j???” xv |° ~ mowcmu (31:31:55 Amleiumzus m MICHIQAN mm 3 31193111 far thy Degree of M. S. MICHIGAN STATE, COLLEGE H (award ' D avid Tail“ 1.951 THE-SIS lag-Mi g _'.' ' ' \ 1 V ‘ ‘ ' '. , I . \ » .' " "|llil-l—ll-llii .._ J _‘.-.__ a}; . , 1 _ ‘ .51 ":1?! 3 1293 10149 1399!!l . A - ' ‘ 1 \' . - L13 1 4 ‘ “ LEE-gm " ’ ‘ ‘h I up! ’ L ' , _. 1... - ._________ 1 . . . This is to certify that the p } . thesis entitled 5' . " ' fProduction of Bass and Bluegill: 1n ': Michigan Ponds". ' a 1’. presented by ‘ . Howard D. Tait ‘ z? 1" lf'v . a '1 , has been accepted towards fulfillment '. , of the requirements for ' } ‘ ‘1 no 8. degtee in ZOOIOa " ‘ 1f. 1 ' \ a . J l. Major professor L 7' 3.1 ' ' Date “a: lb, 1951. - ., {1 0-169 PRODUCTION OF BASS AND BLUEGILLS IN MICHIGAN PONDS By Howard David gait. A THESIS Submitted to the School of Graduate Studies of Michigan State College of Agriculture and Applied Science in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE Department of Zoology 1951 Section I II III IV VI WI VIII TABLE OF CONTENTS INTRODUCTION ................................ ACKNOWLEDGMENTS ............................. DESCRIPTION OF EXPERIMENTAL PONDS ........... METHODS AND EQUIPMENT ....................... StOCking Rates 0.0.00...0.000000000000000 Fertilization ........................... Chemical Methods ........................ Draining Operations ..................... Procedure for Measuring Fish ............ THE INTERRELATIONSHIPS OF LARGEMOUTH BLACK BASS AND BLUEGILLS IN POIqDS 00.0.000000000000 EXPERIMENTAL STOCKING OF ADULT BLUEGILLS AND FINGERLING BLUEGILLS IN COMBINATION WITH LARGEMOUTH BLACK BASS 00.00000000000000000... Ponds Stocked with Fingerling Bluegills and Fingerling Largemouth Bass .......... Ponds Stocked with Adult Bluegills and Fingerling LargemOUth 8355 00000000000... FISH POPULATION BALANCE IN EXPERIMENTAL PONDS 0.000.000.0000000000.000000000000000... F/C Ratio 000.0.00.00.0000000000000000000 Y/C Ratio 0.0.0.0.0.00.00.00.000000000000 value 00.000.00.000.0.000000000000000. Evalue 0.000.000.000.0000000.00.00.00... A, I, andsvalues 0000.00.00.00000000000 THE EFFECTS OF VEGETATION ON THE SURVIVAL OF YOUNG-OF-THE-YEAR BLUEGILLS 0.000000000000000 CROPPING OF FISH IN EXPERIMENTAL PONDS 000000 255880 Page 1 A 5 11 ll 12 13 18 19 20 22 25 30 39 #0 A6 A7 A9 52 55 \.1 \I II. \I . . J I ‘ ll - ) s r n f a O m w o . I I 1 . w a . . u I u I I u 0 7 n s n P . v v I a o 1 I D v 7 1 f Q n . n . 5 . I o . . ~ 0 \ o .. 1 1 1 t I a I . $ . I n D C o 0 . . d o l . A . Q n a a 1 s ) e s i n 0 v a a. Q a I L . I a 4 t n . . I n . I 5 I. a a ... a . u I A x a u a s 2 A I n a 1 s e 1 0 n a o . A I 1 - V r a o A w . J a v 0 l 3 I a O Q l I u v A . o x a 1 . 1 s 1 a . o s o I I n s a a I 1 n I O I V I s p D O [It'll I a 9 a I J I 5 O a O R I 9 l I J a U n. ’ 9 w. ) n n. n I 1 0 O I n A ) n. u 1 o i I a A v 9 O I 4 I 1 t n p n 1 t. r r I t. B n A \ O a .I n s I v 4 s 4 V \ 7 A Q l I n Q 1 I I n 3 I (III [I all! [I III- III. 4!! III . I t a c O. O a . I 1 n 0 \ C ) . ‘ t 1 h .J ... I e . . t 7 u I J a ‘ Q a a . s l v a Q r. a 2 . o a . ‘ C o p ) no a J a O I q n C .. ., 1 a 4 C > V o TABLE OF CONTENTS Section Page X INCREASING POND PRODUCTIVITY BY THE USE OF FERTILIZER .00...OOOOOOOOOOOOOOOOOOOOOO... 57 Comparison of the Yield of Fish from Fertilized and Unfertilized Ponds ....... 57 Cost of Fertilizer in Relation to Increased Yield of Edible-Size Fish ..... 61 The Effects of Fertilizer on Higher Aquatic Vegetation OOOOOOOOOOOOOOOOOOOOOO 61" XI DISCUSSION 0 O O O O O O O O O O O O O O O O O O O 0 O O O O O O O O O O O O O 76 XII S UTVHVIARY O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O 81 XIII LITERATURE CITED 0 O O O 0 O O O O O O O O O O O O O O O O O O O O O O O 85 INTRODUCTION The practice of raising fish in ponds to provide food for man is very old, beginning in China centuries ago. It spread throughout the world and in many countries of Europe and Asia fish are now cultivated intensively in ponds and provide an important part of the food economy of those countries. The beginning of the practice of cultivating fish in ponds in America is obscure, however it