' W‘—"v'~—‘— I AGE, GROWTH AND FOOD HABITS OF THE ROUND wnnmsa, mosomum CYLINDRACEUM (PALMS), m CENTRAL LAKE MICHIGAN Thesis for the Degree of M. S; MiCHIGAN STATE UNIVERSITY mm W. ARMSTRONG 1973 IIIIIIIIIIIIIIIIIIIIIIIIIIIIIII 3 1293 10699 6790 " LIBRAR Y 5""? '. ‘1'. : fl bunngan ante pin-Um varsity W; OCT 2 0 2005 f k! e; 0 55 u ABSTRACT AGE, GROWTH AND FOOD HABITS OF THE ROUND WHITEFISH, PROSOPIUM CYLINDRACEUM (PALLAS), IN CENTRAL LAKE MICHIGAN BY John W. Armstrong This study was undertaken to update age and growth information for the round Whitefish, Prosopium cylindraceum (Pallas), in Lake Michigan and to investigate seasonal variations in the food of the round Whitefish. Scale samples, stomach samples and certain morpho- metric data on the round Whitefish were collected several times each month from April through November of 1972. Growth in length was determined by scale analysis. A body-scale relationship was derived and back-calculated lengths were tabulated. A reversal of "Lee‘s phenomenon" was noted, with older fish showing progressively greater growth at a given age. Several possible reasons for this phenomenon are discussed. Length-weight relationships and condition factors were calculated and compared on a seasonal basis. John W. Armstrong No statistical differences were found between males and females with respect to length or weight at a given age. However, females of a given age tended to be slightly longer and heavier than their male counterparts. The round whitefish of central Lake Michigan were found to be the fastest growing of any population of round whitefish yet studied. The fish in this study had the greatest average total length for every year of life and the greatest weight for most lengths. Fish from more northern localities grew slower, matured later and lived longer. The major food items of round whitefish in central Lake Michigan are aquatic insects, with Chironomidae being by far the most important. Hirudinea, Mollusca, Decapoda and fish eggs are also very important food items. Details are given on the seasonal fluctuation of these items in the round whitefish diet. AGE, GROWTH AND FOOD HABITS OF THE ROUND WHITEFISH, PROSOPIUM CNIJNDRACEUM (PALLAS), IN CENTRAL LAKE MICHIGAN BY John WJ Armstrong A THESIS Submitted to Michigan State University in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE Department of Fisheries and Wildlife 1973 ACKNOWLEDGMENTS I would like to acknowledge Michigan State University, Department of Fisheries and Wildlife, for pro- viding me with a research assistantship and for the use of their facilities. I wish to express my appreciation to Consumers Power Company of Michigan for funding this study and for supplying all of the equipment necessary for conducting this research. I wish to thank Dr. P. I. Tack, Dr. E. W. Roelofs, and Dr. T. W. Porter for their helpful suggestions and cheerful outlooks on life. Special thanks are in order for Dr. C. R. Liston, the Ludington Research Project Field Director in residence, who added several dimensions to the experiences gained from this study. I also wish to thank my fellow graduate students Dan Brazo, Tom Chiotti, Greg Olson and Larry Green for helping me collect these data and for their comaraderie. Thanks also to my friend Deetsy Merickel for things too numerous to mention. ii TABLE OF CONTENTS Page ACKNOWLEDGMENTS . . . . . . . . . . . . ii LIST OF TABLES . . . . . . . . . . . . V LIST OF FIGURES . . . . . . . . . . . . Vi INTRODUCTION . . . . . . . . . . . . . 1 DESCRIPTION OF AREA SAI'IPLED o o o o o o o o 4 MATERIALS AND METHODS . . . . . . . . . . 8 Sampling Methods . . . . . . . . . 8 Scale Preparation and Reading . . . . . . 9 LIFE HISTORY OF THE ROUND WHITEFISH . . . . . 12 AGE AND GROWTH . . . . . . . . . . . . 17 Total Length-Standard Length Relationship . . 17 Age Composition and Length-Frequency Distribution . . . . . . . . . . 18 Body- Scale Relationship . . . . . . . 22 Calculated Length at Each Annulus . . . . . 25 LENGTH-WEIGHT RELATIONSHIP AND CONDITION . . . . 33 Length-Weight Relationship . . . . . . . 33 Condition . . . . . . . . . . . . . 40 SEX RATIO AND MATURITY . . . . . . . . 43 Sex Ratio . . . . . . . . . . . . . 43 Maturity . . . . . . . . , . . . . 44 FOOD HABITS . . . . . . . . . . . . . 46 Methods of Food Analysis . . . . . . . . 47 Analysis of Food Habits . . . . . . . . 