUNDMENT STUDY Following impoundment, the temperature at water surface fluctuated closely with fluctuations of atmospheric temperatures. Dissolved oxygen decreased rapidly between the depths of 5 m to 10 m depth, whereas carbon dioxide increased. Even though no vertical temperature records were taken at this time, it was presumed that a thermocline might develOp t somewhere near the 10 m depth. This assumption was later confirmed by Shiraishi and Kimura (1971), who observed a thermocline in this reser- voir between the depths of 11 m and 13 m depth. Furthermore, they also observed chemical stratification similar to that of thermal stratification. Biological studies were conducted only once after the impoundment (Sidthimunka et al., 1968). They found Microcystis and Polycystis were dominant phytOplankton. There was eXplosive growth of aquatic vegeta- tion along the shore-line and in shallow areas (less than 6 m depth). 196 These aquatic weeds included coontail, CeratophyZZum dbmersum;‘bladder- wort, Utricularia flexuousa; hydrilla, Hydrilla verticillata;1vater hyacinth, Eichornia crassipes; water lettuce, Pistia stratiotes; floating waterfern, Salvinia cucuZZata; arundo, Arundb donax;xaater-smartweed, Polygonum tomentosum; and bulrush, Scirpus grossus. Zooplankton was dominated by protozoans, rotifers, and nauplii in summer (April), clado- cerans and c0pepods in the post monsoon month (November). Annelids, Chaoborus, chironomids and snails were the major groups of benthic organisms which were concentrated at the depths bewteen 2 and 6 m. Changes of icthyofauna were observed in one year after the impound- ment. Only 52 species were collected by the rotenone treatment after, compared with 76 species prior to impoundment. Of these, 44 species were pre-impoundment descendants; 8 species were newly added to the post-impoundment samples. Amazingly, post-impoundment samples were dominated by carnivorous species of murrels (Snakehead fishes). The murrels comprised 34.8% by weight compared with 24.1% for carps, 11.9% for catfishes, and 29.2% of other Species (Table 14). The standing crop was estimated at 177.7 kg/ha. Further investigations showed fluctuations in species composition of fishes in this impoundment. Numbers of species caught ranged from 76 species in 1965; 52 Species in 1966; 73 species in 1969; 58 species in 1970; to 67 species in 1971 (Table 14). It showed that several Species disappeared following the impoundment, such as Luciosoma bleekeml, Bamllius guttatus, Labeo bicolor, Cmssocheilus reba, Mekongina erythmspilla, Botia beauforti, Kryptotems bleekemi, Preropangasius cultratus, Mys tus wyckii, Bagamlus bagamlus, and Trichogaster microlepis. Many species became dominant in the reservoir such as Pristolepis fasciatus, Cyclocheilichthgs apogon, Trichogaster tmlchopterus, 197 Table 14. Pre- and post-impoundment fish species found in Ubolratana Reservoir, Khon Kaen, Thailand Pre- impound- ment Post-impoundment Scientific names 1965 1966 - 1969 1970 1971 1. Corica goniognathus (Bleeker) + — + + + 2. Notopterus notopterus (Pallas) + + + + + 3. Macrognathus acuZeatus (Bloch) + + + + + 4. Mastocerrbelus armatus favus Hora - - + + + 5. M. armatus armatus Gunther + + + - — 6. M. circumcinctus Hora - — + + + 7. FZuta aZba (Zuiew) — + + + + 8. Oxygaster omygastroidés (Bleeker) + - + - - 9. O. macuZicauda (H.M. Smith) - + - - — 10. 0. siamensis (Gunther) - + + - _ 11. Paralaubuca rivenoi (Fowler) + - + — - 12. CuZtrops siamensis (Hora) + + _ - - l3. ESovms metallicus Ahl. + + + + + 14. Luciosoma bleekeri Steindachner + - - — - 15. Rasbora heteromorpha Duncker + + - - — 16. R. borapetensis H. M. Smith - + + + + 17. R. argyrotaenia (Bleeker) + + + + + 18. R. trilineata Steindachner + + + + + 19. R. retmeI-salis H. M. Smith - + + — - 20. Mystacoleucus chilopterus (Fowler) - - + + - 21. Hampala macrolepidota van Hasselt + + + + + 22. H. dEspar H. M. Smith + + + + + 23. Cyclocheilichthys apogon (Cuv.&Val.) + + + + +_ 24. C. enopZos (Bleeker) + + + _ - 25. C. armatus (Cuv.&Val.) - + — _ - 26. C. repasson (Bleeker) + + + + + 27. Barilius guttatus (Day) + - _ - _ 29. Cirrhinus juZZieni Sauvage + - + + + 30. Puntius Zeiacanthus (Bleeker) + + + + + 31. P. sophoroides (Gunther) + - + _ _ 32. P. partipentazona (Fowler) + + + + + 33. P. gonionotus (Bleeker) + + + - + 34. P. viehoeveri Fowler - — + + + 35. P. orphoidbs (Cuv.&Val.) + + + + + 36. Puntioplites proctozysron (Bleeker) + - + + + 37. Osteochilus melanopleura (Bleeker) + - + + + 38. 0. dhostigma Fowler - - + + 1+ 39. 0. hasselti (Cuv.&Val.) + + + + + 40. 0. vittatus (Cuv.&Val.) + + — _ _ 41. 0. prosemion Fowler + - + - + 42. O. spilopleura Fowler - + - - _ 43. Larbiobarbus bumanicws (Day) - — _ _ _ 44. L. spilopleura (H. M. Smith) + + — _ - 198 Table 14 (cont'd.) Pre- impound- ment Post-impoundment Scientific names 1965 1966 - 1969 1970 1971 45. L. Zineatus (Sauvage) - — + + + 46. L. kuhlii (Cuv.&Val.) - — + + + 47. Mbrulius chrysophekadion (Bleeker) + - + + + 48. Later) bicolar H. M. Smith + - - - _ 49. L. erythrurus Fowler + + + - - 50. Lobocheilus quadrilineatus (Fowler) - + + + + 51. L. negnovittatus H. M. Smith - - + + + 52. Crossocheilus reba (Hamilton) + — - _ _ 53. Mekongina erythrospilla Fowler + - _ - - 54. Botia hymenophysa (Bleeker) + - _ + + 55. B. horae H. M. Smith + + - + + 56. B. modesta (Bleeker) + + - - - 57. B. beaufbrti H. M. Smith + - _ _ - 58. EpaZzeorynchos coatesi (Fowler) - - + - + 59. Acanthophthalmms javanicus Bleeker + + + + + 60. Acanthopsis chirorhynchas (Bleeker) + + + + + 61. Lepidbcephalus octocirrus (van + - + + + Hasselt) 62. Cobitophis anguiZZaris (Vailant) + + + + + 63. Noemacheilus pocuZi H. M. Smith + + - - — 64. WaZZagania attu (Bloch) + - + + + 65. Ompok bimaculatus (Bloch) + + + + + 66. Kryptopterus cryptopterus (Bleeker) + - + - - 67. K. apogon (Bleeker) + - + - + 68. K. bZeekeml Gunther + — _ _ _ 69. CZarias batrachus (Linn.) + + + + + 70. C. macrocephalus Gunther - - + - + 71. Pteropcmgasius cultratus (H.M. Smith) + - - .. - 72. Leiocassis Siamensis Regan + - + — + 73. L. albicoZZaris Fowler - - + - - 74. Mystus vittatus (Bloch) + + + + + 75. M. artifasciatus Fowler - - + + + 76. M. nemurus (Cuv.&Val.) + + + + + 77. ML wyckii (Bleeker) + - _ - - 78. M. guZio (Hamilton) + + - - - 79. M. cavasius (Hamilton) + + + + + 80. Heterobagrus bacourti (Bleeker) - - + - + 81. Bagarius bagarius (Hamilton) + - — - - 82. Xenentodbn cancila (Hamilton) + + + + + 83. Synaptura aenea H. M. Smith + — — _ _ 84. Anabas testudineus (Bloch) + + + + + 85. Trichopsis vittatus (Cuv.&Val.) + + + + + 86. T. challerii H. M. Smith - - — + + 87. Betta splendbns Regan + - + + + 88. Trichogaster microlepis (Gunther) + — — _ - 199 Table 14 (cont'd.) Pre- impound— ment Post-impoundment Scientific names 1965 1966 - 1969 1970 1971 89. T. trichopterus (Pallas) + + + + + 90. T. pectoralis (Regan) + — + + + 91. Ophicephalus striatus Bloch + -+ + +' + 92. 0. gaahua Hamilton + + + + + 93. O. Zucius (Cuv.&Val.) + - + + + 94. 0. micropeltes (Cuv.&Va1.) + + + + + 95. Chanda wolffii (Bleeker) + + — _ _ 96. C. siamensis Fowler - - + + + 97. Pristolepis fasciatus (Bleeker) + + + + + 98. Nandus nandus (Hamilton) + + — _ - 99. N. nebulosus (Gray) + — + + + 100. Oxyeleotris marmoratus (Bleeker) + + + + + 101. Tetraodbn Zeiurus Bleeker + - + + + *102. Foobanbus juZZieni Sauvage - - - — + *103. Cirrhinus nvlitorella (Cuv.&Val.) - - - — + *104. Ctenopharyngodbn ideZZa (Cuv.&Val.) - - - - + Total species 76 52 73 58 67 + - present species = absent species introduced species stocked in 1971 a. ll Trichogaster pectoralis, Osteochilus hasseZti, Notopterus notopterus, HampaZa dispar, Puntius Zeiacanthus, Ophicephalus striatus, and Ophi- cephalus Zucius (Table 15). Some species were found only in post- impoundment samples such as Mastocembelus circumcinctus, Rasbora borape- tensis, Puntius viehoeveri, Osteochilus duostigma, Lambiobanbus Zineatus, Loboaheilus quadrilineatus, Clarias macrocephalus, Mystus artifasciatus, and Chanda siamensis (Table 14). The fluctuations may occur due either to insufficiency of sampling method (rotenone) and collected samples or to accidental infiltration from other areas. The infiltration of fish may occur by means of changing physical conditions; for example, a heavy 200 rain on the watershed areas and the wind actions, as well as by the activities of animals and man. Table 15. Total yield of dominant species taken from Ubolratana Reservoir by the rotenone method (weight in kilograms) 1969 1970 1971 E- E- E- Species Weight value* Weight value Weight value PristoZepis fasciatus 26.47 22.40 38.78 12.26 67.91 17.66 Cyclocheilichthys apogon 16.75 14.17 22.74 7.19 41.79 10.86 Trichogaster triahopterus 0.38 0.32 33.37 10.55 30.75~ 7.99 Trichogaster pectoralis 3.16 2.68 33.01 10.43 48.44 12.60 Osteochilus hasseZti 7.73 6.54 8.73 2.76 10.74 2.79 Notopterus notopterus 4.60 3.89 12.75 4.03 9.05 2.35 HampaZa dispar 2.24 1.89 10.57 3.34 10.65 2.76 Puntius Zeiacanthus 0.68 0.57 7.85 2.48 10.44 2.71 Ophicephalus striatus 7.11 6.01 57.57 18.20 53.25 13.84 Ophicephalus Zuaius 3.41 2.89 17.14 5.42 13.20 3.43 *E-value represents percentage in weight of given weight of total catches. STANDING CROPS Species to The stimation of standing crop of the Ubolratana Reservoir is based on data collected from rotenone treatments, which was the only source of data. Even though this method gives roughly estimated yield of the water body as a whole, it can be used to measure of annual relative abundance of fish to give some idea of fish production tendency. It was apparent that the standing crop of the Ubolratana Reservoir rapidly increased during the first two years after impoundment. Thereafter, the yields continuously decreased to a minimum in 1970 and then again tended to On the other hand, the commercial catches per unit increase in 1971. surface area have increased continuously since the impoundment. The 201 catch in 1971 was approximately 4-1/2 times greater than that of the first year after impoundment (Table 16). However, this prOportion may be reduced if the percentages of important fish groups of the annual commercial harvests are the same as prOportions of the annual standing crop. Table 17 Shows the percentage of catfishes is much lower in standing crop than in commercial catches. This disparity may result in lower estimates of standing crOp than it Should be, and also alters percentages of other groups to higher values. Low yield of catfishes in standing crOp may derive from inadequate sampling methods. The catfishes usually remain inactive in deep water or in Shelter during the daytime since they are bottom dwellers as well as nocturnal species. Therefore, they are less affected by rotenone treatments which are always applied in the day and in shallow water. COMMERCIAL CATCHES The commercial catches from Ubolratana Reservoir were recorded beginning with the commercial fisheries in this impOundment. Records of fish landing were collected at 3 landing centers: The Rua, Ban Kong Klang, and Ban Fah Lium, all stations in Khon Kaen Province. Total weight of fresh fish and processed fish (smoked, salted, and fermented fish) were daily recorded in separate groups. Those of processed fish were con- verted into weight of fresh fish by multiplying with a specific constant. - The ratios used in converting weight of processed fish to weight of fresh fish are 1:3, 1:2, and 1:0.8 for smoked fish, salted fish, and fermented fish (Pla Ra, Pla Som, etc.), respectively. Data showed annual increase in fish landing since 1965 through 1971, with the exception of a slight decrease in 1970 (Table 18). Records on monthly catches showed seasonal fluctuations and varied from year to year. They usually increased during J- oouooooom some coumu Hmfiouoano cocoa o haze « Ama\msv mm.~m mm.km sm.am ms.am m.NN «NS.HH - auumo Hmaonoaaoo Aae\mxv No.ee mm.ss om.sa mm.aoa oa.mma so.kka we.kaa aoou waaaamum Haas game some some teas seas mama Same» umow Humalmoma weapon .pcmawmeh .comM comm .uHo>ummom mamumuaoob ca coumo Hmwouoano was Awawaeemm ococmuouv mono wcflocmum oomsuoc aficmco«umamm .oa manna 203 oa.sa sNo.NNN mm.Nm aem.msN Hm.mN Nms.omm msouaaaauumaz No.s Nms.NN No.m mmm.aaa oa.aa msm.moa masons: Na.a mmm.NaN am.oa oao.osa NN.HH s~m.ma mannamumo noose Na.NN Nee.oam.a ss.m~ aoa.s~m No.ms Hom.NNs manmo Hmaunmaaoo ma.mm mm.NHN ma.mm Ha.msa om.mm os.am anomamaamomaz Hw.sa Nm.mN ms.mm No.0w No.sa os.ea masons: ow.~ SS.OH mo.~ oe.w om.a om.a nonmamumo aouo os.NN Hm.Hw NN.mH om.am ma.am oo.oo mango massamum N Awsv names: N Aass Samoa: N Away sesame masons same» HNaH oNaH seas unmet QDHN> ummw OHBosoom HNaauasaa weapon .ocmaamcy .oomz coax .uHo>ummom mcmumuaoob aouw cmflw mo mwsfimsouw uaaocoom snow mo Amoaumwumum cameo Hmoocmv comma Hmfioumsaou pom Awsaamamm moosoaouv mono wcfipcmum mo somaummaoo .NH macaw 204 Haw.mea.m mmm.omm.H ssN.ooa.N ome.ao~.a mmm.saa sam.mNs zooms Nance mmo.mm oma.mm moa.sa Noo.sa ass.~m sam.om “monsoon moo.oHH ooe.NN ses.ae mms.sa ssN.No smm.o~ nmnam>oz NNN.NSH mam.aoa Nao.Na NNH.¢NN Hma.saa smo.oo umsOSUO aao.maa Noo.aoa mmo.NeH HNN.SNH sHN.oaH NNN.smH nmnamunmm New.sam Nsm.me ems.osa mma.aaa mas.SNN ess.mma “mamas mam.NHm NNN.ama ome.m- oms.asa «SN.mHH ams.moa Nose mmm.oa~ moa.osa maN.mNN Haa.NmN asm.ao . mass mNo.NNN mmq.eoa oma.amm wHN.moa oom.as . as: ooN.smH Nss.NoN eso.mmm mmm.mm Nmm.mm . Hanna maa.sma amm.aoa wa.mma mo~.mo mN~.mN u nous: Nsm.NoH sas.ma Naa.oom ooo.mm Nam.ma . Nnmsnnmm mms.ooa NHN.am Nao.saa mNs.~m smo.a~ . stanzas HNSN oNaH some some Nose some case: use» Amamnmoaax no ucwH03v Humalooma wofiuoo .pamafimch .cmmx coax .uao>uomom mcmumuaocb Eouw coumu Hmfioumaaou Hmuoe .wH oaome 205 the dry period, May to September, and decreased during high water-level period, October to April (Figure 13). When plotting monthly commercial catches against average monthly water—level reciprocal, a reverse rela- tionship is obtained (Figure 14). This relationship may indicate that at low water-level fish were concentrated in the maintaining pool which brings them into closer contact with the fishing gears, thus increasing the chance of being caught. Unfortunately, there are no records in detail on variations in numbers of fishermen, types and numbers of fishing gears at different times of the year and of different years. Shortage in data makes comparing catch per unit of effort or determining tendency of production inaccurate. Therefore, it may not be reasonable to conclude that an increase in commercial catch per unit area is the result of increase in fish pOpulation, since high catch can also obtain from increase in fishing intensity, higher efficiency of fishing gears and their Opera— tions, and/or the combination of these factors. FISH TRANSPLANTATIONS In order to provide more fish food and utilize all levels in the food chain in the newly created reservoir, intensive transplantations have been made as early as during the period of filling the impoundment. A thousand grass carp, Ctenopharyngodbn ideZZus, fingerlings (10.0 cm); 579 Silver carp, Puntius gonionotus, fingerlings (8.0 cm); and 20,000 fingerlings (5.0 cm) of Snake-skinned gouramy, Triahogaster pectoralis, were stocked in Ubolratana Reservoir by the Department of Fisheries. The latter species was found continuously dominant in the impoundment since 1969 (Table lS);the others are not yet found in significant numbers in this reservoir. In 1970 additional transplantations were made with 206 .d. as $883 3 £3 33. magnet .wsmaamce .oomx song .uao>uomom mamumumonb aoum coomo Hmwouosaoo hauaoz. .mH Shaman . Han Omma mcma mead o.H coma l l l l 11 mm I we 1.00H I mNH I omH r.mmH 1.00m x.mNN v.0mm 1 mum Ioom Immm 0mm (38x 000‘1) qoneo TBIDJOmmOQ 207 Water-level fluctuations in meters above mean-sea—level comma Hmauuoaaoo pom mSOfiumauuon Ho>malumuos.aw9ddm smmsaoo.dficmcoaumamu mcH .Hmma nonaounom ou cmma Honouoo wofiuao .oomafimck .sOmM coax .uao>uooom monumuaonb OH .sH mosses HNaN_ oNaH .umom .w=< >Hoh moon he: .se< .umz .com .mmw .uoo .