has been important since fish hatcheries began supplying fish for planting programs. Active interest in the develop- ment of farm ponds to augment natural fishing waters, and research on pond management have been of fairly recent origin, beginning about 1930 with investigations concerning the problems of producing black bass in hatcheries (Davis and Wiebe, 1930; Hogan, 1933; and Meehean, 1933). Following these pioneering studies investigators have concentrated on several different approaches to the problems of pond management. Some investigators have been concerned with increasing the yield from ponds by artificial fertilization (Surber, 1943; 2 Bennett, 19h6; Swingle and Smith, 1939). Others have analyzed the total production of ponds and the yield of fish to fishermen and applied the results of their efforts to the management of natural waters (Ricker, 19h6; Moyle, l9h9; Swingle, 1950). The relationships of predator and prey species have also received attention (Bennett, 19A8; Swingle l950)and the most recent investigations have been directed toward determining species combinations and ratios that will produce fish crops useful to man when stocked in newly developed ponds. Establishing stocking recommendations for Michigan ponds is one of the objectives of this present report. Michigan has many lakes, and probably has little need for farm ponds to provide fishing, however, ponds have multiple uses such as stock watering, boating, swimming, and conserving ground water supplies in addition to recreational fishing. Ponds are also becoming important in Michigan for raising bait minnows for sale to fishermen. Although much research has been done in other states concerning the production of fish in farm ponds, the differences in length of growing season, ‘1~A'||>l\'l|ll|\.[[’l'li y.||\('ll. {lll‘ll‘ {.[llllbl‘l‘il‘ .[\ l[r [lllll II III 5" and soil and water fertility in Michigan, make it necessary to establish stocking and management policies applicable to Michigan ponds. The experiments described in this report were designed to evaluate fish stocking combinations, and the role of fertilizer in the management of Michigan ponds. ACKNOWLEDGMENTS This work was made possible by a cooperative program between Michigan State College and the Institute for Fisheries Research of the Michigan Department of Conservation. Materials, equipment, and supervision were provided by the College and the Institute gave financial assistance and provided for the use of the hatchery facilities where these experiments were conducted. The author wishes especially to thank Dr. Robert C. Ball for his guidance and assistance in conducting this investigation, and the Institute for Fisheries Research for making this work possible. The author would also like to express his appreciation to the men of the Wolf Lake State Fish Hatchery for their assistance and cooperation in the management and draining of the experimental ponds. DESCRIPTION OF EXPERIMENTAL PONDS The experiment described in this report was conducted at Wolf Lake State Fish Hatchery located ten miles west of Kalamazoo, Michigan. Detailed descrip- tions of the ponds have been given in an earlier pub- lication, Patriarche and Ball (1949) and are only briefly reviewed here. Three pairs of ponds were selected for this experiment on the basis of similarity of size, basin shape, and bottom type. One of each pair of ponds was fertilized with inorganic fertilizer, and the other served as a control, so that each experimental combination of bass and bluegills could be tested in a fertilized pond and in an unfertilized pond. Figure 1 shows the relative positions, and source water of the ponds at Wolf Lake Hatchery, with fertilized and unfertilized ponds designated. The water supplying these hatchery ponds comes from three springs and is high in carbonate hardness. Methyl orange alkalinity tests of the Springs showed 160 parts per million. Water levels were maintained in the ponds and no water was allowed to overflow Figure 1. Diagram of Ponds at Wolf Lake State Fish Hatchery PUMP" LINE ATCHERY NO. l 917 PARK POND \ V I, , ’1 /, // .¢.