58 iii Page S UlvllV/lARY 0 O O O O C O O O O O O D O O 6 2 LITERATURE CITED . . . 66 APPENDIX . . . . . . . . . . . . . . 70 iv Table LIST OF TABLES Page Length frequency distribution at capture of round whitefish of different age groups collected between September 8, 1972 and November 15, 1972 in central Lake Michigan . 19 A comparison of the lengths of round white- fish caught by various mesh sizes of gill nets in central Lake Michigan between April 26, 1972 and November 15, 1972 . . . 2O Calculated total length at the end of each year of life of round whitefish from central Lake Michigan . . . . . . . . . . . 27 Average calculated total lengths at each annulus formation of round whitefish from North American lakes . . . . . . . . . 31 Average calculated and empirical weights for each age-group of round whitefish caught from September 1, 1972 through November 15, 1972 in central Lake Michigan . . . . . . 35 Average calculated weights at each annulus formation of round whitefish from North American lakes . . . . . . . . . . . 39 Average condition of the round whitefish of central Lake Michigan for each age and season of the year . . . . . . . . . 41 Food items eaten by round whitefish in central Lake Michigan between April 1, 1972 and November 15, 1972 . . . . . . . . . . 48 Seasonal percent frequency of occurrence of food items present in round whitefish stomachs of central Lake Michigan . . . . . . . . 57 LIST OF FIGURES Figure Page 1. Map of the Ludington pumped storage project showing the locations of the permanent fish sampling stations in Lake Michigan . . . . 5 2. Average number of fish caught per gill-net lift each month during 1972 . . . . . . . . 14 3. Average absolute and incremental growth in length for 233 round whitefish from central Lake Michigan . . . . . . . . . . . 29 4. The average length—weight relationship for 233 round whitefish from central Lake MiChigan O O I O O O O O O O 0 O . 36 5. Spring food habits of the round whitefish in central Lake Michigan . . . . . . . . 51 6. Summer food habits of the round whitefish in central Lake Michigan . . . . . . . . 53 7. Fall food habits of the round whitefish in central Lake Michigan . . . . . . . . 55 vi INTRODUCTION The round whitefish, Prosopium cylindraceum (Pallas), is a fish of northern waters. In North America the species is found in all of the Great Lakes except Lake Erie and ranges north to the Arctic Ocean. It is present in the streams and lakes of Canada and occurs in the drainage systems of the St. Lawrence River and Hudson Bay (Slastenenko, 1958). In this century, the annual commercial catch of round whitefish in Lake Michigan reached its peak in 1929 with a catch of 359,000 pounds (Baldwin and Saalfeld, 1962). After 1929 the commercial catch steadily declined to a low of 10,000 pounds or less from 1956 to 1960. From 1961 to the present the round whitefish catch has steadily increased to 144,000 pounds in 1969 (Lyles, 1969). It appears from these commercial catch records that an upward trend is occurring in round whitefish production in Lake Michigan. Only two previous age and growth studies have been conducted on round whitefish of the Great Lakes. Bailey (1963) used data collected during 1958-1960 from western Lake Superior and Mraz (1964) used data collected during 1951 from northern Lake Michigan. The present study was conducted to update age and growth data for the round whitefish in Lake Michigan and to investigate seasonal variations in the food of the round whitefish. The fish sample used in this study was collected in conjunction with environmental studies of Lake Michigan carried out in 1972 by Michigan State University, Department of Fisheries and Wildlife. Consumers Power Company of Michigan contracted Michigan State University in 1971 to conduct a six—year study of possible effects which their Ludington, Michigan Pumped Storage Hydro- electric Plant might have on the aquatic ecosystem in the adjacent areas of Lake Michigan. The Ludington pumped storage plant is located on the eastern shore of Lake Michigan, approximately four miles south of Ludington, Michigan. A reservoir with a volume of 27 billion gallons has been built over 350 feet above the Lake Michigan water level. During weekday evenings and on weekends when electrical demand is low, electrical power supplied by other power plants in Michigan