>oz .uoo WNH m P — _ p _ e _ _ _ _ p O tom cmal Aroo seal mCOHumouooam vom Ho>oalumum3 Toma weal. Iowa romH meal 10am owal roam 105m amen Icon IoEEt\o NmH l M: OH.» .r 0mm com (38x 000‘1) qoneo {stalemmoo Atqnuon 208 3,379 grass carp of 24.8 cm average total length and 10,303 Chinese carp, Cirrhinus malitoreZZa, of 20.3 cm average total length. Five more thousands Cirrhinus nolitorella (16.0 cm); 7,000 Aristiahthys nobilis (11.6 cm); 8,400 catfish, Pangasius sutahii (18.3 cm); and 10,000 carp, Probarbus juZZieni (10.0 cm) were added in 1971. The introduction of all these fish had no influence on Species composition or total yield (commercial catch). So far less than 1% of stocked fish have been caught and reported. However, it is very interesting to know that some introduced species have shown a great growth rate. The grass carp reaches weights up to 12.4 kg in 2 years, the Cirrhinus molitorella weighs 7.4 kg in 1 year, and Probambus juZZieni weighs one-half kilo- gram in 7 months after stocking (Pholprasith and Waiwutto, 1971), other species have not yet been recovered and reported. CONCLUSIONS AND RECOMMENDAT IONS The Ubolratana Reservoir is an important source of protein food for people of the northeastern Thailand, in situ; it also provides the rural inhabitants a new occupation--of course, the fisheries. Prior to the time the dam was built, fish were caught in small amounts as part of a subsistence life of most of the rural inhabitants; only a few were left for sale. At that time, although fish were abundant in terms of quantity of fish per unit area, the geographical distribution patterns were not favorable to intensive fishing. Generally, the fish- ing season in this part of the country more or less coincides with the rainy season, beginning in May or June and ending in December or January when the paddy fields, swamps, and most of the natural water bodies dry up. As soon as the Ubolratana Reservoir was impounded in 1965, many rural inhabitants, mostly rice farmers, became full-time 209 fishermen. The numbers of fishermen using this reservoir have increased from an averaged 200-300 families in 1966 to approximately 1,100 families in 1971. This year (1971) they caught fish out of the Ubolratana Reservoir amounting to more than 2,165 tons; its value exceeded 18,000,000 Baht ($1 million). In order to maintain this reservoir as an ideal fishery resource, studies must be attempted to examine all ecological changes which affect the fauna and flora of the inundated areas. So far records have been made mainly of species composition of fish and yield from commercial _catches. None of the physico-chemical and other biological changes were measured or estimated. It is necessary to carry out both physical and chemical analysis of impounded water and to keep records of water- level fluctuations, temperature, turbidity, hydrogen-ion concentration, dissolved oxygen, carbon—dioxide, alkalinity, and dissolved salts. The values of these factors together with knowledge of plankton and benthos composition and abundance are very important in planning management programs, since efficient management based on sound data is essential for ensuring maximum production of fish. In management programs, attention should be given to controlling the growth of aquatic macrOphytes. Fortunately, problems are not serious with Submerged species Since they usually disappear after the flooded period as a result of high turbidity inhibiting their photo- synthetic activities. Trouble occurs with overgrowth of floating aquatic plants particularly water hyacinth, Eichornia crassipes; water lettuce, Pistia stratiotes; and water fern, SaZvinia aucuZZata. These plants tend to form mats which interfere with fishing, navigation, recreation, operation of powerplants and crop irrigation, and prohibit growth of phytOplankton underneath. Up to now, the Electricity Generating 210 Authority of Thailand (EGAT) which is in charge of the reservoir maintenance has done very little to control the aquatic vegetation especially the water hyacinth. It seems understandable as the weeds do not at least for the time being interfere to any substantial degree with the generation of electric power. More attention has been given by the Department of Fisheries. Some means of biological control has been instituted. Many species of herbivorous fishes have been intro- duced into the reservoir; for example, the grass carp, Ctenopharyngodbn ideZZus, and Thai silver carp, Puntius gonionotus. Other species may be introduced for this purpose, including the Congo tilapia, TTZapia melanopleura; Nile tilapia, T. nilotica, T. ziZZii; and Chinese silver carp, Hypophthalmichthys ”blitrix. These species adapt well to climate conditions in Thailand and have a good growth rate. However, herbivorous fishes contribute good control of only the Submerged aquatic plants, they have little effect on floating and emergent species. Therefore, other biological agents such as the flea beetle, Agasicles Sp.; weevil, Neochetina sp.; leaf minor, Crytobagous singularis; and freshwater snail, Marisa cornuarietis, Should be carefully studied in experiments at the laboratory level to find out possible application for aquatiC~ plant control in Thailand. Experiments using these biological agents for controlling aquatic plants are in progress in Argentina, Trinidad, and the United States. However, these projects are time consuming and other means, either mechanical or chemical control, should be considered when favorable with geographical conditions, budget, and personnel. Extensive education about using aquatic plants such as water hyacinth and coontail to feed livestock (swine and cattle) should be considered. Success has been observed in the northern Thailand where intensive use for animal feeding in large quantities is sufficient to control its growth and spread. 211 The fluctuations of water level in Ubolratana Reservoir seem to be less important in fishery management than in reservoirs in temperate regions. It cannot be used effectively either for eliminating unde- sirable fish or for prohibiting growth of nuisance aquatic vegetation. The reasons are that fish in tropical waters usually spawn at least once annually and many Species Spawn several times a year. They have a wide range of Spawning season which starts as early as the beginning of the rainy season (June or July) when the water level is rising with more fresh and cool rain water, and ending in September to October when monsoon cease. There are also great variations in Spawning time for species that spawn more than once a year depending upon their geno— typic characteristics and environmental conditions. In fact, there are too many species in this reservoir and their spawning times are rela- tively close together, so several species overlap. Therefore, it seems to be impractical to attempt to eliminate a given undesired species by means of water level management because many other Species will also be destroyed. In aquatic weed controls, it is apparent that the abundance of submerged aquatic weeds Showed a reverse relationship with the water level in this reservoir. During the period of high water level (flood- ing period), water became brown in color with dissolved materials and suspended matter. This turbid water reduces light penetration into the water to cut off photosynthetic activities of submerged plants. The turbidity takes over for several months in the rainy season, which is long enough to cause the submerged plants to partially or totally 4disappear. 0n the other hand, explosive growth of submerged aquatic weeds occurs in the summer months with low water level in the impound- ment. During this low water period, storage water is conserved for the purposes of power generation and irrigation for the coming rice cultivat- ing season. 3- 212 The introduction of new fish species to the Ubolratana Reservoir is mainly for the purposes of providing more food fish available to the people, for increasing the capacity of the impoundment by utilizing excess food not used by the local species, and for controlling aquatic vegetation. The grass carp, Thai Silver carp, and the snake-skinned gourami were introduced as soon as the dam was closed. Later, plankton feeders, Cirvhinus moZitoreZZa, and Aristichthys nobilis, were stocked. Pangasius sutahii and Probanbus juZZieni were introduced to feed on benthic organisms and freshwater snails. Although many of these species showed very good growth, we need to know more about how they affect native species. Are they able to reproduce in this impoundment? These problems confront the fishery biologists and need to be solved prior to introduction of other fish species to the water body. In case of the Ubolratana Reservoir, at least so far, only limited and incomplete data of physico-chemical and biological conditions other than species composition of fish and commercial catches are in hand. In fact, these data cannot be used as a tool for consideration of fish transplantation programs. Luckily, most introduced Species have their feeding habits related closely to the base of the food chain and are accepted by peOple as food fish. Therefore, any possibility of danger to the fisheries as a whole may not be a serious prOblem. It may be useful to recommend here that in future transplantation programs Should be done after thorough studies of physical and chemical conditions together with biological changes within the impoundment and the tributaries. It should be kept in mind that a species which is introduced Should not only possess a good growth rate, but be compatible in the new environments and other fish species. It must be able to reproduce naturally in the new water body. Former studies have shown that none of the Chinese carps except 213 the common carp, can breed naturally in the climate conditions of Thailand. Therefore, transplantations should be stressed only for fish that can reproduce in this reservoir in order to save time and reduce cost of additional stocking. Although there are no records on primary production and secondary production of zOOplankton and benthos of the Ubolratana Reservoir in hand, it is quite interesting to consider introducing live-food into this impoundment for providing more food to valuable species such as Notopterus notopterus, Osteochilus hasselti, GchocheiZichthys apogon, Pm’stolepis fasciatus, and Tmlchogaster triahopterus, as well as the young of most Species. Several invertebrates have been introduced successfully into reservoirs of many countries around the world, especially the Soviet Union, Canada, and the United States. Inverte- brates that give high promise for this purpose include cladocerans, amphipods, mysids, polychaetes, and molluscs. Unfortunately, there are no reports of experiments and successes of introducing these inverte- brates into trOpical reservoirs. The success of introducing Mysis relicta to reservoirs in southern California may be a good example for eXpanding this technique as a management tool applied to reservoirs under trOpical conditions. In case of the Ubolratana Reservoir, it may or may not be desirable to introduce additional live-food. Even though records on live—food supply are not available, the fluctuations of water-level cause alternate flooding and drying of at least one-half of its maximum surface area annually. This type of alteration enriches impounded.water with nutrients leaching from the soils to encourage the growth of phytOplankton, algae, and aquatic macrophytes. ZOOplankton usually increase their abundance in a short period after the blooms of phytOplankton. Benthos may reduce in number per unit surface area as a 214 whole because they have limited time for development in shallow areas near the shoreline which are quickly exposed to the atmosphere when the water-level decreased. Abundance of food supplies in the Ubolratana Reservoir may be inferred from the tremendous increase in numbers and growth rate of Trichogaster‘pectoralis, Trichogaster triahopterus, Osteochilus hasselti, Cyclocheilichthys apogon, Pristolepis fasciatus and all introduced Chinese carps. This evidence may indicate that this reservoir produces food in excess of consumption by native fish, and is left to support amazing growth of newly introduced species. It is accepted that fishing has various effects onfish pOpulation particularly when fishing is carried on at the wrong time of the year or with damaging methods. Therefore, it generally is necessary to have some means to measure the control of fishing for desirable and protected fish pOpulation. In the case of the Ubolratana Reservoir, fishing is allowed everywhere all year long. The gill net is by far most popular fishing gear, others including lift net, cast net, hoop net, hooks, harpoons, and various types of bamboo-traps. With these types of fishing gear, there is no need to have any regulation on their Operations because they are stationary fishing gear which usually cause no damage to the fisheries. However, attention should be given to the control of some fishing gears and fishing practices in certain parts of the reservoirs, particularly during spawning season to prevent undue dis- turbance of spawning stocks and/or eggs and larvae. Regulation of mesh size may be impractical in this reservoir since the fisheries bear on multi-species resources making difficult the designing of apprOpriate mesh Size to ensure adequate catch. Restriction should be imposed on destructive fishing methods such as the use of poisons and explosives. 