~:::;§:::-::::\<“.;;was:,. ,.:SEEfE§{»SS$‘§ES§%§E§§£1i(11‘.fiat:' _s1§§§§§§§§§§§>1$.S}‘.»\‘E§§‘.-S§‘.~9‘ ;Sffifssiifffififififfifis9“‘ '( ( «« (m ‘ . “A ~‘<<»~.,):::w 1.‘;§§${§§§§:‘$§§1,‘§=.. c ‘ ,,\1»\:§S'ZSES)X\‘§“Z»-$§iz ~:a:a:a~=:;§s;x>$§;;§mw "*’\%s\\\&§;;§§::;a:;::§az - ~_.. “'I‘tfu‘ww ,mnlfi‘fli‘13) «(M (PH i)\"i‘>‘):\)fi§)§)fi(§>) £1828 mum <( (( ms n»)?! fifipimil , «A < Ir Q's-nus, ‘ , ) n . “u"k’ ‘(1 «mm 1212::.féséxx‘ixfikmm A(\u.t,«((x(((((((( ((\ «(NW M‘nnnhm) h mm "As(.pp((‘((‘_(((.(f_(ll(' WOLF LAKE HATCHERY - FERTILIZED - UNFERTIUZED ‘ :qmufr ummlmamb ‘ ”“U H . ‘ ~mmfi‘h“Mm - , I ;. "I““WH _‘ .‘ J"H'ASwiffx‘y.‘is‘:“f“‘-f"i'wi )1 ) H‘ ‘ (“((Uummm "Hump/K, "'Iflllwu. :1 :muumm H mm ""“m: h at the outlet. However, in all ponds there was some seepage through the bottom, and loss by evaporation. The surface area of these ponds ranged from 1.3 acres to 2.3 acres, and the basin of the ponds sloped gradually to a maximum depth of 6 feet at the drainage outlet. The bottom was a mixture of sand and marl with muck in the deepest parts of the ponds. A filamentous algae mat began to develop on the surface of the fertilized ponds during the first summer of the experiment and on some ponds became more ex- tensive each successive summer. Submerged higher aquatic vegetation was very abundant in both fertilized and unfertilized ponds at the beginning of the experiment in 19h7. Anacharis, ghggg, Ngigg and two species of potamogeton were off major importance in all ponds at first, but as the experiment progressed Anacharis became dominant in the unfertilized ponds. Figure 2 illustrates the very abundant growth of this plant in the unfertilized ponds during late summer. The dominance of vegetation changed in fertilized ponds also, however these changes were associated with fertilization and are described in detail in another section of this report. Figure 2. Dense Growth of Higher Aquatic Vegetation in Unfertilized Pond 'r h.""? ~ ‘ukn ’3’, I". )0, ' ‘91‘,' METHODS AND EQUIPMENT Stocking Rates The ponds were stocked with either adult or finger-- ling bluegills (Lepomis macrochirus) and yearling large- mouth black bass Micropterus salmoides). The bass were stocked on April 15, and the bluegills on May 20, 1947. Table 1 shows the numbers, stocking rates, and the average total length of each species when stocked. TABLE I Stocking Data Pond Species Total Approx. Average Total ‘ Number Number Length in (Acres) Per Acre Inches 20 Bass 345 150 4.1 (1.8) Bluegill 41 18 6.5 21 Bass 330 150 4.0 (2.3) Bluegill 39 18 6.5 12 Bass 240 150 4.0 (1.8) Bluegill 86 50 6.5 7 Bass 225 150 4.0 (1.5) Bluegill 76 50 6.5 17 Bass '500 -390 4.4 (1.3) Bluegill 3,300 2.540 2.7 9 Bass '850 '500 4.4 (1.7) Bluegill 5,100 3,000 2.7 12 Fertilization Commercial inorganic fertilizer was applied at the rate of 100 pounds per acre every three weeks from the middle of May until August 7th, which was approximately three weeks before the ponds were drained. Several methods of applying fertilizer have been tried for ponds of this type including distribution from a boat, mechanical pumping, and broadcasting by hand (Figure 3). Broadcasting from shore or from a boat rowed around the pond seemed to be efficient methods for these small ponds, however better distribution of fertilizer was possible when the operator waded about the pond with a pail or tub of fertilizer than when the fertilizer was simply thrown from shore. Attempts to obtain a more even coverage by spraying a mixture of fertilizer and water over the pond with a centrifical pump were abandoned when it was found that the sand filler in the fertilizer clogged the pump mechanism. The commercial fertilizer used in this experiment was of 6-10-4 and 10-6-4 (N—P205-K20) grade. The first figure of this analysis gives the percentage of total nitrogen; the second figure represents the percentage of available phosphoric acid (P205), and the last figure 13 represents the percentage of water-soluble potash.(K20). 10-6-4 fertilizer was applied during the summers of 1947 and 1948, but became unavailable in 1949. 