will be used to pump water from Lake Michigan into the reservoir. During weekdays when electrical demand rises, the stored water will be transferred back to Lake Michigan and will generate electricity by turning six 312 megawatt turbines as it falls. It has been estimated that when all six turbines are operable, a maximum of 17 billion gallons of water may be transferred at a maximum water flow of 75,960 cfs during generation and 66,600 cfs during pumping. This will simulate a large river flowing alternately into and out of Lake Michigan. The pumped storage plant is scheduled to begin operation in 1973. During 1972 various environmental studies were conducted in the areas adjacent to the plant. These studies included surveys of periphyton, phytoplankton, zooplankton, benthic organisms and fish populations. The round whitefish were collected in conjunction with these fish population surveys. If future studies in the area adjacent to the pumped storage project in the coming years should show major changes in the rate of growth, abundance or food of the round whitefish, some change in the aquatic ecosystem in this area may be indicated. DESCRIPTION OF AREA SAMPLED The Ludington Pumped Storage Hydroelectric Power Plant is located four miles south of Ludington, Michigan on the eastern shore of Lake Michigan. Six fish-collection stations were chosen in the immediate area of the plant (Figure 1). Station one (43°51'00" N Lat, 86°27'20" W Long) was established three miles south of the plant breakwater at.a depth of twelve meters and serves as the control station for environmental impact comparisons. Station two (43°52'45" N Lat, 86°26'50" W Long) is one mile SSE of the southernmost jetty and is eight meters deep. Station three (43°53'5" N Lat, 86°27'20" W Long) is one- half mile south of the breakwater and is fourteen meters deep. Station four (43°53'30" N Lat, 86°29'00" W Long) is one and one-half miles WSW of the breakwater and is twenty-four meters deep. Station five (43°54'20" N Lat, 86°27'35" W Long) is one-half mile NNW of the breakwater and is twelve meters deep. Station six (43°54'50" N Lat, 86°27'10" W Long) is one mile north of the northern jetty of the plant and is six meters deep. The bottom material at these stations is composed of mixtures of fine sand, gravel, boulders and clay outcrops. Figure 1.--Map of the Ludington pumped storage project showing the locations of the permanent fish sampling stations in Lake Michigan. 6 l/I/I/I/I/I/ / LUDINGTON ’//// PERE MARQUETTE O LAKE LAKE MICHIGAN BASS LAKE LUDINGTON PUMPED STORAGE PROJflECT SAMPLING STATIONS 1 SCALE OF MILES A.” The dissolved oxygen in the sampling area during the sampling period ranged from 9 to 15 parts per million and the pH ranged from 7.7 to 8.5. Water temperatures at the bottom of each station ranged from a low of 2°C on April 10, 1972 to a high of 20°C on August 28, 1972 and the final low temperature in the fall was 7°C on November 15, 1972. The major fish species in the area, by order of number caught, were yellow perch (Perca flavescens), alewife (Alosa pseudoharengus), longnose sucker (Catostomus catostomus), white sucker (Catostomus commersoni), lake trout (Salvelinus namaycush) and round whitefish (Prosopium cylindraceum). MATERIALS AND METHODS Sampling Methods Round whitefish were collected from April 10 through November 15, 1972 by gill nets. At each of the six previously mentioned sampling stations a BOO-foot gang of nylon gill nets was set for a 24-hour period four or five times each month, weather permitting. Each gang of nets was composed of six fifty-foot panels, one each of 2, 2%, 3, 4, 42 and 7-inch stretched mesh. An additional fifty-foot, 1—inch stretched mesh panel was added to each gang of nets on July 27, 1972. A11 gill net panels were six feet deep. An otter trawl was used for several short trawling runs in April but clay outcrops on the lake bottom pre- vented this trawl from catching any fish. A rectangular, iron framed Helgoland trawl and a meter net on an aluminum sled navigated the bottom more successfully. However, after approximately six hours of trawling in May, June, July and August no round whitefish and very few other fish were caught. Trawling runs were made in the immediate vicinity of the six sampling stations and between 8 A.M. and 5 P.M. A total of 370 round whitefish were caught in the