215 DISCUSSION The objective of fishery management in the Ubolratana Reservoir is to provide food fish to local peOpIe for their well being. Fish trans‘ plantation has been an intensive program in this impoundment. Several fish species were introduced for the purposes of providing more food fish to pe0p1e, increasing productive capacity of the impoundment, and controlling aquatic vegetation. Success has been found only on the introduction of Triahogaster pectoralis; others have not yet been reported. Even though a couple of species have Shown good growth rate, they still are not significant in species composition or of the catches. The management of the fish population in this reservoir has to be a wide range program. It cannot be a success if management stresses only a given species or a few important ones because the fisheries in this reservoir depend on many species of fish. There are too many fish species in this impoundment, making difficult or impossible a manage- ment program for any specific Species without interference with other valuable ones. Such a program may not be desirable for this reservoir since the rural inhabitants exercise almost no selection in species and size of fish for their food. All species are accepted, however, in, various degrees of preference. There are no selective fishing practices Operating in this reservoir. Thus, there is no problem of overcrowding with low value Species or nuisance fish as one encounters in temperate regions such as the carp problem in reservoirs of the United States. A possible management progarm may be exercised by restriction of fishing practices in certain areas at the spawning period of valuable species for protecting their spawning activities as well as eggs and larvae. This technique may be an effective practice in fish management in this type of situation for ensuring adequate recruitment to the fisheries in. years to come. 216 The fishery develOpment in the Ubolratana Reservoir is still in the initial phase of high productivity. A decline of fish production may appear soon as the normal cycle of reservoir productivity eXperienced in all parts of the world. In general, a decrease in fish production in reservoirs following initial high production is a result of nutrient shortage for organic matter synthesis. It occurs whenever nutrients are in short supply from inundated soils as a result of nutrient.loss to bottom sediments, outflows, and the removal from the reservoir as fishery products. However, this phenomenon usually occurs in deep reservoirs with limited water-level fluctuations. In the case of the Ubolratana Reservoir this problem may not occur because it is a shallow lake with a wide range of water-level fluctuations which expose at least one-half its maximum surface area to dry up annually. When it floods again in the rainy season, nutrients are leached from the soils and decomposed organic matter to encourage photosynthetic activities and the growth of zOOplankton and benthos. Therefore, attention should be given to the study of environmental changes. Knowledge of the physico- chemical factors (such as annual water-level fluctuations, thermal Stratification, dissolved salts) and biological conditions (species composition and abundance of phytOplankton, ZOOplankton, and benthos) makes it possible to predict the tendency of fish production in this impoundment. Such knowledge is required in planning management programs for maintaining this reservoir as an ideal fishery resource. SUMMARY The construction of dams either for the purpose of electropower generation, irrigation, flood control, or water supply has many effects on water quality. Studies have shown that after the dam is closed the prOperties of water change both physically and chemically. These changes affect biological activities in the reservoir and in the river below the dam. The quality of impounded water usually depends upon characteristics of the dam site, inundated areas, the soils, and fluc- tuation of climatic conditions. Furthermore, it is also affected by type of reservoir and its morphometric characters, such as surface area, depth, and shoreline develOpment. Several physical factors of the water are altered following the completion of the impoundment. A reservoir usually acts as a settling basin and reduces the turbidity of water. As a result, light penetra— tion in an impoundment is greater than in a river upstream. Temperature is increased because of longer time eXposure to the sun, particularly in shallow waters and the upper layers of reservoirs with great depth. Differences in temperature gradient of a water colum result in a thermal stratification of 3 layers, the epilimnion, thermocline, and hypolimnion. The develOpment of thermal stratification in reservoirs usually occurs in different patterns, depending on geographical loca- tion, climatic conditions, depth, surface area, outlet design, and hydrology of the inflows. Many types of thermal stratification have been found in reservoirs either during the summer or winter months. 217 218 During stratified periods, a lower oxygen supply in the hypolimnion, or increase in carbon dioxide and noxious gases such as hydrogen sulfide and ammonia often results. These conditions cause severe problems to aquatic animals living in the hypolimnion. Attention has been given for solving this problem. To date, artificial destrati- fication showed most effect in water quality improvement. It not only has a benefit of improving water quality in the reservoir itself, it also improves water quality in the river below the dam. The enlargement of water surface together with warmer water in reservoirs increases the loss of water through evaporation. It leads to deterioration in water quality due to the increase of salt concen- tration and suspended materials, and eliminates its use for public consumption and recreation. High turbidity restricts penetration of light; therefore, it tends to inhibit the growth of phytoplankton and algae. It may also lead to develOpment of chemical stratification or turbidity currents and an increase in the rate of sedimentation. Sediment accumulation in reservoirs not only affects life expec— tancy and its economic value, it also influences biological activities in many ways. It may destroy spawning grounds of several Species of fish and eliminates benthic organism habitats. It is also effective in removing oxygen from the hypolimnion by decomposition activities. It may limit nutrient exchange between the bottom substrates and the overlying water. On the contrary, sediments that contain high concen- tration of nutrients if released will stimulate growth of phytoplankton and algae. The fluctuation of water-level in reservoirs has a dual character. A decrease of water-level may destroy benthic organisms by exposing them to the atmosphere, destroys spawning grounds of many fishxspecies, _L' 7 o. I 219 and also eliminates feeding areas and shelters for the young. Rising water-levels flood meadows and swamp vegetation, resulting in decompo- sition, thus releasing nutrients to impounded water stimulating the growth of bacteria, phytOplankton, and ZOOplankton which serve as food for fish. Manipulation of water-level can be used as an effective technique in controlling aquatic weeds as well as managing fish pOpu- lations in reservoirs. Evidences have been discussed. The concentration of dissolved oxygen in reservoirs decreases considerably during the filling period as decomposition of flooded vegetation and other organic matter occurs. Following the initial low oxygen content, it tends to increase by agitation as well as photo- synthesis. Dissolved oxygen is not a critical factor in shallow reservoirs, but it may cause a serious problem in the hypolimnion of stratified reservoirs if its concentration becomes depleted. Decompo- sition of organic matter under anoxic condition causes a build-up of carbon dioxide, hydrogen sulfide, and ammonia, all of which are limiting factors to aquatic animals. Carbon dioxide is not only a major factor affecting the buffer system, it also plays an important role in regulating eutrOphication in reservoirs. Moderate increases of carbon dioxide will increase primary productivity in the impoundments, but at high concentration may be definitely limiting to aquatic animals. The changes of carbon dioxide by photosynthetic and respiratory activities fluctuate acid— base relationships, particularly with relation to the hydrogen-ion concentration. There are great variations in concentration of biogenic salts in reservoirs. It usually varies with geographical location, water runoff, domestic and industrial wastes, fertilization of farm lands, and the 220 inflow contents. It generally appears that nitrogen occurs either as dissolved organic nitrogen or as inorganic nitrogen such as ammonia, nitrite, nitrate, or as elemental nitrogen. Ammonia and nitrate are most important sources of nitrogen for growth of phytoplankton, bacteria and algae. The concentration of nitrate decreases with phytoplankton blooms, while an increase of ammonia is associated with a decline of phytOplankton. The concentration of phosphorus generally Shows an increase with ‘ age of reservoirs. Phosphorus is an important element for the growth I of vegetation. In reservoirs, a great decrease in total phosphorus L and soluble phosphate always appears at times of algal blooms, and El ‘ increases when it declines. It appears that bacteria play an important role in making phosphorus available for the growth of aquatic vegetation in reservoirs. Sulfate concentration is usually low in freshwater reservoirs. Its concentration under aerated conditions increases with depth but decreases in anaerobic condition as a result of its reduction to hydrogen sulfide. Iron generally occurs in impounded water during the stratification. qak‘ Whenever water is devoid of dissolved oxygen, ferric oxide will be I reduced to the soluble ferrous-ion. Manganese is found in high concen- tration only in certain regions such as the Piedmont plateau of the tfil‘ southern United States. Its concentration usually increases in the hypolimnion during the stratification. These elements are considered as limiting factors to primary productivity in lakes and reservoirs. Since the eutrOphication increases with age Of reservoirs, the growth of aquatic vegetation will increase and interfere with their uses. Therefore, attention has been given to prevent this condition by means of nutrient removal from impounded water and the influents. Several 221 procedures have been tried, and they showed different degrees of removal and costs. The development of phytOplankton in reservoirs begins as the lacustrine species become increasingly abundant after closure of the dam. Blooms occur during the first few years after the impoundment as favorable conditions for their growth develOp in reservoirs following the closure of the dam. These conditions include slow current and prolonged detention time, warmer water temperature, reducing turbidity, increasing depth of light penetration in water, and higher nutrient content in impounded water. However, their production fluctuates with locality and season. In temperate regions, the minimal numbers occur in winter and mid-summer, the maxima in spring and fall. In the tropics, the maxima usually occur in post winter and after the monsoon months, the minima occurring in winter and rainy season (monsoon months). Aquatic macrophytes invade reservoirs immediately after the closure of the dam. The emergent Species begin to develOp along the shore and in shallow areas; submerged plants occur in all photosynthetic depths; and floating Species Spread over the surface area. These aquatic plants Fa continue spreading with age of reservoirs. Large amounts of aquatic weeds affect reservoirs in many ways, such as by elimination of navigation and recreational uses, promotion of loss of water through Lg water replacement and transpiration, and creation of deoxygenated condi- tions. On the other hand, they may provide suitable habitats for spawning to fish and shelters for the young as well as habitats for periphyton and invertebrate organisms. The formation of the ZOOpIankton community in reservoirs begins in the short period after the impoundment. Species composition and their abundance vary with the morphological factors and the physico-Chemical 222 conditions of the impoundment and season. In general, the standing crop of ZOOplankton in a reservoir increases as the water approaches the dam. A sharp increase of the biomass of zooplankton usually occurs following the blooms of phytOplankton and bacteria which serve as their food. Fluctuations in their composition and numbers vary with locality and season in different years. The changes are also effected by the variations of environmental conditions of different areas within an impoundment. Rotifers usually dominate in the upper reach, the middle stretch is dominated by cladocerans and c0pepods, while the lower reach is dominated by cladocerans especially Daphnia. The total biomass of zOOplankton in most reservoirs occurs in the middle and lower sections. The develOpment of benthic communities in newly created reservoirs usually begins with a drastic decrease of rheophilic species and coin- cides with the strengthening of limnophilic species (Chironomidae, Oligochaeta, and Cladocera). The distribution and abundance of benthos in reservoirs is influenced by characteristics of the SUbstrateS, the biology of individual Species, the effect of predation, and physico- chemical conditions of impounded water. Studies Show that as these conditions develop in reservoirs they have a tendency to suppress either directly or indirectly the species composition and relative abundance of benthic organisms. The formation of fish pOpulations in reservoirs is usually accom- panied by a strengthening of the limnOphilic species, and the suppression or complete disappearance of the rheOphilic species. A decline of riverine Species is a result of changes in environmental conditions that does not favor them. For instance, the presence of the dam blocked their way to spawning areas, sedimentation reduced or completely destroyed their spawning grounds and reduced food supply to the 223 benthOphagous fish species. These conditions are favorable to limno- philic species by supporting a good growth rate, successful reproduction and survival rate. Thus they rapidly increase both in numbers of individuals and total biomass. Evidences indicate that the period of filling (in years) is a major factor controlling the Strength of year- classes during the initial develOpment of fish populations in reservoirs. A longer period showed a larger number of year-class Strengths. After the filling period the strength of year-classes fluctuates with environ- mental conditions, particularly the fluctuation of water-levels. The production of fish in reservoirs usually reaches its maximum within the first few years after the impoundment. Then it declines rapidly in following years to a much lower level which may be maintained or will gradually rise to somewhere near half the magnitude of the initial high productivity. The decrease is the result of the initial wealth of nutrients being used up in biological syntheses, no additional nutrient supply from inundated areas, the loss by nutrients being locked up in the bottom sediments, and the loss through the fishery products being removed and by the water discharges. In order to adjust the yield and maintain its fluctuating—fish production at a high level near the optimum productivity of the reser- voir, several management techniques have been practiced with different degrees of success. These promising activities include the manipulation of the habitats, the management of fish populations and their food supply, and regulation of the fisheries. Manipulation of habitats is mainly associated with