6-10-4 was used in 1949 instead. Chemical Methods The temperature of the water at several stations in each pond was taken at regular intervals with two thermom- eters; a Taylor Maximum-Minimum, and a pocket thermometer. Figure 4 is a graph of the temperatures recorded during the summer of 1949 in pond 12. The water temperatures of the otherexperimental ponds did not vary significantly from pond 12. The dissolved oxygen content, carbon dioxide, methyl orange alkalinity, and pH were also measured at frequent intervals in all ponds in an effort to detect differences among the ponds that could be attributed to fertilization. The amounts of free carbon dioxide in the waters of ponds 7, 9, 20, and 21 were high during the month of July, ranging from thirteen to thirty-eight parts per million. A series of measurements of dissolved oxygen content made at various depths showed that during periods of high carbon dioxide oxygen levels at three feet became very Figure 3 Broadcasting Fertilizer by Hand ”HM“ n " '33., "‘ 4 N" ,4 7"", v '3“. L 5;: Q {1.“g.'.'r 510 r' ,: l" \q' Figure 4 Water Temperatures of Pond 12 during the Summer of 1949 ON q EmDUD< 0H 1 MA:% ON OH mash ON OH l.om 1 am 1 mm 1 mm [am 1 mm ION \an 1 mm mm Om Hm mm 1mm I LLL mc This is presumed to be a result of bass predation on young bluegills as there was very little vegetation present in this pond. This combination of fingerling bass and adult blue- gills stocked at the rate of 150 bass and 50 bluegills per acre is apparently more satisfactory than stocking fingerlings of both species if large bass are desired, but not if edible-size bluegills are wanted the first year. The significant difference in the size of bass from these ponds in 1948, is illustrated by Figure 5 which shows individual fish representing the average from pond l7 and the average from Pond 12. Figure 5 Samples from Pond 17 (left) and Pond 12 (right)i Representing the Average Size of Largemouth Bas at Draining, 1949 35 Ponds 20 and 21 Ponds 20 and 21 were stocked originally with approx- imately 150 largemouth bass and 18 adult bluegills per acre, but during the summer of 1947 a few of each species escaped from pond 20 into pond 21 through a defective screen. Pond 21 was not fertilized except that some water from pond 20, which was fertilized, was released into pond 21 to maintain the water level. Pond 21 had a very dense growth of aquatic plants, chiefly figfigg and thgg, during the experiment. Pond 20 also had an abundant growth of higher aquatic plants, and in addition a thick filamentous algae mat covered progressively more of the pond each summer of the experiment. Pond 20 produced the greatest poundage of fish of this experiment, yielding approximately 720 pounds per acre when the pond was drained in 1948. Bass had made good growth in this pond and produced young in 1948. The bulk of the population consisted of small bluegills rang- ing in size from 1.5 to 4.1 inches. The population in pond 21 was similar to that in pond 20 in that both species had reproduced and the per- centage by weight composition was about the same (Figure 6). Figure 6 Composition of Fish Populations in Successive Years in Fertilized and Unfertilized Ponds Stocked with Fingerling Largemouth Bass and Adult Bluegills. PON D 2 O FERTIUZED SMALL BIiEGlllS SMALL BLUEGILLS I948 I949 PERCENT BY WEIGHT POND 2| UNFERTIUZED LARGE sass BASS LG.BG SMALL BLUEG ILLS BLUEGILLS I948 ' I949 38 However, the bass in pond 21 had not grown as rapidly, and the total weight of fish was considerably less than in pond 20. Again in 1949, Pond 20 (fertilized) produced the greatest weight in pounds per acre of all ponds studied, and comparitively the production in Pond 21 (unfertilized) was poor. The composition of the populations in pond 20 and pond 21 were similar with respect to percentage by weight, but the bass in pond 21 were in very poor condition, having lost weight during the period between pond drainings. The combination of 150 fingerling largemouth bass and 18 adult bluegills tested in two ponds produced a satisfactory population composition and maximum yield in the fertilized pond, and a population of emaciated fish in the unfertilized pond. This combination then, was not