gill nets during this study. They were removed from the nets, placed in plastic bags, put on ice and processed immediately upon reaching shore. Total lengths, from the tip of the snout to the tip of the caudal fin with the lobes compressed, were measured to the nearest millimeter. Standard lengths, also to the nearest millimeter, were measured from the tip of the snout to the hidden bases of the caudal fin rays, where a groove forms naturally when the tail is bent from side to side. Weights were measured on a spring balance and read to the nearest gram. Sex, date of capture, and specimen number, were also recorded for all fish taken. The stomachs from all fish were dissected out, labeled by specimen number, placed in individual cheesecloth bags and preserved in ten percent formalin. Scale Preparation and Reading The method of age determination was that of scale interpretation. This method has been shown to be valid for various coregonids by Van Oosten (1923), Hile (1936), McHugh (1941) and Van Oosten and Hile (1949). Because of this evidence for other coregonines, it has been assumed that this method is also valid for the round whitefish. Scales were removed from the left side of the fish midway between the lateral line and the anterior insertion 10 of the dorsal fin. No attempt was made to take key scales (scales taken from the same scale row and at the same point on each fish) for this study. From five to ten scales from each fish were placed between pieces of cellulose acetate and impressions were then made of these scales as described by Smith (1954). These impressions were then examined at a magnification of 22 diameters on a Bausch and Lomb micrOprojector. All scales were read twice without reference to the length of the fish. No fish were discarded as having totally unreadable scales. Aging many of the round whitefish scales proved to be difficult because of accessory marks or checks which resembled true annuli. These accessory marks generally form in the fall of the year and may be related to the development of the gonads and the high protein demand which this development may create. When proteinaceous growth of the fish resumes, a new ridge begins to form at the anterior edge of the scale, proceeds around the lateral edges and eventually encircles the scale. This new ridge "cuts across" other incomplete circuli to complete an accessory mark or false annulus in the early fall (Keeton, 1965). True annuli may normally be differentiated from false annuli by having many more closely spaced circuli (representing a period of slow growth) before the annulus 11 and more widely spaced circuli (representing periods of greater growth) immediately after the annulus. From magnified impressions of the scales, positions of the annuli in relation to the focus were measured along the scale radius on scale cards graduated in millimeters. The radius was measured as the greatest distance from the focus to the anterior scale margin of an average size scale for each fish. A nomoqraph was used in determining back calculated lengths of each fish at the time of each annulus formation. Age-groups, representing age in years, are desig- nated by Roman numerals corresponding to the number of annuli present. On January 1 of each year it is assumed that a fish becomes one year older, even though the annulus for this year may not form until spring or summer (Hile, 1936). LIFE HISTORY OF THE ROUND WHITEFISH The round whitefish is one of the least studied of the coregonids, or whitefishes, with only three detailed studies having been completed by Bailey (op. cit.) and Mraz (Op. cit.) and Normandeau (1969). One of the main goals of the age and growth studies by Bailey and Mraz was to establish a practical commercial size limit for the round whitefish. Normandeau investigated Spawning habits and fecundity. The round whitefish is also known by common names such as menominee, pilot and shadwwiter. This species is slender and cigar shaped, little compressed, except at the head and tail, and uniformly tapered. It is much more cylindrical in cross section than the more laterally com- pressed lake whitefish, Coregonus clupeaformis. However, round whitefish and lake whitefish are often sold together commercially as "whitefish." Young round whitefish (under 180 millimeters in total length) usually have 7 to 13 dark, oval parr marks on each of their sides (McPhail and Lindsey, 1970). However, in the present study three round whitefish between 138 and 154 mm had no visible parr marks. 