the modifications of Spawning grounds and feeding areas, and the control of excessive growth of aquatic weeds. Knowledge of species composition, distribution and the abundance of fish, including biology of individual species, is 224 extremely important in management programs. Practical management techniques of fish populations based on these sound data are believed essential for ensuring maximum production of fish. Successful manage- ment techniques of fish pOpulations in reservoirs include: (1) selective killing undesirable species; (2) fish transplantations; (3) introducing food organisms into reservoirs to establish more food for valuable Species; (4) regulation of water-level and the tailflwater; (5) elimina- tion of fish parasites and diseases; and (6) by fishing regulations and F1 controls. It is evident that most reservoirs have greatly increased fish production over river conditions in all parts of the world. The produc- _.;a 4“. ' A . tion of fish usually fluctuates from year to year after a typical pattern of initial high productivity. Its fluctuation is mainly correlated with the changes of environmental conditions, length of the food chain of valuable species, and the success of management activites. In the United States, it is apparent that total standing crOp of a reservoir is directly correlated with surface area, shore develOpment, dissolved solids, outlet depth, and types of rbservoirs. Sport harvest is ’1 inversely affected by surface area and age of the reservoirs. Commercial catch is negatively affected by mean depth, storage ratio, but-posi- tively with age of reservoirs. The abundance of plankton influences hi. directly the survival of fish fry and the young, growth rate, and fish ); productivity. This study leads to the prOposal of possible management techniques for improving fish production of reservoirs in Thailand. The Ubolratana Reservoir in northeastern Thailand has been chosen for this purpose. It is a shallow reservoir with the surface area of approximately 102,500 acres and an average depth of 16 m at maximum water-level. The dam was 225 closed in 1965. Investigations during pre- and post-impoundment stressed mainly the changes of species composition of fish and the commercial catch Statistics. Only a few records were made on the physico-chemical conditions and other biological develOpments. These inadequate data made it difficult to prOpose specific management programs for the fishery develOpment of this reservoir. So, recommendations are dis- cussed in general based on general problems that usually occur in reservoirs in all parts of the world and particularly on those reser- fil_ I voirs in the trOpics. 10. LITERATURE CITED Aass, P. 1960. The effects of impoundment on inland fisheries. Pp. 69-76. In the Seventh Tech. Meet. of IUCN, Theme 1, Vol. IV. Athens, Greece. Adesanya, Z. A. 1969. Problems of fish production in man-made lakes. Pp. 204-205. In Man—made Lakes. L. E. Obeng (ed.), The Accra Symposium. Ghana Universities Press, Accra. Aggust, L. R. 1971. Summer benthos in newly flooded areas of Beaver Reservoir during the second and third years of filling 1965-1966. Pp. 139-152. In Reservoir Fisheries and Limnology. G. E. Hall (ed.), Am. Fish. Soc., Spec. Publ. No. 8. Alasbaster, J. S., and B. Stoot. 1967. Grass carp (Ctenopharyn- godan ideZZa Val.) for aquatic weed control. Pp. 123-126. In European Weed Research Council, Symposium. Allen, E. B. 1970. Pool fluctuation in crops impoundments in relation to fish spawning. Proc. Twenty-third Ann. Conf. SE. Ass. Game and Fish Comm. (1969): 553-558. AllSOpp, W. H. L. 1960. The manatee-ecology and use for weed control. Nature. 188: 762. 1969. Aquatic weed control by manatee - its prospects and problems. Pp. 344-351. In Man-Made Lakes. L. E. Obeng (ed.), The Accra Symposium. Ghana Universities Press, Accra. Alm, G. 1959. Connection between maturity, size and age in fishes. Inst. Fresh. Res., Drottningholm, Fish. Bd. Sweden. Report No. 40: 5-145. Almquist, E. 1959. Observations on the effect of rotenone emulsives on fish food organisms. Inst. Fresh. Res., Drottningholm, Fish. Bd. Sweden. Report 40: 146-160. Applegate, R. L., and J. W. Mullan. 1967a. Standing crops of dissolved organic matter, plankton, and seston in a new and an old Ozark Reservoir. Pp. 517-530. In Reservoir Fishery Resources Symposium. Univ. of Georgia, Athens. 226 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 227 Applegate, R. L., and J. W. Mullan. 1967b. Zooplankton standing crops in a new and old Ozark Reservoir. Limno. and Oceanog. 12(4); 592-599. Aronin, E. S., and P. V. Mikheev. 1963. Rehabilitation of the fishery in the shallows of large reservoir. P. 3. In Water levels, fluctuation, and minimum pools in reservoirs for fish and other aquatic resources an annodated bibliography. J. C. Fraser (comp.), FAO Fish. Tech. Pap. No. 113, Rome 1972. Avault, J. W., Jr. 1965. Biological weed control with herbivorous fish. Proc. Souther Weed Conf. 18: 590—1. Axon, J. R. 1971. An evaluation of the trout fishery in Lake Cumberland, Kentucky. Pp. 235—242. In Reservoir Fisheries and Limnology. G. E. Hall (ed.), Am. Fish. Soc., Spec. Publ. No. 8. Backiel, T. 1962. Determination of time of annulus formation of fish scales. ACTA Hydrobiology. Krakow, Poland. 4: 393- 411. Bagenal, T. B. 1967. A short review of fish fecundity. Pp. 89- 111. In The biological basis of freshwater fish production. 8. D. Gerking (ed.), Blackwell Scientific Publications, Oxford and Edinburgh. 1968. Eggs and early life history, part I. Fecundity. Pp. 160-169. In Methods of assessment of fish production in fresh waters. IBP Handbook No. 3. Blackwell Scien- tific Publications, Oxford and Edinburgh. Bailey, N. J. J. 1951. On estimating the Size of mobile popula- tions from recapture data. Biometrika. 38: 293-306. Baker, W. D. 1966. A "Fish Lok" for passing fish through small impoundment structure. Proc. Twentieth Ann. Conf. SE. Ass. Game and Fish Comm. (1966): 457-461. Balon, E. K. 1972. Possible fish stock size assessment and available production survey as developed on Lake Kariba. The African Jour. Tropical Hydrobiology and Fisheries. 2(1): 45-73. Bardach, J. E. 1955. The opercular bone of the yellow perch, Perca fZavescens, as a tool for age and growth studies. Copeia. 2(1955): 107-9. Bauer, 0. N. 1962. The ecology of parasites of freshwater fish. Pp. 3-215. In Parasites of freshwater fish and the biological basis for their control. L. Kochva (trans.), National Science Foundation, Washington, D.C. 23. 24. 25. 26. 27. 28. 29. 30. 31. 32. 33. 34. 35. 228 Becker, D. A., and W. A. Evans. 1967. Fish parasites in new impoundment. Pp. 163-4. In South Central reservoir investigations. T. 0. Duncan (rep.), Prog. Sport Fish Res. 1967. Eur. Sport Fish. & Wildl., Resource Publica- tion 64. , R. G. Heard, and P. D. Holmes. 1966. A pre-impoundment survey of the helminth and copepod parasites of Micropterus app. of Beaver Reservoir in northeast Arkansas. Trans. Am. Fish. Soc. (95(1): 23-34. Beckman, L. G., and J. H. Elrod. 1971. Apparent abundance and distribution of young-of—year fishes in Lake Oahe, 1965-69. Pp. 333-348. In Reservoir Fisheries and Limnology. G. E. Hall (ed.), Am. Fish. Soc. Spec. Publ. No. 8. Bell, G. R., D. V. Libby, and D. T. Lordi. 1970. Phosphorus removal using chemical coagulation and a continuous counter-current filtration process. Fed. Wat. Qual. Adm't., Dept. of the Interior. 57 p. Bell—Cross, G. 1960. Observations on the movement of fish- ladder in northern Rhodesia. Pp. 113-125. In CSA/CTA Third Symp. on Hydrobiology and Inland Fisheries. Bennett, G. W. 1970. Management of lakes and ponds. Second edition. Van Nostrand Reinhold Company. 375 p. Benson, N. G. 1968. Review of fishery studies on Missouri River main stem reservoirs. U. S. Bur. of Sport Fish. & Wildl., Research report 71, 61 p. , and B. C. Cowell. 1967. The environment and plankton density in Missouri River reservoirs. Pp. 358-373. In Reservoir Fishery Resources Symposium. Univ. of Georgia, Athens. Berger, B. L. 1965. Antimycin (Fintrol) as a fish toxicant. Proc. Nineteenth Ann. Conf. SE. Ass. of Game and Fish Comm. (1965): 300-1. Beverton, R. J. H., and S. J. Holt. 1957. On the dynamics of exploited fish populations. Fish. Invest. (II), No. 19. 533 p. Blackburn, R. D., and L. W. Weldon. 1965. A fresh-water snail as a weed control agent. Proc. Southern Weed Conf. 18: 589. . 1970. Control of Hydrilla verticiZZata. Hyacinth Control Jour. 9: 4-9. , D. L. Sutton, and T. Taylor. 1971. Biological control of aquatic weeds. Jour. of the Irrigation and Drainage Division. Proc. Am. Soc. Civil Engr. 97(3): 421-432. 36. 37. 38. 39. 40. 41. 42. 43. 44. 45. 46. 47. 48. 229 Boyd, C. E. 1970. Vascular aquatic plants for mineral nutrient Boyko, removal from polluted waters. Econ. Bot. 24: 95—103. 1971. The limnological role of aquatic macrophytes and their relationship to reservoir management. Pp. 153- 166. In Reservoir Fisheries and Limnology. G. E. Hall (ed.), Am. Fish. Soc. Spec. Publ. No. 8. , and C. P. Goodyear. 1971. Nutritive quality of food in ecological systems. Arch. Hydrobiol., Stuttgart. 69(2): 256-270. E. G. 1950. Age determination in fishes based on examina- tion of finray sections. Prog. Fish-Cult. 12(1): 47-8. Brett, J. R. 1960. Thermal requirements of fish - three decades of study, 1940—1970. Pp. 110-117. In Biological problems in water pollution, 2nd seminar, 1959. Robert A. Taft Sanitary Engineering Center, Tech. Rept. W 60-3. Brezonik, P. L., J. J. Delfino, and G. F. Lee. 1969. Chemistry of N and Mn in Cox Hollow Lake, Wisconsin, following destratification. Jour. Sanit. Engr. Div., ASCE. 95(SA 5): 929-940. Bridges, C. H., and L. S. Hambly. 1971. A summary of eighteen years of salmonid management at Quabbin Reservoir, Massa- chusetts. Pp. 243—254. In Reservoir Fisheries and Limnology. G. E. Hall (ed.), Am. Fish. Soc. Spec. Publ. No. 8. Brooks, N. H., and R. C. Y. Koh. 1969. Selective withdrawal from density-stratified reservoir. ASCE. Jour. Hydraulic Div. 95(HY 4): 1369-1400. Brown, M. E. 1957. Experimental studies on growth. Pp. 361- Brown, 400. In The physiology of fishes, Vol. 1. M. E. Brown (ed.), Academic Press, New York. W. M., III, and J. R. Ritter. 1971. Sediment transport and turbidity in the Eel River basin, California. USGS. Water-supply paper 1986. 67 p. Brylinsky, M., and K. H. Mann. 1973. An analysis of factors governing productivity in lakes and reservoirs. Limno. and Oceanog. 18(1): 1-14. Buck, D. H. 1956. Effects of turbidity on fish and fishing. Trans. North Am. Wildl. Conf. 21: 249-261. Bungenberg de Jong, C. M. 1967. Experiments with diuron in fish ponds of the fish breeding station at Lelystad. Pp. 66-69. In European Weed Research Council, Symposium. 49. 50. 51. 52. 53. 54. 55. 56. 57. 58. 59. 60. 61. 230 Burn, J. W. 1966. Rough fish management. Pp. 492—498. In Inland Fisheries Management. A. Calhoun (ed.), Dept. of Fish and Game, State of California. Burress, R. M. 1961. Fishing pressure and success in areas of flooded standing timber in Bull Shoals Reservoir, Missouri. Proc. Fifteenth Ann. Conf. SE. Ass. Game and Fish Comm., pp. 296-298. , and C. W. Luhning. 1969. Use of antimycin for selective thinning of sunfish populations in ponds. U. S. Bur. Sport Fish & Wildl., Investigations in Fish Control. pp. 1-10. Butler, J. M., F. F. Ferguson, and L. A. Barrios-Duncan. 1968. Significance of animal control of aquatic weeds. Proc. Southern Weed Conf., 21: 304-308. Cady, E. R. 1945. Fish distribution, Norris Reservoir, Tennessee, 1943: 1. Depth distribution of fish in Norris Reservoir. Jour. Tenn. Acad. Sci., 20(1): 103-113. Carlander, K. D. 1955. The standing crop of fish in lakes. Jour. Fish. Res. Bd. Canada, 12(4): 543-570. Carroll, B. B., G. E. Hall, and R. D. Bishop. 1963. Three seasons of rough fish removal at Norris Reservoir, Tennessee. Trans. Am. Fish. Soc., 92(4): 356-364. Carter, E. R. 1957. Investigations and management of the Dewey Lake fishery. Proc. Tenth Ann. Conf. SE. Ass. Game & Fish Comm. (1956): 254-270. Carter, J. P. 1969. Pre- and post-impoundment surveys on Barren River. Kentucky Fish. Bull. No. 50, 33 p. Chalupa, J. 1960. Eutrophication of reservoirs by atmospheric phosphorus. Sci. Pap. Inst. Chem. Tech., Prague, Czecho- slovakia, Fac. Technol. Fuel. Wat. Vol. 4, Pt. 1, pp. 295-308. (English summary) Chapman, G. C. 1951. Some properties of the hypergeometric distribution with applications to zoological sample censuses. Univ. Calif. Publ. Stat., 1: 131-160. 1952. Inverse, multiple and sequential sample censuses. Biometrics, 8: 286-306. Chen, R. L., D. R. Keeney, et a1. 1972. Denitrification and nitrate reduction in Wisconsin lake sediments. Jour. Environ. Quality, 1(2): 158-162. 62. 63. 64. 65. 66. 67. 68. 69. 70. 71. 72. 73. 74. 75. 231 Christensen, L. M., and L. L. Smith. 1965. Characteristics of fish populations in upper Mississippi River backwater areas. Bur. Sport Fish & Wildl., U. S. Dept. of the Interior, Circulation 212, 53 p. Chugunova, N. I. 1963. Age and growth studies in fish. National Science Foundation, Washington, D.C., 131 p. Churchill, M. A. 1958. Effects of impoundments on oxygen resources. Pp. 107-130. In Oxygen relationships in streams. PHS., Robert A. Taft Sanitary Engineering Center, Cincinnati. Claflin, T. O. 1968. Reservoir aufwuchs on inundated trees. Trans. Am. Microsc. Soc., 87(1): 97-104. Clay, C. H. 1960. The Okanagan River flood control project. Pp. 346-351. In the Seventh Tech. Meet. of IUCN, Theme 1, Vol. IV. Athens, Greece. 1961. Design of fishways and other fish facilities. Queens Printer, Ottawa. 301 p. I iJ Clemens, W. A., D.S. Rawson, and J. L. McHugh. 1939. A bio- logical survey of Okanagan Lake, British Columbia. Bull. Fish. Res. Bd. Canada, No. 56, 70 p. Coke, M. 1968. Depth distribution of fish on a bush—cleared area of Lake Kariba, Central Africa. Trans. Am. Fish. Soc., 97(4): 460-465. Coker, R. E. 1954. Streams, lakes, ponds. Univ. North Carolina Press. 328 p. Collins, G. B., and C. H. Elling. 1960. Fishway research at the fisheries-engineering research laboratory. Bur. Comm. Fish., U. S. Dept. of the Interior, Circular 98, 17 p. Cooper, G. P. 1966. Fish production in impoundments. Mich. Dept. Cons. Res. & Devel. Rept., No. 104, pp. 1-12. Cordone, A. J., S. J. Nicola, et a1. 1971. The kokanee salmon in Lake Tahoe. Calif. Fish. & Game. 57(1): 28-43. Cowell, B. C. 1967. The Copepoda and Cladocera of a Missouri River reservoir: A comparison of sampling in the reservoir and the discharge. Limnol. and Oceanog. 12(1): 125-136. , and Hudson. 1967. Some environmental factors influenc- ing benthic invertebrates in two Missouri River reservoirs. Pp. 541-555. In Reservoir Fishery Resources Symposium. Univ. of Georgia, Athens. 76. 77. 78. 79. 80. 81. 82. 83. 84. 85. 86. 87. 88. 232 Craven, R. E., and B. E. Brown. 1969. Benthic micro-invertebrates of Boome Lake, Payne County, Oklahoma. The Southern Naturalist, 14(2): 221-230. Creaser, C. W. 1926. The structure and growth of the scales of fishes in relation to the interpretation of their life- history, with special reference to the sunfish, Eupomotis gibbosus. Univ. Mich., Mus. 2001., Misc. Publ. No. 17, 82 p. 1931. Relative importance of hydrogen-ion concentra- tion, temperature, dissolved oxygen and carbon dioxide tension, on habitat selection by brook trout. Ecology, 11: 246-262. Cross, D. G. 1969. Aquatic weed control using grass carp. Jour. Fish Biology. 