satisfactory in an unfertilized pond that was filled with higher aquatic plants. Eighteen adult bluegills per acre were sufficient to establish a bluegill population in these ponds. FISH POPULATION BALANCE IN EXPERIMENTAL PONDS Several criteria have been developed by H. S. Swingle (1950) for judging fish population balance. These criteria were developed after examining the results of many experi- ments with pond fishes and therefore were considered as a means of evaluating the populations of the experimental ponds with which this present report is concerned. Swingle described a balanced fish population as one that yields, year after year, crops of harvestable fish that are satisfactory in amount when the basic fertilities of the bodies of water containing these populations are considered. Ability of the species within the population to reproduce, and control of the numbers of fish by carnive-l rous species are also necessary in a balanced population. The interrelationships between the various groups of fish in a balanced population are discussed at some length in Swingle's excellent paper. In the following section the relationships or criteria of pond balance proposed by Swingle are reviewed and applied to the data concerning the populations of fish in these experimental ponds in Michigan to further evaluate the various combinations of bass and bluegills tested. 40 The F/C Ratio This is the ratio of the total weight of all forage fishes to the total weight of all carnivorous fishes in a population. Bass are the carnivorous component and bluegills the forage component in a bass-bluegill combination such as was stocked in these Michigan ponds. Swingle found the desirable range for F/C values to be between 3.0 and 6.0 with values below 2.0 indicating overcrowding of bass and values above 10.0 indicating a large p0pulation of medium and small bluegills. The F/C values and other relationships for the popu- lations from Wolf Lake ponds are summerized in Table 3. Judged by F/C ratios alone most of the ponds were crowded with bass, with the exception of ponds 9 and 20. Figures 6, 7 and 8 also show the composition of the pOpulations from these ponds by percentage of total weight. F/C ratios are well worth considering, for when carnivorous species are overcrowded predation on forage species is excessive and not enough small forage fish escape to replace adults as they are removed. The low F/C ratio of pond 12 during 1948 and 1949 indicates that this pond was overcrowded with bass. No small bluegills were among TABLE III Relationships Between Species and Between Groups in Fish Populations in Experimental Ponds in Michigan Pond Year F/C Y/C At E Values A I S Ratio Ratio Value Bass Bluegill Bluegill Values 20 1948 4.0 4.0 20.3 19.8 80.2 1.6 .... 98.4 1949 3.5 2.2 46.2 22.6 77.4 34.5 65.5 .... 21 1948 5.0 1.7 36.6 34.8 65.1 5.3 .... 94.7 1949 2.0 .3 62.5 32.0 67.9 54.3 31.7 14.0 12 1948 105 103 [+3.0 [+300 5703 05 0000 9905 1949 1.5 ... 96.2 44.7 55.3 100.0 .... .... 7 1948 3.0 2.8 28.7 25.6 74.4 4.2 .... 95.8 1949 1.3 .1 77.1 45.7 54.3 80.1 13.5 6.4 17 1948 3.0 1.3 68.3 22.6 77.4 59.5 .... 40.5 1949 2.0 1.0 66.8 32.2 67.8 25.5 26.9 47.6 9 1948 9.0 2.4 67.2 9.6 90.3 74.4 .... 25.6 1949 4.0 .5 85.6 20.4 79.6 80.0 8.3 11.7 Figure 7 Composition of Fish Populations in Successive Years in Fertilized and Unfertilized Ponds Stockai With Fingerling Largemouth Bass and Adult Bluegills ' ____ _——_— — _- POND I 2 FERTI UZED BLUEGILLS l948 1949 PERCENT BY WEIGHT POND 7 UNFERTIUZED BLUEGILLS BLUEGILLS l948 I949 44 Figure 8 Composition of Fish Populations in Successive Years in Fertilized and Unfertilized Ponds Stocked with Fingerling Largemouth Bass and Fingerling Bluegills POND l7 'FERTILIZED BLUEGILLS I948 l949 PERCENT BY WEIGHT PON D 9 UNFERTIUZED BLUEGILLS I948 46 the fish present at draining in 1949 and it is assumed that this was due to the overcrowding of bass. The Y/C Ratio The Y/C ratio as defined by Swingle equals the Y value, or the total weight in ponds of all those indi- viduals in the "F" group that are small enough to be eaten by the average-sized adult in the "C" species in a population. In