12 13 Age and size at maturity, as well as the exact spawning time, vary from lake to lake. Spawning generally occurs in late fall, either over shallow reefs or in mouths of streams and rivers. The fish normally spawn over honeycomb rock or gravel in 4 to 12 meters of water (Koelz, 1929). In the present study, the number of fish caught per gill-net lift at each sampling station varied inversely with water temperature as shown in the tables of the Appendix. However, the average number of fish caught per gill-net lift at each sampling station varied much more by month (or season) of the year than by water temperature. These monthly differences (Figure 2) are due mainly to the fish coming in to shallower waters in the fall to spawn. Slastenenko (op. cit.) states that pearl organs often form on the sides of the bodies of both males and females during.the spawning season. Normandeau (op. cit.) found that pearl organs were much more prominent on the males than on the females just prior to spawning. No pearl organs were observed in this study as late as November 15, 1972. Normandeau (op. cit.) found the number of eggs per female ranged from 2,200 to 9,445 in Newfound Lake, New Hampshire, and Bailey (op. cit.) found the range to be from 1,076 to 11,888 eggs per female in western Lake Superior. 14 Figure 2.--Average number of fish caught per gill-net lift each month during 1972. Average Number of Fish Caught I?) (D l2 Station I F- r 15 AMJJASON Station 2 F AMJJASON Station 3 P A.MJJASON Month Station 4 i2" Station 5 [2(- AMJJASON Station 6 lb- AMJJASON Month 16 The round whitefish feeds almost exclusively on benthic organisms and fish eggs, as will be explained in depth in a later section of this paper. AGE AND GROWTH Total Length-Standard Length RelatIOnship A sample of 231 round whitefish was selected from the 370 fish which had both their total and standard lengths measured and the mathematical relationship between these lengths was calculated. When it became apparent that there was no difference between the sexes in this length relationship, the total lengths for both sexes were com- bined and divided by their respective standard lengths to give the following average relationships: Total Length = 1.173 Standard Length ,for fish less than 270 mm in standard length and Total Length = 1.178 Standard Length for fish greater than 270 mm in standard length. Because only four fish shorter than 270 mm in standard lengths were caught, the first equation may not be very reliable. The only other reported total length-standard length relationship is for fish of Moosehead Lake, Maine (Cooper and Fuller, 1945) and was reported as: 17 .OprlmJ>FJH I I Ht- QJh FJN u>p lk)mtoh)mt4l I I Total No. Caught 3 48 125 97 18 O 0 * The 1-inch stretched mesh gill nets were only fished from July 27, 1972 through November 15, 1972. largest, fastest growing young-of-the-year while the 2-inch mesh caught the largest two-year-olds and the smallest three-year—olds. Selectivity of gill nets in the capture of round whitefish is substantiated by Berst (1961) and Normandeau (op. cit.). The fact that there has been no mention of size or age segregation in round whitefish also leads to the conclusion that the gill nets in this 21 study were very selective as to the size of the fish caught. The strong predominance of age-group III individuals over older fish probably reflects conditions in the stock and not gear selection. Table 2 shows that all mesh sizes above l-inch overlapped with respect to their sizes of maximum efficiency and therefore sampled the larger fish in the population more efficiently. The length overlap of various age-groups was fairly large (Table 1). Age-groups III and IV overlapped each other by 80 mm, but this overlap is only based upon two fish--a fast growing member of age-group III and a slow growing member of age-group IV. Only two size ranges con- tained fish of more than two age-groups; the interval from 420-439 mm contained members of age-groups III, IV and V and the interval from 440-459 mm contained members of age-groups IV, V and VI. As the fish get older, they have a smaller size range than the younger fish. This may reflect a trend toward compensatory