1(1): 27-30. Curtis, B. 1960. Observed changes in a river's physical characteristics under substantial reductions in flow due to hydro-electric diversion. Pp. 164-174. In the Seventh Tech. Meet. of IUCN, Theme 1, Vol. IV., Athens, Greece. Cushing, D. H. 1963. The counting of fish with an Echo-sounder. Rapp. et Proces-Verbaux des Reunions, Copenhague, 155: 190-195. Cushing, C. E., and J. R. Olive. 1957. Effects of toxaphene and rotenone upon the macroscopic bottom fauna of two northern Colorado reservoirs. Trans. Am. Fish. Soc., 86: 294-301. Dalrymple, R. L. 1971. Experiences with diuron for aquatic weed control. Proc. Southern Weed Conf., 24: 333-337. Davis, J. T., and J. S. Hughes. 1971. Effects of standing timber on fish populations and fisherman success in Bussey Lake, Louisiana. Pp. 255-264. In Reservoir Fisheries and Limnology. G. E. Hall (ed.), Am. Fish. Soc., Spec. Publ. No. 8. , and H. E. Schafer, Jr. 1964. Water level fluctuation to control aquatic vegetation. Proc. Southern Weed Conf., 17: 328. De Bont, A. F. 1967. Some aspects of age and growth of fish in temperate and tropical waters. Pp. 67-88. In The biological basis of freshwater fish production. 8. D. Gerking (ed.), Blackwell Scientific Publications, Oxford and Edinburgh. De Lury, D. B. 1947. On the estimation of biological populations. Biometrics. 3: 145-167. Deelder, C. L. 1960. Modern fish passes in the Netherlands. Pp. 316-320. In the Seventh Tech. Meet. of IUCN, Theme 1, Vol. IV., Athens, Greece. 89. 90. 91. 92. 93. 94. 95. 96. 97. 98. 99. 100. 233 Dendy, J. S. 1945. Fish distribution, Norris Reservoir, Tennessee, 1943. II. Depth distribution of fish in relation to environmental factors, Norris Reservoir. Jour. Tenn. Acad. Sci., 20(1): 114-134. Denyoh, F. M. K. 1966. Changes in fish population and gear selectivity in the Volta Lake. Pp. 206-219. In Man- Made Lakes. L. E. Obeng (ed.), The Accra Symposium. Ghana Universities Press, Accra. Devaraj, M., and V. Ranganathan. 1967. Incidence of Isoparorchis hyprelobagri (Billet, 1898) (Trematoda, Hemiuridae) among the catfishes of Bhavanisagar Reservoir. Indian Jour. of Fisheries. 14(1-2): 232-250. Dill, W. A., and G. L. Kesteven. 1960. Methods of minimizing the deleterious effects of water- and land-use practices on aquatic resources. Pp. 271-307. In the Seventh Tech. Meet. of IUCN, Theme 1, Vol. IV., Athens, Greece. , and T. V. R. Pillay. 1968. Scientific basis for the conservation of non-oceanic living aquatic resources. FAO Fish. Tech. Pap. No. 82, 15 p. Rome. Doudoroff, P., and M. Katz. 1950. Critical review of literature on the toxicity of industrial wastes and their components to fish - 1. Alkalis, acids and inorganic gases. Sewage Ind. Wastes. 22: 1432-1458. Drachev, S. M., K. R. Amrin, and A. A. Rylinkina. 1966. The influence of evaporation depressants on the quality of water and its biochemical processes. Pp. 97-104. In Production and circulation of organic matter in inland waters. M. Yariv (Trans.), National Science Foundation, Washington, D.C. Dzyuban, N. A. 1957. The formation of zooplankton in reservoirs. Pp. 641-647. In Trans. Sixth Conf. on the Biol. of Inland Waters. M. Raveh (trans.), National Science Foundation, Washington, D .C. Eden, G. E. 1965. The measurement of turbidity in water. Jour. IL? Water Treatment and Examination. 14(part 1): 27-44. Eicher, G. J. 1970. Fish passage. Pp. 163-171. In A century of fisheries in North America. N. G. Benson (ed.), Am. Fish. Soc., Spec. Publ. No. 7. E. I. F. A. C. 1969. Water quality criteria for European freshwater fish - extreme pH values and inland fisheries. Water Research. 3(8): 593-612. 1969. Water quality criteria for European freshwater fish - water temperature and inland fisheries. Water Research. 3(9): 645-662. 101. 102. 103. 104. 105. 106. 107. 108. 109. 110. 111. 112. 113. 234 Eley, R. L., N. E. Carter, and T. C. Dorris. 1967. Physica- chemical limnology and related fish distribution of Keystone Reservoir. Pp. 333—357. In Reservoir Fishery Resources Symposium. Univ. of Georgia, Athens. Ellis, M. M. 1937. Some fishery problems in impounded waters. Trans. Am. Fish. Soc., 66(1936): 63-75. 1942. Fresh-water impoundments. Trans. Am. Fish. Soc., 71(1941): 80-93. 1967. Detection and measurement of stream pollution. Pp. 129-185. In The biology of water pollution. L. E. Keup, et a1. (comp.), Fed. Wat. Poll. Contr. Adm't., Dept. of the Interior, Cincinnati. Elser, H. J. 1955. An epizootic of ichthyophthiriasis among fish in a large reservoir. Prog. Fish-Cult., 17(3): 132-3. Engelbrecht, R. S., J. T. O'Connor, and M. Ghosh. 1965. Sig- nificance and removal of iron in water supplies. Pp. 8- 24. In Proc. 4th Ann. Sanit. and Water Res. Engr. Conf., Nashville, Tennessee. Eren, Y., A. Yashouv, and Y. Langer. 1972. Effect of fish on the bottom of reservoirs. Bamidgeh. 24(2): 40-48. Ergens, R. 1966. Results of parasitological investigations on the health of Bear Zucius L., in the Lipno Reservoir. Folia Parasit., Praha. 13(3): 222-236. Fetterrolf, C. M., Jr. 1957. Stocking as a management tool in Tennessee reservoirs. Proc. 10th Ann. Conf. SE. Ass. Game 8 Fish Comm. (1956): 275-279. Fillion, D. B. 1967. The abundance and distribution of benthic fauna of three mountain reservoir on the Kananskis River in Alberta. Jour. Appl. Ecol., 4(1): l-ll. Findenegg, I. 1969. Factors controlling primary productivity, especially with regard to water replenishment, stratifica- tion, and mixing. Pp. 107-119. In Primary productivity in aquatic environments. C. R. Goldman (ed.), Univ. of Calif. Press, Berkeley and Los Angeles. Fitz, R. B. 1968. Fish habitat and population changes resulting from impoundment of Clinch River by Melton Hill Dam. Jour. Tenn. Acad. Sci., 43(1): 7-15. Fitzgerald, G. P. 1971. Aerobic lake muds for the removal of phosphorus from lake waters. Pp. 25—37. In Nutrient sources for algae and their control. Environmental Protection Agency. WPCRS. No. 16010 EHR. 114. 115. 116. 117. 118. 119. 120. 121. 122. 123. 124. 125. 126. 235 Frantz, T. C., and A. J. Cordone. 1970. Food of lake trout in Lake Tahoe. Calif. Fish and Game, 56(1): 21-35. Fraser, J. C. 1972. Water levels, fluctuation, and minimum pools in reservoirs for fish and other aquatic resources. An annotated bibliography. FAO Fish. Tech. Pap. No. 113, Rome. Frenkiel, J. 1965. Evaporation reduction, physical and chemical principles and review of experiments. UNESCO. 79 p. Frey, D. G. 1967. Reservoir research - objectives and prac- tices with an example from the Soviet Union. Pp. 26-36. In Reservoir Fishery Resources Symposium, Univ. of Georgia, Athens. Frizzell, J. L. 1962. Hydrothol for control of aquatic weeds. Hyacinth Control Jour., l: 14. Fryer, J. D., and R. J. Makepeace (ed.). 1970. Weed control handbook, Vol. II. Recommendations. Sixth Edition. Blackwell Scientific Publications, Oxford and Edinburgh. 331 p. Fuerst, M. 1970. Experiments on the transplantation of new fish-food organisms into Swedish impounded lakes. P. 13. In Water levels, fluctuation, and minimum pools in reser- voirs for fish and other aquatic resources. An annotated bibliography. FAO Fish. Tech. Pap. No. 113, Rome. Funk, W, H., and A. R. Gaufin. 1971. Phytoplankton productivity in a Wyoming Cooling-Water reservoir. Pp..l67-l78. In Reservoir Fisheries and Limnology. G. E. Hall (ed.), Am. Fish. Soc., Spec. Publ. No. 8. Gabrielson, I. N. (ed). 1950. The fisherman's encyclopedia. Stackpole and Heck, New York. 698 p. Gallagher, J. E. 1962. Water hyacinth control with amitrol-T. Hyacinth Control Jour., 1: 17-18. Gasaway, C. R. 1970. Changes in the fish population in Lake Francis Case in South Dakota in the first 16 years of impoundment. U. 8. Fish and Wildl. Service, Tech. Pap. No. 56. Gerloff, G. C., and F. Skoog. 1957. Nitrogen as a limiting factor for the growth of Microcystis aeruginosa in southern Wisconsin lakes. Ecol., 38: 556-561. Gianelli, W. R. 1971. Removal of nitrate by an algal system. Calif. Dept. Wat. Res., Wat. Poll. Contr. Res. Series. 132 p. 127. 128. 129. 130. 131. 132. 133. 134. 135. 136. 137. 138. 139. 236 Goering, J. J. 1972. The rate of nitrogen in eutrophic.processes. Pp. 43-68. In Water pollution microbiology. R. Mitchell (ed.), Wiley-Interscience. New York. Goldman, J. C., D. B. Porcella, et a1. 1972. Review paper: The effect of carbon an algae growth; its relationship to eutrophication. Water Research. 6(6): 637-680. Gottschalk, L. C. 1948. Analysis and use of reservoir sedimen- tation data. Pp. 131-138. In Proc. of the Federal Inter-Agency Sedimentation Conference. Bur. Reclamation, U. 8. Dept. of the Interior, Washington, D.C. Gould, H. R. 1960. Turbidity currents. Pp. 201-207. In Compre- F1 hensive survey of sedimentation in Lake Mead, 1948-49. i USGS. Prof. Pap. 295. i 1960. Sedimentation in relation to reservoir utiliza- tion. Pp. 215-229. In Comprehensive survey of sedimenta- _ tion in Lake Mead, 1948-49. USGS. Prof. Pap. 295. -J Govind, B. V. 1963. Preliminary studies on plankton of the Tungabhadra Reservoir. Indian Jour. of Fisheries. 10(Sec A): 148-158. Grimal'skii, V. D. 1957. The zooplankton of the Dniester and its changes in conditions of the Dubossary Reservoir. Pp. 385-391. In Trans. Sixth Conf. on the Biol. of inland waters. M. Raveh (trans), National Science Foundation, Washington, D.C. Grimas, U. 1961. The bottom fauna of natural and impounded lakes in northern Sweden. Inst. Freshwater Res., Fish. Bd. Sweden. Rept. No. 42, pp. 183-237. F] Grinstead, B. G. 1971. Reproduction and some aspects of the . early life history of walleye, Stizostedion vitreum (Mitchell) in Canton Reservoir, Oklahoma. Pp. 41-51. I In Reservoir Fisheries and Limnology. G. E. Hall (ed.), Am. Fish. Soc., Spec. Publ. No. 8. Grizzell, R. A., Jr., and W. W. Neely. 1962. Biological control &3 for waterweeds. Trans. North America Wildlife Conf., 27: 107-113. Gulin, V. V. 1968. Some aspects of the procedure for determining the relative age composition of a commercial fish stock in inland waters. Jour. of Ichthyology. 8(1): 107-118. Hanson, W. D. 1962. Dynamics of the largemouth bass population in Bull Shoals Reservoir, Missouri. Proc. 16th Ann. Conf. SE. Ass. Game and Fish Comm., pp. 398-404. Harbeck, G. E., Jr. 1958. Results of energy-budget and mass- transfer computations. Pp. 35-38. In Water-loss investi- gations; Lake Mead studies. USGS. Prof. Pap. 298. 140. 141. 142. 143. 144. 145. 146. 147. 148. 149. 150. 151. 152. 237 Harding, D. 1966. Lake Kariba. The hydrology and development of fisheries. Pp. 7—18. In Man-Made Lakes. R. H. Lowe- McConnell (ed.), Academic Press, New York. Harrison, A. D. 1956. The effects of sulfuric acid pollution and the biology of streams in the Transvaal, South Africa. Verh. Int. Verein. theor. angew. Limnology. 13: 603-610. Hartman, R. T., and J. E. Graffins. 1960. Quantitative seasonal changes in the.phytoplankton communities of Pymatuning Reservoir. Ecol., 41(2): 333—340. Hounam, C. E. 1963. The temporal and spatial distribution of evaporation in Australia. Water Resource use and manage- ment. Pp. 102-111. Hawkes, R. B. 1965. Domestic phases of program designed to use insects to suppress alligatorweed. Proc. Southern Weed Conf., 18: 584-585. Hawkes, H. A. 1969. Ecological changes of applied significance induced by the discharge of heated waters. Pp. 15-57. In Engineering aspects of thermal pollution. F. L. Parker and P. A. Krenkel (ed.), Vanderbilt Univ. Press. Hayes, F. R., and E. H. Anthony. 1964. Productive capacity of North American lakes as related to quantity and trophic level of fish, the lake dimensions and the water chemistry. Trans. Am. Fish. Soc., 93(1): 53-57. Hayne, D. W., G. E. Hall, and H. M. Nichols. 1967. An evalua- tion of cove sampling of fish populations in Douglas Reservoir, Tennessee. Pp. 244-297. In Reservoir Fishery Resources Symposium. Univ. of Georgia, Athens. Heinemann, H. G., and V. I. Dvorak. 1963. Improved volumetric :] survey and computation procedures for small reservoirs. - WW Pp. 845-856. In Proc. of the Federal Inter-Agency Sedi— ‘ mentation Conference 1963. USDA, ARS Misc. Publ., No. 1 970. , i Hem, J. D. 1970. Study and interpretation of the chemical Hg characteristics of natural water. Second edition. USGS. ‘ Water-supply paper 1473. 363 p. Henley, J. P. 1966. Evaluation of rotenone sampling with SCUBA gear. Proc. 20th Ann. Conf. SE. Ass. Game and Fish Comm., pp. 439-445. Hickling, C. F. 1961. Tropical inland fisheries. Longmans, London, 287 p. Hile, R. 1970. Body-scale relation and calculation of growth in fishes. Trans. Am. Fish. Soc., 99(3): 468-474. 153. 154. 155. 156. 157. 158. 159. 160. 161. 162. 163. 164. 238 Hiltibran, R. C. 1970. Algae control in Illinois. Proc. North Central Weed Control Conf., 25: 92-3. Hoffman, G. L., and 0. N. Bauer. 1971. Fish parasitology in water reservoir: A review. Pp- 495-511. In Reservoir Fisheries and Limnology. G. E. Hall (ed.), Am. Fish. Soc., Spec. Publ. No. 8. Hora, S. L., and T. V. R. Pilay. 1962. Handbook on fish culture in the Indo-Pacific region. FAD Fish. Biol. Tech. Pap. No. 14, 203 p. Rome. Horak, D. L., and H. A. Tanner. 1964. The use of vertical gill— nets in studying fish depth distribution, Horsetooth Reservoir, Colorado. Trans. Am. Fish. Soc., 93(2): 137- 145. v. Hourston, W. R., and D. MacKinnon. 1957. Use of an artificial spawning channel by salmon. Trans. Am. Fish. Soc., 86 ' (1956): 220-230. S} a; Houser, A., and H. E. Bryant. 1967. Sampling reservoir fish populations using midwater trawls. Pp. 391-404. In Reservoir Fishery Resources Symposium. Univ. of Georgia, Athens. , and J. E. Dunn. 1967. Estimating the size of the thread- fin shad population in Bull Shoals Reservoir from mid- water trawl catches. Trans. Am. Fish. Soc., 96(2): 176-184. Hruska, V. 1965. The changes of benthos in Slappy Reservoir after establishing Orlik Reservoir and their influence upon the fish stock. Verh. Int. Verein. theor. angew. Limnol. 16(2): 741-746. fa Hull, C. H. J. 1965. Photosynthesis as a factor in the oxygen a balance of reservoirs. Pp. 77-90. In Symposium on E streamflow regulation for quality control. Robert A. “ Taft Sanit. Engr. Center, Cincinnati, PHS Publ. No. 999-WB- 30 . £9 Hulsey, A. H. 1957. Effects of a fall and winter drawdown on a flood control lake. Proc. 10th Ann. Conf. SE. Ass. Game and Fish Comm. (1956): 285-289. 1959. A proposal for the management of reservoirs for fisheries. Proc. 12th Ann. Conf. SE. Ass. Game and Fish Comm. (1958): 132-143. Hunt, P. C., and J. W. Jones. 1972. The effect of water level fluctuations on a littoral fauna. Jour. Fish. Biol. 4(3): 385-394. 239 165. Hutchinson, G. E. 1957. A treatise on limnology. Volume 1. Geography, physics, and chemistry. John Wiley & Sons, Inc., New York. 1015 p. 166. Il'ina, L. K., and N. A. Gordeyev. 1970. Dynamics of the repro- ductive conditions of phytOphylous fishes at different stages in reservoir formation. Jour. of Ichthyology. 10(3): 282-285. 167. Ingols, R. S., and R. D. Wilroy. 