this present experiment bluegills that were two to three inChes long and numbered one hundred or more per pound were considered to be small enough to be eaten by the bass. This is quite arbitrary, because the maximum size bluegill that could be swallowed by the largest bass in these ponds was not determined. Swingle found that Y/C ratios in balanced ponds ranged from 0.02 to 4.8 and that between 0.02 to 0.5 all populations were so severely overcrowded with "C" species that they probably should be considered "temporarily balanced" because the bass were unable to gain weight and in fact lost weight, while insufficient numbers of bluegills were surviving to utilize available food. This situation existed in pond 21 of this experiment which had a Y/C ratio of .3 at draining in 1949 and in which the bass lost weight. However, each year there were many 47 small bluegills present when this pond was drained indicating that some other factor was operating to prevent good growth of the bass. In this pond heavy growths of aquatic vegetation were probably a contribut- ing factor to the poor condition of the bass. The condition of the population of Pond 20 as in- dicated by Y/C ratios of 4.0 in 1948 and 2.2 at drain- ing 1949 should be considered to be balanced. The Y/C ratios of other pond populations fell below the desirable range of 1.0-3.0 recommended by Swingle. By his standards these ponds would be considered to be overcrowded with bass. In all ponds studied the Y/C ratios were consider- ably less at draining in 1949 than at draining the previ- ous year. The At Value The At value (total availability value) is defined as the percentage of the total weight of a fish population, composed of harvestable size fish. In this experiment 8.3 inches for bass and 5.0 inches for bluegills were considered to be minimal sizes in con- sidering harvestable fish. The At values for these ponds therefore, are not strictly comparable with the At values 48 given by Swingle who used minimum sizes of .4 pounds for bass and .1 pounds for bluegills. This change of standards for minimum harvestable size for Michigan experimental ponds was made so as to include some fish that did not quite reach the minimum of .l or .4 pound and yet seemed worth cleaning for table use. All ponds originally stocked with adult bluegills had At values in the inefficient or unbalanced range when the populations were examined in 1948. As would be expected since no cropping of large fish was done, the At values increased in 1949. A In ponds 9 and 17, originally stocked with fingerling bluegills, high At values in 1948 reflect the large crop of harvestable bluegills that were present. The At value 96.2 of pond 12 in 1949 is an indication of the overcrowding of this pond with bass. The E Values The E value of a species or group is the percentage of weight of the entire population composed of that species or group. Swingle found that the average E values in twenty- six balanced populations containing only bluegills and 49 largemouth bass were 22.8 for bass and 77.2 for bluegills. E values for these experimental ponds in Michigan are also listed in Table III. Pond 20, E values were very close to the optimum listed above, while E values for bass from Ponds 7, 12, and 21 were higher than the pro- posed desirable range for balanced populations. E values seemed to be fairly stable from year to year for these ponds. A, I, and S Values In his study of the relationships between various groups within a species Swingle defined A, I, and S values as the percentage of the total weight of a species con- sisting of large, intermediate, and small fish respectively. Large fish are those of harvestable or edible-size, and intermediate are those which escape predation by bass and are available to replace large fish as they are removed. Small fish are those fish small enough to be eaten by the large bass and are usually young-of-the-year. The most desirable part of the range of A values for bluegills in balanced populations as recommended by Swingle was from 60 to 80, and the minimum value was 35.5. It can be seen from Table III that A values for bluegills