growth--fish which grow slower than average in their early years may grow faster than average in their later years (Deason and Hile, op. cit.). Natural mortality reduces the number of older fish and for this reason alone there may be less of a size range in the older fish. 22 Further comments on average lengths of age-groups will be discussed with more extensive data in a later section on calculated growth. Body-Scale Relationship To estimate the length of a fish at the time of previous annuli formation, a regression must be calculated between the length of each fish and the length of its scale radius. This regression yields the following pre- diction equation for the body-scale relationship of most fish: TL = a + b(SR) where TL is the total length of the fish (in millimeters here), a is equal to the "Y" or total length intercept of the regression line when the scale radius equals zero, "b" is equal to the slope of the regression line and SR is the magnified scale radius (magnified 22 times and measured in millimeters in this study). Although the "a" value or total length intercept of this prediction equation is often interpreted as the "length at which the fish first formed scales," this inter- pretation is not necessarily correct (Carlander, 1969). Early growth of the scale usually is not prOportional to that of the body even though the scale growth may be pro- portional through much of the fish's life. The value "a" 23 is actually the intercept that will give the best straight line relationship between the fish's length and scale radius. For some fish, the relationship between length and scale radius is not linear at all, but is curved or "S"-shaped (Ricker, 1971). In the present study there were very many large fish (97% of all fish caught were longer than 300 mm in total length) and few small fish. To find what effect this skewed distribution had on the prediction or regression equation of the body-scale relationship, several equations were derived by fitting straight lines to parts of the data with the aid of a CDC 6500 computer and the least squares procedure. The following equations were derived: TL 57.67 + 4.48(SR) derived from 25 fish less than 350 mm in total length TL 92.87 + 3.81(SR) derived from 50 fish less than 370 mm in total length TL 132.60 + 3.44(SR) derived from 233 fish of various lengths, the vast majority being greater than 380 mm in total length TL 303.70 + 1.52(SR) derived from 118 fish all ' greater than 400 mm in total length. These equations differ from one another so markedly because of the tendency for the scale radii to vary quite widely for any given length of fish. In general, those samples which contained larger fish showed smaller slopes and elevated intercept values. 24 Because the regression equations were so affected by the many large fish and the variability of scale radii, an averaging procedure was attempted. The mean total length of all fish in each ten-millimeter length increment was regressed against the mean anterior radius of the scales of these fish and a line was fitted to these data by the least squares method. This averaging method had previously been used by Parsons (1950) and Bailey (op. cit.). The equation obtained by regressing these averages was: TL = 46.49 + 4.58(SR) The correlation coefficient, r, for this equation was .995, a very high correlation. Bailey (op. cit.) found an "a" value of 28 mm for the round whitefish of western Lake Superior. The body- scale equation found by Bailey was: L = 1.10 + 0.05(S) where L is the total length of the fish in inches and S is the scale diameter (magnified 43 times) in millimeters. Mraz (op. cit.) also used Bailey's "a" value for his study of the round whitefish in northern Lake Michigan. No other a values have been reported. No difference was found between the body-scale relationships of the two sexes. Therefore, sexes were combined in finding the body-scale relationship in this study as they were by Bailey (op. cit.) and Mraz (op. cit.) . 