1962. Observations on manganese in Georgia waters. Jour. Am. Wat. Wks. Ass., 54(2): 203-207. 168. . 1963. Mechanism of manganese solution in lake waters. . Jour. Am. Wat. Wks. Ass., 55: 282-290. FE 169. Ioffe, Ts. I. 1972. The improvement of reservoir productivity through acclimatization of invertebrates. Verh. Int. Verein. theor. angew. Limnol. 18: 818-821. 170. Irwin, W. H. 1957. The management of large impoundments for 3 . fish production. Proc. 10th Ann. Conf. SE. Ass. Game and Fish Comm. (1956): 271-275. 171. , J. M. Symons, and G. G. Robeck. 1967. Water quality in impoundments and modifications from destratification. Pp. 130-152. In Reservoir Fishery Resources Symposium. Univ. of Georgia, Athens. 172. . 1969. Impoundment destratification by mechanical pump- ing. Pp. 251-274. In Water quality behavior in reservoirs. J. M. Symons (cop1.), PHS Publ. No. 1930. 173. Iskov, M. P., and V. P. Koval. 1965. Parasite fauna of the fish of the Kakhovskoe Reservoir 8 years after its filling with water. Biol. Abst., 48(24): #124585, 1967. 174. Isom, B. G. 1971. Effects of storage and mainstream reservoir on benthic macroinvertebrates in the Tennessee Valley. Pp. 179-191. In Reservoir Fisheries and Limnology. G. E. Hall (ed.), Am. Fish. Soc., Spec. Publ. No. 8. 175. Ivanov, M. V. 1957. Assessment of sulfur cycle processes in lakes using radioactive sulfur. Pp. 160-166. In Trans. Sixth Conf. on the Biol. of Inland Waters. M. Raveh (trans.), U. 8. Dept. of Commerce, Washington, D.C. 176. . 1964. Contemporary production of hydrogen sulfide and sulfur in reservoirs and the role of micro-organisms in these processes. Pp. 123-145. In Microbiological processes in the formation of sulfur deposits. 8. Nemchonok (trans.), The National Science Foundation, Washington, D.C. 177. Izyumova, N. A. 1964. The formation of the parasitofauna of fishes in the Ribinsk Reservoir. Pp. 49-55. In Parasitic worms and aquatic conditions. Czechoslovakia Acad. Sci., Prague, 1962. - 178. 179. 180. 181. 182. 183. 184. 185. 186. 187. 188. 189. 190. Jennings, R4 C. 1967. The commercial use of diquat in the ’ T! 240 Jackson, P. B. N. 1960. On the desirability or otherwise of introducing fishes to waters that are foreign to them. Third Symposium on Hydrobiol. and Inland Fisheries problems of major lakes. CCTA Publ. No. 63, pp. 157-164. 1966. The establishment of fisheries in manrmade lakes in the tropics. Pp. 53-69. In Man-Made Lakes. R. H. Lowe—McConnell (ed.), Academic Press, London. Jenkins, R. M. 1961. Reservoir fish management - progress and challenge. Sport Fishing Institute Spec. Publ., Washington, D.C., 22 p. . 1964. Reservoir fishery research strategy and tactics. Bur. of Sport Fish. & Wildl., U. S. Dept. of the Interior, Circular 196, 12 p. ‘saalfi 1967. The influence of some environmental factors on standing crop and harvest of fish in U. S. reservoirs. Pp. 289-321. In Reservoir Fishery Resources Sympsoium, Univ. of Georgia, Athens. .‘-._._ _..__- ”.— h 'r. v V 1970a. The influence of engineering design and opera— tion and other environmental factors on reservoirs fishery resources. Wat. Res. Bull., 6(1): 110-119. 1970b. Reservoir fish management. Pp. 173-182. In A century of fisheries in North.America. N. G. Benson (ed.), Am. Fish. Soc., Spec. Publ. No. 7. . 1970c. National reservoir research program. Prog. in Sport Fish. Res. 1970, Fish and Wildl. Service, Resource Publ. 106, p. 264. United Kingdom for the control of submerged water weeds. ' 1 Pp. 109-110. In Symposium European Weed Research Council. d Jeppson, P. W. 1957. The control of squawfish by use of dynamite, I spot treatment and reduction of lake levels. Prog. Fish— 5 3 Cult., 19(4): 168-171. L3 Jester, D. B. 1971. Effects of commercial fishing species introductions, and drawdownal control on fish populations in Elephant Butte Reservoir, New Mexico. Pp. 265-285. In Reservoir Fisheries and Limnology. G. E. Hall (ed.), Am. Fish. Soc., Spec. Publ. No. 8. Jones, J. R. E. 1948. A further study of the reactions of fish to toxic solutions. Jour. Exp. Biol., 25: 22-34. Juday, C., E. A. Birge, et a1. 1927. Phosphorus content of lake waters of northeastern Wisconsin. Trans. Wisc. Acad. Sci. Arts and Letters, 23:.233—248. 191. 192. 193. 194. 195. 196. 197. 198. 199. 200. 201. 202. 203. 204. 241 Kabanov, K. M. 1961. Macrophytes and plankton of controlled water bodies. Biol. Abstr., 41(6): #21511, 1963. Kalashnikova, E. P., and Y. I. Sorokin. 1966. Primary produc- tion of phytoplankton photosynthesis in the Bratsk Reservoir. Pp. 185-193. In Production and circulation.of organic matter in inland waters. M. Yariv (trans.), The National Science Foundation, Washington, D.C. Keith, W. E. 1970. Preliminary results in the use of a nursery pond as a tool in fishery management. Proc. 23rd Ann. Conf. SE. Ass. Game and Fish Comm., (1969): 501-511. Kerr, P. C., D. F. Paris, and D. L. Brockway. 1970. The inter- relation of carbon.and phosphorus in regulating heterotrophic and autotrophic populations in aquatic ecosystems. Wat. Poll. Contr. Res. Ser., 16050 FGS. Keup, L. E. 1968. Phosphorus in flowing waters. Water Research. 2(5): 373-386. Khan, A. A., and A. Q. Siddique. 1971. Primary production in a tropical fish pond at Aligarh, India. Hydrobiologia, 37 (3_4): 447'456. Khoroshko, P. N., and A. D. Vlasenko. 1970. Artificial spawning grounds of sturgeon. Jour. of Ichthyology. 10(3): 286-292. Kim, W. S., and K. Roberson. 1968. On the use of otoliths of sockeye salmon for age determination. Univ. of Washington Publ. in Fisheries, New Series 111: 149-168. Kimsey, J. B. 1958. Fisheries problems in impounded waters of California and the Lower Colorado River. Trans. Am. Fish. SOCo, 87(1957): 319-3320 King, D. L. 1970. The role of carbon in eutrophication. Jour. Wat. Poll. Contr. Fed., 42: 2035-2051. Kiser, R. W., J. R. Donaldson, and P. R. Olson. 1963. The effect of rotenone on zooplankton populations in freshwater lakes. Trans. Am. Fish. Soc., 92(1): 17-24. Kittrell, F. W. 1958. Effects of impoundments on dissolved oxygen resources. Sewage and Industrial Wastes. 31(9): 1065-1078. . 1965. Thermal stratification in reservoirs. Pp. 56- 67. In Symposium on streamflow regulation for quality control. Robert A. Taft Sanit. Engr. Center, Cincinnati. PHS Publ. No. 999-WP-30. Klein, W. D. 1967. Evaluation of a pulsating direct—current shocking device for obtaining trout from a lake for‘popu- lation estimates. Prog. Fish—Cult. 29(3): 140-149. 205. 206. 207. 208. 209. 210. 211. 212. 213. 214. 215. 216. 217. 242 Knight, W. E. 1965. Improvement of the quality of reservoir discharges through control of discharge elevation. Pp. 279-290. In Symposium on streamflow regulation for quality control. Robert A. Taft Sanit. Engr. Center, Cincinnati. PHS Publ. No. 999-WP-30. Kochsiek, K. A., J. L. Wilhm, and R. Morrison. 1971. Species diversity of net zooplankton and physicochemical conditions in Keystone Reservoir, Oklahoma. Ecology 52(6): 1119-1125. Krishnamurthy, K. N. 1966. Preliminary studies on the bottom macrofauna of the Tungabhadra Reservoir. Proc. Indian Acad. Sci. 63(2): 96-103. Kryzanek, E. 1970. Formation of bottom fauna in the Goczalkowice dam reservoir. ACTA Hydrobiol., Krakow 12(4): 399-421. Kuentzel, L. E. 1969. Bacteria, carbon dioxide, and algal blooms. Jour. Wat. Poll. Contr. Fed. 41: 1737-1747. Kuznetsov, V. A. 1971. The effect of regulation of the dis- charge of the Volga on the reproduction of asp, zope, white bream and bleak in Sviyaga Bay, Kuybyshev Reservoir. Jour. of Ichthyo. 11(2): 186-192. Lagler, K. F. 1952. Freshwater fishery biology. wm. C. Brown Company, Dubuque, Iowa. 421 p. . 1971. Ecological effects of hydroelectric dams. Pp. 133—157. In Power generation and environmental changes. D. A. Berkowitz and A. M. Squires (ed.), The MIT Press, Massachusetts. Lake Tahoe Area Council. 1971. Eutrophication of surface waters - Lake Tahoe Indian Creek Reservoir. Environmental Pro- tection Agency. No. 16010 Dny, 16010 DSW. Lakshminarayana, S. S. 1965. Studies on the phytoplankton of the River Ganges, Varanasi, India, Part II. The seasonal growth and succession of the plankton algae in the River Ganges. Hydrobiologia, 25: 138-165. Lange, W. 1967. Effect of carbohydrates on the symbiotic growth of planktonic blue-green algae with bacteria. Nature, London, 215: 1277-78. Lantz, K. E., T. Davis, et a1. 1964. Water level fluctuation - its effects on vegetation control and fish populations management. Proc. 18th Ann. Conf. SE. Ass. Game and Fish Comm. PP. 483-494. Le Cren, E. D. 1958. Some observations on methods of speeding up fish population assessments. Pp. 97-104. In A symposium on some problems for biological fishery survey and tech- niques for their solution. Inter. Comm. Northwest Atlantic Fisheries. Spec. Publ. No. 1. 218. 219. 220. 221. 222. 223. 224. 225. 226. 227. 228. 229. 230. 243 . 1965. Some factors regulating the size of populations of freshwater fish. Mitt. Inter. nat. Verein. Limnol. Stuttgart 13: 88-105. . 1972. Fish production in freshwaters. Pp. 115-133. In Conservation and productivity of.natural waters. R. W. Edwards and D. J. Garrod (ed.), Symp. 2001. Soc. London (1972) No. 29. Lee, G. F., and A. W. Hoadley. 1967. Biological activity in relation to the chemical equilibrium composition of natural waters. Pp. 319-338. In Equilibrium concepts in natural water systems. R. F. Gould (ed.), Adv. in Chem. Series 67. Lennon, R. E. 1966. Antimycin - a new fishery tool. Wisc. Cons. Bull. 31(2): 4-5. , and B. L. Berger. 1970. A.resume on field applications of antimycin A to control fish. U.S. Bur. Sport Fish & Wildl., Invest. in Fish Contr. 40: 1-19. Leonard, E. M., and K. E. Sneed. 1951. Instrument to cut cat- fish spines for.age and growth determinations. Prog. Fish-Cult. 13(4): 232. Leslie, P. H., and D. H. S. Davis. 1939. An attempt to determine the absolute number of rats on a given area. Jour. Animal Ecol. 8: 94-113. Lewis, S. A. 1970. Age and growth of walleye, Stizostedion vitreum vitreum (Mitchill), in Canton Reservoir, Oklahoma. Okla. Acad. Sci. Proc. 50:84-86. Lindgren, P. E. 1960. About the effect of rotenone upon ben- f} thonic animals in lakes. Inst. of Freshwater Res., fror Drottningholm, Fish. Bd. Sweden, Rept. No. 41: 172-184. ” Linn, J. D., and T. C. Frantz. 1965. Introduction of the opossum shrimp (Mysis relicta Loven) into California and _ Nevada. Calif. Fish and Game 51(1): 48-51. 3 L Little, E. C. S. 1969. Weeds and man-made lakes. Pp. 284-291. In Man-Made Lakes. L. E. Obeng (ed.), The Accra Symposium. Ghana Universities Press, Accra. Livermore, D. F., and W. E. wunderlich. 1970. Mechanical removal of organic production from waterways. Pp. 494-519. In Eutrophication: causes, consequences, correctives. National Academy of Sciences, Washington, D.C. McCarraher, D. B., M. L. Madsen, and R. E. Thomas. 1971. Ecology and fishery management of McConaughy Reservoir, Nebraska. Pp. 299-311. In Reservoir Fisheries and Limnology. G. E. Hall (ed.), Am. Fish. Soc., Spec. Publ. No. 8. 231. 232. 233. 234. 235. 236. 237. 238. 239. 240. 241. 242. 243. 244 McCombie, A. M. 1953. Factors influencing the growth of phyto- plankton. Jour. Fish. Res. Bd. Canada 10(5): 254-280. McEwen, G. F. 1941. Observations on temperature, hydrogen-ion concentration, and period of stagnation and overturning in lakes and reservoirs of San Diego County, California. Univ. of Calif., Scripps Inst. of Ocean. Bull. 4(9): 219-259. McLachlan, A. J. 1969. The effect of aquatic macrOphytes on the variety and abundance of benthic fauna in a newly created lake in the tropics (Lake Kariba). Arch. Hydrobiol. 66(2): 212-231. r? , and S. M. McLachlan. 1971. Benthic fauna and sediments . ..... in the newly created Lake Kariba (Central Africa). Ecol. . 52(5): 800-809. Maar, A. 1960. Dams and drawn-out stream fisheries in y southern Rhodesia. Pp. 139-151. In the Seventh Tech. p- Meet. of IUCN, Theme 1, Vol. IV. Athens, Greece. ' Mackenthun, K. M. 1969. The practice of water pollution biology. Tech. Support, Fed. Wat. P011. Contr. Adm't., U. S. Dept. of the Interior. 281 p. , and Ingram. 1967. Biological associated problems in freshwater environments: Their identification, investiga- tion and control. Fed. Wat. Poll. Contr. Adm't., U. S. Dept. of the Interior. 287 p. , and R. Porges. 1964. Limnological aspects of recrea- tional lakes. U. 8. Dept. of Health, Education and Welfare. PHS Publ. No. 1167, 176 p. Mackenzie, J. W., and L. Hall. 1967. Elodea control in south- *- east Florida with diquat. Hyacinth Control Jour. 6: 37-44. Maddock, T. L., Jr. 1960. The sediment problem in reservoir. Pp. 245-248. In Comprehensive survey of sedimentation in Lake Mead, 1948-49. USGS Prof. Pap. 295. Manges, D. E. 1950. Fish tagging studies in TVA storage reservoirs, 1947-1949. Jour. Tenn. Acad. Sci. 25(2): 126-140. Mansfield, W. W. 1963. Control of evaporation. Pp. 112-115. In Proc. of Symp. on Water Resources use and Management, Canberra, Australia. Margin, G. B., Jr., and L. E. Randall. 1960. Review of litera- ture on evaporation suppression. USGS Prof. Pap. 272-C. 17 p. 245 244. Markofsky, M., and D. R. F. Harleman. 1971. A predictive model for thermal stratification and water quality in reservoirs. Wat. Qual. Off., Environ. Prot. Agen., Res. Grant No. 16130 DJH. 283 p. 245. Martin, R. 0. R., and R. L. Hanson. 1966. Reservoirs in the United States. USGS Wat.-Supp. Pap. 1838, 115 p. 246. Marzolf, R. C. 1955. Use of pectoral spines and vertebrae for determining age and.growth of the channel catfish. Jour. Wildl. Management 19(2): 243-249. 247. Mathis, W., and A. Hulsey. 1960. Rough fish removal from Lake Caterina, Arkansas- Proc. 13th Ann. Conf. SE. Ass. Game and Fish Comm. (1959): 197-202. 248. May, A. W. 1967. Otolith age validation in Labrador cod. Fish. Res. Bd. Canada pp. 151-155. 249. Mechalas, B. J., P. M. Allen, III, and W. W. Matyskiela. 1970. A study of nitrification and denitrification. Fed. Wat. Qual. Adm't., U. S. Dept. of the Interior. 90 p. 250. Meehean, O. L. 1960. Multiple purpose planning for aquatic resources. Pp. 53-60. In the Seventh Tech. Meet. of IUCN, Theme 1, Vol. IV. Athens, Greece. 251. Meyers, J. S. 1962. Evaporation from the 17 western states. USGS Pof. Pap. No. 272-D. 252. Michael, R. G. 1968. Studies on the bottom fauna.in.a tropical freshwater fish pond- Hydrobiologia 31(2): 203-230. charged from a multiple-purpose reservoir. Pp. 37-41. In Reservoir Fishery Resources Symposium. Univ. of Georgia, Athens. 253. Middleton, J. B. 1967.. Control of temperatures of water dis- :3 254. Mihursky, J. A., and V. S. Kennedy. 1967. Water temperature criteria to protect aquatic life - A summary. Pp. 20- 32. In Symp. on Wat. Qual. Criteria to protect aquatic life. E. L. Cooper (ed.), Am. Fish. Soc., Spec. Publ. No. 4. '1‘ 'I." .rg-r‘ur i‘-' all- \ ‘k‘j‘ '- ‘4; 255. Miroschnichenko, M. P. 1971. Chironomid larvae of the Tsimlyanskoye Reservoir. Limnologica (Berlin) 8(1): 107-109. 256. Misra, G., and N. Das. 1969. Studies on the control of water- hyacinth. 1. Response of water hyacinth to two hormone herbicides, 2,4-D and 2,4,5-T. Hyacinth Control Jour. 8:,22-3. \ 257. Mleczko, A. 1968. The vertical distribution of zooplankton in the Goczalkowice Reservoir in the year 1957-1959. ACTA Hydrobiol. (Poland) 10(3): 373-393. 