in these Michigan ponds ranged from .5 to 100 per cent. 50 A values for these ponds changed considerably from 1948 to 1949. Ponds 21, 7, and 9, all unfertilized, were the only ponds which had A values within the desired part of the range from 60 to 80. In both balanced and unbalanced ponds Swingle found that the intermediate group of bluegills normally made up less than 7 per cent of the total weight. No inter- mediate size bluegills were present in any of the Michigan ponds at draining in 1948. In the ponds originally stocked with adult bluegills the spawn of 1947 and 1948 were not yet large enough to be considered as intermediate. In the ponds originally stocked with fingerling bluegills, fingerlings had grown beyond the intermediate stage and were all considered as large. I values were high for most ponds at draining in 1949 indicating that too many blue- gills were surviving bass predation. S values for bluegills were given by Swingle as being most desirable between 15 and 40 with values in excess of 60 unsatisfactory and values less than 10. indicating that the ponds were overcrowded with bass. The Michigan ponds originally stocked with adult bluegills had excessively high S values for bluegills when the ponds were drained in 1948 and very low values when the ponds were drained in 1949. In the ponds stocked 51 with fingerling bluegills the S values for bluegills did not change much from 1948 to 1949 and were approx- imately within the desired range of 15 to 40 each year. THE EFFECTS OF VEGETATION ON THE SURVIVAL OF YOUNG-OF-THE-YEAR BLUEGILLS Fertilization affects the dynamics of a bass-bluegill population by increasing the fish-food organisms, and by altering the habitat of the fish. Patriarche and Ball (1949) and others, have shown that the application of fer- tilizer in proper amounts will increase the standing crop of fish food organisms. Swingle (1949) found in experi- ments in southern ponds that fertilization alters the habitat of pond fishes by killing higher aquatic vegetation, and that this reduces the cover for young bluegills. As a result, the largemouth bass are able to reduce the popu- lation of young fish to the extent that most of the weight of bluegills is in the form of large fish. The populations of fish from the experimental ponds at Wolf Lake Hatchery were examined to compare the abundance of young-of-the-year bluegills in ponds having several different densities of vegetation. Under the conditions of this experiment no particular survival trends were noted. The data from these ponds are somewhat contradictory and are presented (Table IV) to show the survival of young bluegills under variable conditions of vegetative cover. 53 TABLE IV Number of Young-of-the-Year Bluegills per Acre at Draining in Successive Years 1948 1949 Pond Density of Number of' Density of Number of" Vegetation Bluegills Vegetation Bluegills 20 Ioderate 91,591 Ioderate 0 21 Heavy 29,408 Heavy 2,826 7 Heavy 28,788 Heavy 1,584 12 Moderate 5,609 Scarce O 9 Very Heavy 12,410 Heavy 7,470 17 Heavy 333380 Heavy 2.335 In pond 12, which had a considerable reduction of aquatic plants following fertilization, there was an excellent survival of young bluegills one year and none the next year. Pond 20, with a partial plant density reduction after fertilization produced large numbers of small bluegills in 1948 but not in 1949. Similarly, in pond 21, which remained almost filled with aquatic vegetation during the same period, a large percentage of the total weight of fish was in small bluegills only one 54 year. It can be seen from the above table that ponds with similar densities of vegetation showed considerable variation in the number of young bluegills present at draining. In all ponds, both fertilized and unfertilized, there was a much smaller proportion of young-of-the-year bluegills present at draining in 1949 than in 1948. The near absence of young bluegills in some ponds may have been due to poor spawning conditions during 1949. Occasionally in Michigan bluegills fail to spawn in lakes and ponds, possibly due to low water temperatures. During 1950, for example, cool temperatures