258. 259. 260. 261. 262. 263. 264. 265. 266. 267. 268. 269. 270. 271. 246 Montgomery, A. B. 1965. The need for aquatic weed research from the standpoint of fish-production, harvesting and toxicity. Proc. Southern Weed Conf. 18: 482-3. Moore, J. G. 1968. Water quality criteria. Fed. Wat. Poll. Contr. Adm't., U. S. Dept. of the Interior. 234 p. Mortimer, C. H. 1971. Chemical exchanges between sediments and water in the Great Lakes - speculations on probable regula- tory mechanisms. Limno. & Oceanogr. 16(2): 387-404. Morton, S. D., P. H. Derse, and R. C. Sernau. 1971. The carbon dioxide system and eutrophication. Office of Research and Monitoring, Environ. Protection Agency, Grant 16010 DXV. Mount, D. I. 1966. The effect of total hardness and pH on the acute toxicity of zinc to fish. Int. Jour. Air Water Poll. 10: 49-56. Mulligan, H. F. 1969. Management of aquatic vascular plants and algae. Pp. 464-482. In Eutrophication: causes, consequences, correctives. National Academy of Sciences, Washington, D.C. Myers, H. C. 1961. Manganese deposits in western reservoirs and distribution systems. Jour. Am. Wat. Wks. Ass. 53(5): 579-588. Neel, J. K. 1967. Reservoir eutrophication and dystrophication following impoundment. Pp. 322-332. In Reservoir Fishery Resources Symposium. Univ. of Georgia, Athens. Neess, J. C. 1949. Development and status of pond fertilization in Central Europe. Trans. Am. Fish. Soc. 76: 335—358. Netsch, N. F., G. M. Kersh, Jr., et a1. 1971. Distribution of young gizzard and threadfin shad in Beaver Reservoir. Pp. 95-105. In Reservoir Fisheries and Limnology. G. E. Hall (ed.), Am. Fish. Soc., Spec. Publ. No. 8. Newman, J. F. 1967. The ecological effects of bipyridyl herbi- cides for aquatic weed control. A symposium, European Weed Research Council, pp. 168-174. Nezhivenko, F. 1969. The creation of spawning fields in reservoirs. Sport Fisheries Abstract 15(1): 74, #11794. Nikolskii, G. V. 1969. Theory of fish population dynamics, as the biological background for rational exploitation and management of fishery resources. J. E. S. Bradley (trans- lated from Russian). Oliver and Boyd, Edinburgh. 323 p. Nikolsky, G. V. 1963. The ecology of fishes. L. Birkett (translated from Russian), Academic Press, New York. 352 p. "9' h 111‘ 272. 273. 274. 275. 276. 277. 278. 279. 280. 281. 282. 283. 247 Northcote, T. G. 1970. Advances in management of fish in natural lakes of Western North America. Pp. 129-139. In A century of fisheries in North America. N. G. Benson (ed.), Am. Fish. Soc., Spec. Publ. No. 7. Oborn, E. T. 1962. A survey of pertinent biochemical literature. USGS Water-Supply Paper 1459-F, pp. 11-190. , and J. D. Hem. 1962. Some effects of the larger types of aquatic vegetation on iron content of water. USGS Water-Supply Paper l459-I, pp. 237-268. Odum, E. P. 1959. Fundamentals of ecology. 2nd edition. W. B. Saunders Company, Philadelphia. 546 p. Olsen, A. M. 1954. The biology, migration, and growth rate of the school shark (Galeorhinus australis Macleay) (Carcharhani- dae) in south-eastern Australian waters. Aust. Jour. mar. Freshwat. Res. 5: 353-410. Ordal, E. J., and R. E. Pacha. 1963. The effects of temperature on disease in fish. Pp. 39-56. In Water temperature influences effects, and control. Fed. wat. Poll. Contr. Adm't., U. 8. Dept. of the Interior. 160 p. Ostroumov, A. A. 1957. The composition of fish stocks in the Uglich and Ivan'kovo reservoirs. Pp. 305-311. In Trans. Sixth Conf. Biol. of Inland Waters. M. Raveh (trans. from Russian), The National Science Foundation, Washington, D.C. Pais-Cuddou, I. C. dos M., and S. N. C. Rawal. 1969. Sedimenta- tion of reservoirs. ASCE Irrigation and Drainage Division, Jour. 95(3): 415-429. Paperna, I. 1968. Ectoparasitic infections in fish of the Volta Lake, Ghana. Bull. Wildl. Disease Ass. 4(4): 135- 137. Parrish, B. B. 1958. Some notes on methods used in fishery research. Pp. 151-178. In Some problems for biological fishery survey and techniques for their solution. A symposium of the Inter. Comm. for the Northwest Atlantic Fisheries. France 1956. Parsons, J. W. 1958. Fishery management problems and possibili- ties on large southeastern reservoirs. Trans. Am. Fish. Soc. 87(1957): 333-355. Pashkov, G. D., V. M. Kruglova, and L. M. Malovitskaya. 1957. Features of the formation of aquatic vegetation in the Veselyi Reservoir. Pp. 448-455. In Trans. Sixth Conf. on the Biol. of Inland Water. M. Raveh (trans. from Russian). The National Science Foundation, Washington, D.C. 284. 285. 286. 287. 288. 289. 290. 291. 292. 293. 294. 295. 296. 248 Paterson, C. G., and C. H. Fernando. 1970. Benthic fauna colonization of a new reservoir with particular reference to the Chironomidae. Jour. Fish. Res. Bd. Canada 27(2): 213-232. Patriarche, M. H., and R. S. Campbell. 1958. The development of the fish population in a new flood-control reservoir in Missouri, 1948 to 1954. Trans. Am. Fish. Soc. 87(1957): 240-258. Paulet, M., H. Kohnke, and L. J. Lund. 1972. An interpretation of reservoir sedimentation: I. Effect of watershed characteristics. Jour. of Environ. Qual. 1(2): 146-150. Peltier, W. H., and E. B. Welch. 1970. Factors affecting growth of rooted aquatic plants in a reservoir. Weed Sci. 18: 7-9. Penfound, W. T. 1956. Primary production of vascular aquatic plants. Limnol. & Oceanogr. 1: 92-101. Petr, T. 1968a. Development of bottom fauna in the man-made Volta Lake in Ghana. Verh. Int. Verein. theor. angew. Limnol. 17(1): 273-282. . 1968b. Population changes in aquatic invertebrates living on two water plants in a tropical man-made lake. Hydrobiologia (The Netherlands) 32(3-4): 449-484. 1970. Macro-invertebrates of flooded trees in the man-made Volta Lake (Ghana) with special reference to the burrowing mayfly, PoviZZa adhsta Navis. Hydrobiologia (The Netherlands) 36(3-4): 373-398. Pholprasith, S., and N. Waiwutto. 1971. Fish transplantation in Ubolratana Reservoir. Annual report of the Ubolratana Reservoir Fishery Developmental Unit, pp. 128—130. (In Thai). Pierce, P. C., and H. M. Yawn. 1965. Six field tests using two species of Tilapia for controlling aquatic vegetation. Proc. Southern Weed Conf. 18: 582-3. Pirozhnikov, P. L. 1968. Increasing the fish production of large reservoirs. Jour. of Ichthyology 8(1): 40-48. . 1972. The biOproductional effect of the impoundment of large rivers and its importance for fishery economy. Verh. Int. Verein. theor. angew. Limnol., Stuttgart 18: 822-832. , A. F. Karpevich, et a1. 1969. Biological principles for improving fisheries in inland waters. Jour. of Ichthyol. 9(5): 744-751. 297. 298. 299. 300. 301. 302. 303. 304. 305. 306. 307. 308. 309. 249 Poddubuyi, A. G. 1963. On the significance of submerged forests for the fish population of the Rybinsk Reservoir. (Trans- lated from Russian). Biological Abstracts 46(8): #32643, 1965. 1968a. Duration of the formation of fish schools in the Volga Reservoir. Pp. 62-68. In Biological aspects of water reservoirs. Translated from Russian. The National Science Foundation, Washington, D.C. 1968b. The importance of flooded forests for the fish population of a reservoir. Pp. 69-79. In Biological aspects of water reservoirs. Translated from Russian. The National Science Foundation, Washington, D.C. Poon, C. P. C., and F. J. DeLuise. 1967. Manganese cycle in impoundment water. Wat. Resource Bull. 3(4): 26-35. Porcella, D. B., J. S. Kumagai, and E. J. Middlebrooks. 1970. Biological effects on sediment-water nutrient interchange. Jour. Sanit. Engr. Div., ASCE. 96(SA 4): 911-926. Posey, F. H., Jr., and J. N. DeWitt. 1970. Effects of reservoir impoundment on water quality. Jour. Power Div. ASCE. 96 (PO 1): 173-185. Prah, S. K. 1969. Observations on parasitic infection in freshwater fishes of Ghana. Pp. 261-268. In Man-Made Lakes. L. E. Obeng (ed.), The Accra Symposium. Ghana Universities Press, Accra. Prescott, G. W. 1962. Relationships of phytoplankton to lake productivity, pp. 34-49. In Algae of the Western Great Lakes area with an illustrated key to the Genera of Desmids and freshwater Diatoms. Wm. C. Brown Company Publisher, Dubuque, Iowa. 977 p. Prevost, G. 1957. Use of artificial and natural spawning beds by lake trout. Trans. Am. Fish. Soc. 86(1956): 258—260. Prirozhnikov, P. L. 1961. The zooplankton of reservoirs and its significance for the nutrition of fish. Translated from Russian. Biological Abstracts 45(7): #27256, 1964. Prochazkova, L. 1966. Seasonal changes of nitrogen compounds in two reservoirs. Verh. Int. Verein. theor. angew. Limnol. 16(2): 693-700. Prowse, G. A. 1953. The role of phytoplankton in studies on productivity. Verh. Int. Verein. theor. angew. Limnol. 12(1): 159-163. . 1969. The role of cultured pond fish in the control of eutrophication. Verh. Int. Verein. theor. angew. Limnol. u, 310. 311. 312. 313. 314. 315. 316. 317. 318. 319. 320. 321. 250 Pyrina, I. L. 1966. Primary production of the phytoplankton in the Ivankovo, Rybinsk, and Kuibyshev reservoirs and its dependence on certain factors. Pp. 263-287. In Production and circulation of organic matter in inland waters. M. Yariv (trans. from Russian). The National Science Founda- tion, Washington, D.C. Quennerstedt, N. 1958. Effect of water level fluctuation on lake vegetation. Verh. Int. Verein. theor. angew. Limnol. 13: 901-906. Rawson, D. S. 1953. Morphometry as a dominant factor in the productivity of large lakes. Verh. Int. Verein. theor. angew. Limnol. 12(1): 164-175. Rawstron, R. R., and K. A. Hashagen, Jr. 1972. Mortality and survival rates of tagged largemouth bass (Microptems salmoides) at Merle Collins Reservoir. Calif. Fish and Game 58(3): 221-230. Reeves, T. G. 1972, Nitrogen removal: A literature review. Jour. Wat. Poll. Contr. Fed. 44(10): 1895-1908. Reid, G. K. 1961. Ecology of inland waters and estuaries. Reinhold Publishing Corporation, New York. 375 p. Ricker, W. E. 1958. Handbook of computations for biological statistics of fish populations. Fish. Res. Bd. Canada Bull. No. 119, 300 p. Ridley, J. E. 1970. The biology and management of eutrophic reservoirs. Jour. Wat. Treatment and Examination 19 (part 4): 374-393. , and J. M. Symons. 1972. New approaches to water quality control in impoundments. Pp. 389-412. In Water pollution microbiology. R. Mitchell (ed.). John Wiley & Sons, Inc., New York. Robson, D. S., and H. A. Regier. 1968. Estimation of population number and mortality rates. Pp. 124-158. In Methods for assessment of fish production in fresh waters. W. E. Ricker (ed.), IBP Handbook No. 3. Blackwell Scientific Publication, Oxford and Edinburgh. Roeder, M., and R. H. Roeder. 1966. Effect of iron on the growth rate of fishes. Jour. Nutrition 90(1): 86-90. Roll, Y. V., Y. Y. Tseeb, et a1. 1957. The Kakhovka Reservoir in the first year of its existence. Pp. 415-427. In Trans. Sixth Conf. on the Biol. of Inland Waters. M. Raveh (Trans. from Russian). The National Science Founda- tion, Washington, D. C. 322. 323. 324. 325. 326. 327. 328. 329. 330. 331. 332. 333. 334. 251 Rounsefell, G. A., and W. H. Everhart. 1953. Fishery science, its methods and applications. John Wiley & Sons, Inc., New York. 444 p. Royal, L. A., and A. C. Cooper. 1960. Dams as barriers or deterrents to the migration of fish. Pp. 93-100. In the Seventh Tech. Meet..of IUCN, Theme 1, Vol. IV. Athens, Greece. Runnstrom, S. 1953. Changes in fish production in impounded lakes. Verh. Int. Verein. theor. angew. Limnol. 12(1): 176-182. 1960. Hydro-electric power stations and fishing. Pp. 61-68. In the Seventh Tech. Meet. of IUCN, Theme 1, Vol. IV. Athens, Greece. Russell-Hunter, W. D. 1970. Aquatic productivity: An introduc- tion to some basic aspects of biological oceanography and limnology. The Macmillan Company, New York. 306 p. Rutkovskii, V. I., and A. S. Kireeva. 1957. Main features of the oxygen regime of the Rybinsk Reservoir. Pp. 315-325. In Trans. Sixth Conf. on the Biol. of Inland Waters. M. Raveh (trans. from Russian). The National Science Founda- tion, Washington, D.C. Ryder, R. A. 1965. A method for estimating the potential fish production of north-temperate lakes. Trans. Am. Fish. Soc. 94(3): 214-218. 1970. Major advances in fisheries management in North American glacial lakes. Pp. 115-127. .In A century of fisheries in North America. N. G. Benson (ed.), Am. Fish. Soc., Spec. Publ. No. 7. Rzoska, J. 1966. The biology of reservoirs in the U.S.S.R. Pp. 149-153. In Man-Made Lakes. R. H. Lowe-McConnell (ed.), Academic Press, London. Sadek, S. E. 1970. An electrochemical method for removal of phosphates from waste water. Fed. Wat. Qual. Adm't., Dept. of the Interior. 47 p. Sailer, R. I. 1972. Biological control of aquatic weeds - recent progress. Proc. Northeastern Weed Sci. Soc. 26: 180-182. Sakamoto, M. 1966. Primary production by phytOplankton community in some Japanese lakes and its dependence on lake depth. Arch. Hydrobiol. 62: 1-28. Sande, T. V. 1966. Fishways. Pp. 153-156. In Inland fisheries management. A. Calhoun (ed.), Calif. Dept. of Fish and Game. E.‘IIT. _.‘:I’Jl ‘- V 335. 336. 337. 338. 339. 340. 341. 342. 343. 344. 345. 346. 347. 348. 252 Sawyer, C. N., and P. L. McCarty. 1967. Chemistry for sanitary engineering. McGraw-Hill Book Company, New York. 518 p. Schaefer, M. B. 1951. Estimation of size of animal population by marking experiments. Fish and Wildl. Service, Fish. Bull. 52: 191-203. Schindler, D. W. 1971. Carbon, nitrogen, and phosphorus and the eutrOphication of freshwater lakes. Jour. Phycology 7: 321-329. , and J. E. Nighswander. 1970. Nutrient supply and pri- mary production in Clear Lake, eastern Ontario. Jour. Fish. Res. Bd. Canada 27: 2009-2036. , and G. W. Comita. 1972. The dependence of primary production upon physical and chemical factors in a small, senescing lake, including the effects of complete winter oxygen depeletion. Arch. Hydrobiol. 69(4): 413-451. Schmulbach, J. C., and H. A- Sandholm. 1962. Littoral bottom fauna of Lewis and Clark Reservoir. Proc. South Dakota Acad. Sci. 41: 101-112. Schnabel, 2. E. 1938. The estimation of the total fish popula- tion of a lake. Ann. Math. Monthly 45(6): 348-352. Schumacher, F. X., and R. W. Eschmeyer. 1943. The estimate of fish populations in lakes or ponds. Jour. Tenn. Acad. Sci. 18(3): 228-249. Seaman, D. E., and W. A. Porterfield. 1964. Control of aquatic weeds by the snail, Marisa cornuarietis. Weeds 12(1): 87-92. Seeley, C. M., and G. W. McCommon. 1966. Kokanee. Pp. 274- 294. In Inland fisheries management. A. Calhoun (ed.), Calif. Dept. of Fish and Game. Sewell, W. D. 1970. Diquat residues in two New York lakes. Proc. Northeastern Weed Contr. Conf. 24: 281-2. Sguros, P. L., T. Monkus, and C. Phillips. 1965. Observations and techniques in the study of the Florida manatee - reticent but superb weed control agent. Proc. Southern Weed Conf. 18: 588. Sharonov, I. V. 1966. Formation of reservoir fish fauna. Transl. from Russian. Biological Abstracts 48(9): #94414, 1967. Shields, J. T. 1958a. Environmental control of carp reproduc- tion through water drawdowns in Fort Randall Reservoir, South Dakota. Trans. Am. Fish. Soc. 87(1957): 23—33. 349. 350. 351. 352. 353. 354. 355. 356. 357. 358. 359. 360. 253 1958b. Fish management problems of large impoundments on the Missouri River. Trans. Am. Fish. Soc. 87(1957): Shiraishi, Y., and S. Kimura. 1971. Distribution of fishes and environmental condition in artificial lakes of Thailand. Bull. of Freshwat. Fish. Res. Lab., Tokyo 21(1): 47-58. (In Japanese, English summary). Sidthimunka, A., M. Potaros, et a1. 1968. Observation on the hydrology and fisheries of Ubolratana Reservoir (1965- 1966). Indo-Pacific Fisheries Council, FAO Regional Office for Asia and the Far East, Bangkok, Thailand. Occasional Paper 69/3: 18 p. Silvo, O. 1967. Studies on the use of paraquat as a means of controlling canadian pondweed (Elodea canadensis) in Finland. Pp. 102-108. In,A symposium of European weed Research Council. Sisler, F. D. 1960. Bacteriology and biochemistry of the sedi- ments. Pp. 187-193. In Comprehensive survey of sedimenta- tion in Lake Mead, 1948-49. USGS Prof. Paper 295. Smirnov, N. N. 1963. On the seasonal distribution of inshore Cladocera of the Volga water reservoirs. Hydrobiologia 22: 202-207. Smith, S. H. 1954. Method of producing plastic impressions of fish scales without using heat. Prog. Fish-Cult. 16(2): 75-78. Smith, S. F. 1972. Effects of a thermal effluent on.aquatic life in an East Texas Reservoir. Proc. 25th Ann. Conf. SE. Ass. Game and Fish Comm., pp. 374-384. Smith, G. E., and T. F. Hall. 1967. Eurasian watermilfoil in the Tennessee Valley. P. 160. In A symposium of European Weed Research Council. August 1967. Smith, L. L., and D. M. Oseid. 1972. Effects of hydrogen sulfide on fish eggs and fry. WAter Research 6(6): 711-720. Smith, J. R., J. R. Pugh, and G. E. Monan. 1968. Horizontal and vertical distribution of juvenile salmonids in Upper Mayfield Reservoir, Washington. U. S. Fish and Wildl. Service. Spec. Sci. Rept. - Fisheries No. 566, 11 p. Sokolova, N. Y. 1957. The chironomid (Tendipedid) fauna of the Ucha Reservoir and its seasonal dynamics. Pp. 300-304. In Trans. Sixth Conf. on the Biol. of Inland Waters. M.Raveh (translated from Russian). The National Science Foundation, Washington, D.C. 361. 362. 363. 364. 365. 366. 367. 368. 369. 370. 371. 254 Somme, S. 1960. The effects of impoundment on salmon and sea trout rivers. Pp. 77-80. In the Seventh Tech. Meet. of IUCN, Theme 1, Vol. IV. Athens, Greece. Spall, R. D., and R. C. Summerfelt. 1969. Host-parasite rela- tions of certain endoparasitic helminths of the channel catfish and white crappie in an Oklahoma Reservoir. Bull. Wildl. Disease Ass. 5: 48-67. Sparrow, R. A. H., P. A. Larkin, and R. A. Rutherglen. 1964. Successful introduction of Mysis relicta Loven into Kootenay Lake, British Columbia. Jour. Fish. Res. Bd. Canada 21(5): 1325-1327. Speece, R. E. 1970. Aeration of oxygen-deficient impoundment releases. Advances in Water Pollution Research. Volume 2. S. H. Jenkins (ed.). Paper III-29: 1-11. Sreenivasan, A. 1967. Primary production and fish yield in a tropical impoundment, Stanley Reservoir, Mettur Dam, Madras State, South India. Proc. National Inst. of Sci. of India, New Delhi 35(2: Part B): 125-130. 1970. Limnology of trOpical impoundments: A compara- tive study of the major reservoirs in Madras State (India). Hydrobiologia 36(3—4): 443-469. , R. S. Raj, and K. F. Antony. 1964. Limnological studies of tropical impoundments. II. Hydrobiological features and plankton of Bhavanisagar Reservoir (Madras State) for 1961-62. Proc. Indian Acad. Sci. 59(part B): 53-71. Stepanek, M. 1960. Limnological study of the Reservoir Sedlice near Zeliv. X. Hydrobioklimatological Part: The rela- tion of the sun radiation to the primary production of nannoplankton. Sci. Pap. Inst. Chem. Tech. Prague, Czechoslovakia, Fac. Technol. Fuel Wat. Vol. 4, Pt. 1, pp. 21—142. 1965. Numerical aspects of nannoplankton production in reservoirs. Pp. 291-308. In Primary productivity in aquatic environments. C. R. Goldman (ed.), Univ. of Calif., Berkeley and Los Angeles. Straskraba, M. 1965. Contribution to the productivity of the littoral region of pools and ponds. I. Quantitative study of the littoral zOOplankton of the rich vegetation of the backwater Labicko. Hydrobiologia 26: 421-443. Stroud, R. H. 1955. Harvests and management of warmwater fish populations in.Massachusetts' lakes, ponds and reservoirs. Prog. Fish-Cult. 17(2): 51-62. __ .4_.— ____— _— _ __ _ _ _ flu - ‘(l 1m... E. -4 372. 373. 374. 375. 376. 377. 378. 379. 380. 381. 382. 383. Stumm, Sukhoi, Summerfelt, R. c. 1971. Factors influencing the horizontal ' __1 Surber, Swan, A. A. B. 1967. Toxicological problems in the control of F1 Swingle, H. S. 1947. Experiments on pond fertilization. Ala. 255 1966. American experience in recreational use of artificial waters. Pp. 189-199. In Man-Made Lakes. R. H. Lowe-McConnell (ed.), Academic Press, London. W., and J. J. Morgan. 1970. Aquatic chemistry; an intro- duction emphasizing chemical equilibria in natural waters. Wiley—Interscience, New York. 583 p. , and E. Stumm-Zollinger. 1972. The role of phosphorus in eutrophication. Pp. 11-42. In Water pollution micro- biology. R. Mitchell (ed.), Wiley-Interscience, New York. 416 p. spawning grounds downstream from the Kakhovka Hydro- electric station. Translated from Russian. Biological Abstracts 48(3): #11229, 1967. Van, P. G. 1959. Experiment in the use of artificial E3 ‘i a -1 distribution of several fishes in an Oklahoma reservoir. Pp. 425-439. In Reservoir Fisheries and Limnology. G. E. Hall (ed.), Am. Fish. Soc., Spec. Publ. No. 8. , and M. C. Warner. 1970. Incidence and intensity of infection of Plistophora avarice, a.microsporidian para- site of the golden shiner, Notemigonus crysoleuoas. Pp. 142-160. In A symposium on diseases of fishes and shell- fishes. S. F. Snieszko (ed.), Am. Fish. Soc., Spec. Publ. No. 5. E. W. 1961. Improving sport fishing by control of aquatic weed. Fish and Wildl. Service, Bur. of Sport Fish. & Wildl., Circular 128, 37 p. water weeds. Pp. 161-167. In A symposium of the European “a. Weed Research Council, August 1967. Exper. Sta. Bull. 264, 34 p. ; z 1957. Control of pond weeds by use of herbivorous Ed fishes. Proc. Southern Weed Conf. 10: 11-17. _ 1970. Production of the threadfin shad, Dorosoma petenense (Gunther). Proc. 23rd Ann. Conf. SE. Ass. Game and Fish Comm. (1969): 407-421. Sylvester, R. O. 1960. Some influences of multi-purpose water usage on water quality. Pp. 215-235. In the Seventh Tech. Meet. of IUCN, Theme 1, Vol. IV. Athens, Greece. 256 384. . 1963. Effects of water uses and impoundments on water temperature. Pp. 6-28. In Water temperature influences, effects, and control. Proc. of the Twelfth Pacific Northwest Symposium on Water Pollution Research. Fed. Wat. Poll. Contr. Adm't., Northwest Region, Corvallis, Oregon. November 1963. 384. , and R. W. Seabloom. 1965. Influence of site character- istics on quality of impounded water. JAWWA 57(12): 1528-1546. 385. Symons, J. M. 1969. Discussion of effect on benthic algae on stream dissolved oxygen. Pp. 147-154. In Water quality behavior in reservoirs. J. M. Symons (compiled). U. S. Dept. of Health, Education and Welfare. PBS - Pub. No. 1930. 386. , and G. G. Robeck. 1969. Calculation technique for destratification efficiency. Pp. 355-362. In Water quality behavior in reservoirs. J. M. Symons (compiled). ' ' U. S. Dept. of Health, Education and Welfare. PBS-Publ. “J No. 1930. 387. , W. H. Irwin, and G. G. Robeck. 1969. Control of reservoir water quality by engineering methods. Pp. 449- 484. In Water quality behavior in reservoirs. J. M. Symons (compl.). U. 8. Dept. of Health, Education and Welfare. PHS-Publ. No. 1930. 388. , R. M. Clark, et a1. 1969. Management and measurement of D0 in impoundments. Pp. 155-168. In Water quality behavior in reservoirs. J. M. Symons (compiled). U. 8. Dept. of Health, Education and Welfare. PBS-Publ. No. 19 30. F] 389. , J. K. Carswell, and G. G. Robeck. 1970. Mixing of 22,_ water-supply reservoirs for quality control. JAWWA 62(5): 322-334. 390. , W. F. Echelberger, et a1. 1971. .Artificial destrati- fication in reservoirs. JAWWA 63(9): 597-604. .3 I”, 391. Task Group for Evaporation Control Report. 1963. Survey of methods for evaporation control. JAWWA 55: 157-168. 392. Task Committee Assigned to Inventory Sedimentation Research Needs to Water Quality of Hydraulics Division. 1971. Influences of sedimentation on water quality: An inventory of research needs. ASCE Jour. Hydraulic Div. 97(HY 8): 1203-1212. 393. Taylor, M. P. 1971. PhytOplankton productivity response to nutrients correlated with certain environmental factors in six TVA reservoirs. Pp. 209-217. In Reservoir Fisher- ies and Limnology. G. E. Hall (ed.), Am. Fish. Soc., Spec. Publ. No. 8. 394. 395. 396. 397. 398. 399. 400. 401. 402. 403. 404. 405. 406. 257 Tesch, F. W. 1968. Age.and growth. Pp. 93-123. In.Methods for assessment of fish production in fresh waters. W. E. Ricker (ed.), IBP Handbook No. 3, Blackwell Scientific Publications, Oxford and Edinburgh. The U. 8. President's Science Advisory Committee. 1967. The world food problem. Vol. II. The White House. 772 p. Thompson, W. H. 1955. Problems of reservoir management. Trans. Am. Fish. Soc. 84(1954): 39-46. Tomnatik, E. N. 1957. The formation of the ichthyofauna of the Dubossary Reservoir. Pp. 400-405. In Trans. Sixth Conf. on the Biol. of Inland Water. M. Raveh (trans. from Russian). The National Science Foundation, Washington, D.C. Trefethen, P. S. 1968. Fish-passage research, review of progress, 1961-66. Bur. of Comm. Fish., Circular 254, 24 p. Turner, W. R. 1971. Sport fish harvest from Rough River, Kentucky, before and after impoundment. Pp. 321-330. In Reservoir Fisheries and Limnology. G. E. Hall (ed.), Am. Fish. Soc., Spec. Publ. No. 8. Tyurin, P. V. 1968. Underlying biological.principles of the control of fishing in inland waters. Jour. of Ichthyology 8(3): 377-390. Umnov, A. A. 1971. Application of the mathematical stimulation method to the study of the role of photosynthesic aeration of lakes. The Soviet Jour. of Ecology 2(6): 489-494. van Busschbach, E. J., and H. Elings. 1967. The use of dichlobenil against aquatic weeds in ditches and ponds. Pp. 130-137. In A symposium of the European Weed Research Council, August 1967. Van Oosten, J. 1929. Life history of the lake herring (Leucichthys artedi Le Sueur) of Lake Huron as revealed by its scales, with a critique of the scale method. Bull. U. S. Bur. Fish., 44: 265-428. Vincent, R. 1971. River electrofishing and fish population estimates. Prog. Fish-Cult. 33(3): 163-169. Vukovic, T. 1970. Annulus formation on the scales of the Uchinsk Reservoir roach. Jour. of Ichthyology 10(4): 515-518. Wadjowicz, Z. 1964. The development of ichthyofauna in dam reservoirs with small variations in water level. ACTA Hydrobiol. 6(1): 61-79. 407. 408. 409. 410. 411. 412. 413. 414. 415. 416. 417. 418. 419. 258 Ware, F. J. 1966. The use of cOpper sulfate as a method of partial control of elodea (Elodia dbnaa) in Lake Thonosassa, Florida. Hyacinth Control Jour. 5: 17-18. Warren, G. E. 1971. Biology and water pollution control. W. B. Saunders Company, Philadelphia. 434 p. Waters, T. F., and R. C. Ball. 1957. .Lime application to soft- water, unproductive lake in northern Michigan. Jour. Wildl. Management 21(4): 385-391. Weatherley, A. H. 1972. Growth and ecology of fish populations. Academic Press, New York. 293 p. WEbSter. D. A. 1962. Artificial spawning facilities for brook F3 trout, Salvelinus fontinalis. Trans. Am. Fish. Soc. “ 91(1961). Welch, P. S. 1948. Limnological methods. McGraw-Hill Book _ Company, Inc., New York. 381 p. E}. Weldon, L. W., and W. C. Durden. 1970. Integrated biological and chemical control of aquatic weed. Proc. 23rd Ann. Meet. Southern Weed Sci. Soc., p. 282 (abstract). Westlake, D. F. 1965. Some basic data for investigations of the productivity of aquatic macrOphytes. Pp. 229-248. In Primary productivity in aquatic environments. C. R. Goldman (ed.), Univ. of California Press, Berkeley and Los Angeles. Wiebe, A. H. 1931. Notes on the exposure of several species of pond fishes to sudden changes in pH. Trans. Am. Micro. Soc. 50: 380—383. *1 1960. The effects of impoundments upon the biota of p the Tennessee River system. Pp. 101-117. In the Seventh I Tech. Meet. of IUCN, Theme 1, Vol. IV. Athens, Greece. Winberg, G. G., and O. N. Bauer. 1971. Productivity and principles of the management of inland waters in the H USSR. Freshwater Biology 1(2): 159-169. Wisniewski, T. F. 1965. Improvement of the quality of reservoir discharges through turbine or tailrace aeration. Pp. 299-308. In Symposium on streamflow regulation for quality control. Robert A. Taft Sanit. Engr. Center, Cincinnati. PHS Publ. No. 999-WP-30. Wohlschlag, D. E. 1952. Estimation of fish populations in a fluctuating reservoir. Calif. Fish and Game 38(1): 63-72. 420. 421. 422. 423. 424. 425. 426. 427. 428. 429. 430. 431. 432. 259 Wood, R. 1951. The significance of managed water levels in developing the fisheries of large impoundments. Jour. Tenn. Acad. Sci. 26(3): 214-235. , and D. W. Pfitzer. 1960. Some effects of water level fluctuations on the fisheries-of large impoundments. Pp. 118-138. In the Seventh Tech. Meet. of IUCN, Theme 1, Vol. IV. Athens, Greece. , and T. L. Sheddan. 1971. Norris Reservoir fertilizer study. I. Effects of fertilizer on food chain organisms and fish production. Jour. Tenn. Acad. Sci. 46(3): 81-89. Worthington, E. B. 1966. Introductory survey. Pp. 3-6. In 5.? Man-Made Lakes. R. H. LowerMcConnell (ed.), Academic " 4 Press, London. 218 p. p 1 Wright, J. C. 1967. Effect of impoundments on productivity, 5 water chemistry, and heat budgets of rivers. Pp. 188— ‘ . i 199. In Reservoir Fishery Resources Symposium. Univ. 1) of Georgia, Athens. * Wunderlich, W. 0., and R. A. Elder. 1967. The influence of reservoir hydrodynamics on water quality. Pp. 78-94. In Proc. 6th Ann. Sanit. Wat. Res. Engr. Conf., Nashville, Tennessee. June 1967. Wyatt, H. N., and H. D. Zeller. 1962. Fish population dynamics following a selective shad kill. Proc. 16th Ann. Conf. SE. Ass. Game and Fish Comm. (1962): 411-417. Yakovino, J. T. 1970. Distribution and abundance of the zoo- plankton of Canton Reservoir, Oklahoma. Proc. Okla. Acad. Sci. 50: 87-90. Yakovleva, A. N. 1966. The state of natural reproduction and of the fish stocks in the Volgograd Reservoir. Translated from Russian. Biological Abstracts 49: #54895. 1969. Determining factors of fish productivity in the Volgograd Reservoir. Jour. of Ichthyology 9(3): 446-449. Yeo, R. R. 1967. Silver dollar fish for biological control of submerged aquatic weeds. Weeds 15: 27-31. Younger, R. R. 1958. Preliminary studies using Kuron as an aquatic herbicide. Proc. 12th Ann. Meet. Northeastern Weed Contr. Conf., PP. 332-337. Zajic, J. E. 1971. Water pollution disposal and reuse. Volume 1. Marcel Dekker, Inc., New York. 389 p. 260 433. Zeller, H. D., and H. N. Wyatt. 1967. Selective shad removal in southern reservoirs. Pp. 405-414. In Reservoir Fishery Resources Symposium. Univ. of Georgia, Athens. 434. Zhadin, V. 1., and S. V. Gerd. 1961. Fauna and flora of the rivers, lakes, and reservoirs of the U.S.S.R. Translated from Russian by A. Mercado, 1963. The National Science Foundation, Washington, D.C.