prevailed throughout most of the summer, and production of young bluegills was reported to be poor in many sections of the state. Tadpoles and crayfish were very abundant in these ponds during the summer of 1948, but not in 1949. These organisms are bass food and undoubtedly served as a buffer to effective control of small bluegills by bass. CROPPING OF FISH IN EXPERINENTAL PONDS There was no cropping of fish from these ponds during the experiment except for the loss of small bluegills which occurred each year when the ponds were drained. Table V shows the weight of fish at draining in 1948, the fish lost in handling, and the weight of fish at drain- ing in the fall of 1949. TABLE V Weight of Fish at Draining in Successive Years Pond Total Weight Weight of Weight of Total Weight of Fish at Fish Lost Fish Restocked of Fish at Drainin 1948 At Draining in Pond Drainin l949 (Pounds? (Pounds) (Pounds) (Pounds? ‘ 20 1298 520 778 1209 21 611.5 179.5 , 432 546.5 12 385.5 88.7 296.8 366.8 7 . 382.5 58.6 323.9 315 By draining time 1949 the total weight of fish in each pond was nearly equal to the weight present before the mortality occurred in 1948. Therefore, the weight present in each pond in 1948 can be presumed to be the carrying capacity of that pond. Krumholz (1948) has 56 suggested that the term carrying capacity should signify the upper limit of the weight of a species or combination of species that can be supported by a body of water over an extended period of time. INCREASING POND PRODUCTIVITY BY HE USE OF FERTILIZER It has been shown repeatedly that the application of fertilizers will increase the numbers and weight of fish that a pond will produce. The extensive research of Swingle (1947) in Alabama, Surber (1943) in Virginia, and many others has shown that an increased production of fish resulted when nutrients were added to ponds. The method of fertilizing and the results obtained vary with the locality under observation. Similarly, the mechanism by which added nutrients increase productivity has been inter- preted differently by each of several authors. Not all localities are infertile to the extent that fertilization is needed. Bennett (1943) found that many small artificial lakes in Illinois were naturally fertile, and concluded that increasing production in those lakes by fertilization was not justified. This variability in results of fertilization in various localities prompted the testing of fertilization as a means of increasing production in Michigan Ponds. Comparison of The Yield of Fish From Fertilized and Unfertilized Ponds Ball (1949) compared fertilized and unfertilized ponds in Michigan and reported significant differences 58 in the abundance of fish-food organisms, and some evidence of greater production of fish, attributable to the addition of fertilizer. In this present experiment the evaluation of the addition of fertilizer in producing more fish in Michigan ponds is continued. Each combination of bass and bluegills previously described was tested in a pond fertilized with commercial inorganic fertilizer and also in a pond that received no fertilizer. A summary of the total weight in pounds per acre of each species and the weight of edible-size fish for each pond is given in Figure 9. The total weight in pounds per acre for all fish in the ponds each year at draining were as follows: 20 21 12 7 l7 9 Year (Fert.) (Fert) (Fert.) 1948 721 ' 266 214 256 193 379 1949 669 237 203 209 194 196 The total yield for fertilized ponds ranged from 193 to 721 pounds per acre and for unfertilized ponds from 196 to 379 pounds per acre. When each pair of ponds is con— sidered separately there appears to be no significant Figure 9 Standing Crop of Bass and Bluegills in Experimental Ponds at Draining in Successive Years owNDmeu CNN-dhmmuza owNijmn— owNJmeuza CNN-1:...mw... omN_._.._.mw..—ZD on 020“. a ozod N. ozoa ”020.. t ozoa m ozoa mcm. QVQ m3. m¢m_ 9V2 mcm. mtm. 3m. mg. m¢m. m¢2 3m. . . mam. . . . \ I 0 mm mm mm 1 2 mm mm mm mm 7 mm mm Mm 1 8. mm mm I e. .......... III. CON 000000 Ill 8N ...... l on» 93.833 3.9398 g I ooe @36me ....< a ll 00¢ mmqm 1502853 3.9593 I . mm