25 Calculated Length at Each Annulus The lengths of each fish at the time each of its annuli was formed were back calculated using a nomograph based upon the relationship derived by Fraser (1916). Fraser developed a formula for calculating the previous growth of a fish based on the assumption that body growth is directly related to the prOportional growth of the scale and not to the absolute size of the scale. Following this assumption, the following equation is used to calculate body length at an earlier age: (LT - A) Ln = a + ———§————~ S T n where Ln is the calculated total length of the fish at the end of n years, "a" is the Y or total length intercept of the body-scale relationship regression, L is the total T length of the fish at capture, Sn is the length of the scale radius from the focus to the "nth" annulus, and S is T the length of the radius from the focus to the anterior margin of the scale. The back calculated lengths were determined separately for males and females and the females were found to average from two to four millimeters longer than the males in total length. Neth (1955) also found that females were slightly longer than males but Bailey (op. cit.) found no difference in length between the sexes. The length 26 differences in the present study proved to be non- significant when tested with a Student's "t" test at the one percent level. Therefore, the back calculations for both sexes were combined and are presented in Table 3. Table 3 represents the back calculated lengths for the 233 fish caught between September 8, 1972 and November 15, 1972. As previously stated, these fish were chosen because they were caught in a relatively short period of time during which growth had either completely or nearly stopped for the year. The calculated lengths for the various age-groups show no evidence of "Lee's phenomenon" of a progressive decrease in the estimate of length at the end of a particular year of life with increase in the age of the fish from whose scale the estimate was made. On the con- trary, the trend which exists is towards a progressive increase in calculated length with an increase in age. This trend becomes most apparent after the second year of life and persists through the fifth and sixth years. Mraz (op. cit.) also found an apparent reversal of Lee's phenomenon for Lake Michigan round whitefish while Bailey (op. cit.) found Lee's phenomenon to apply to Lake Superior round whitefish. Possible explanations for the apparent increase in calcualted length with an increase in age are: size 27 om om am we om mad mma rumcmq mo pamEOHOCH ommno>< ccmuw am an OS om Hm SHH mmH mmmum>4 mo acosmuocH awe owe ome Sam mam mmm mma mmmum>¢ wanna awe How Ame new mom mom nma H mmv HH> I owe owe mow Hem Ohm med ma mew H> I I emv oov mmm mmm mma mm omv > I I I amm mam 5mm sea mm maw >H I I I I nmm new «ma mm mmm HHH I I I I I new mma ma Hmm HH I I I I I I one H onm H I I I I I I I m SSH o onsummu A o m a m m H um zmflm mesoq msouu mo .02 HONOR ova AEEV COHDOEHOM mSHsccd nomm um zumcoq HOMOB ommum>¢ .cmmHQOHz mxmq Hmuusoo EOHM cmflmouwg3 canon mo OMHH Mo “mom some mo cam ecu um numcoa Hmuou poumHDOHMUII.m mqmfie 28 selective mortality that bears more heavily on the smaller fish of an age-group, non-random sampling (catching the faster growing fish), a failure of the body-scale relation- ship to fully explain the real relationship between the growth of a fish and its scales throughout the fish's life or changing environmental conditions within the body of water studied. The two estimates of growth in length from Table 3-- the grand average increments of length and the length increments based on average length in successive ages-- gave almost identical descriptions of growth through the first four years of life. Because the grand average incre- ments of length are not influenced by fish which have not completed the current year's growing season, these incre- ments give the best description of actual growth and are used to describe the absolute and incremental growth of the round whitefish in Figure 3. Maximum growth in length of the round whitefish occurred during the first year of life and remained high during the second and thrid years of life. From a maximum growth in length of 139 mm in the first year of life, the calculated annual growth increment declined to 20 mm in the seventh year of life. Table 4 indicates that the average calculated lengths of the fish in this study are the greatest that 29 Figure 3.--Average absolute and incremental growth in length for 233 round whitefish from central Lake Michigan. 30 AEEV foam. 5 . £396 BEmEmtoc. 0 w 1 O 5 _ -i I00 Absolute growth Incremental growth _ IOO — T _ _ _ O O O O O O O O 5 4 3 2 8:252 335.6 6 AEEV :35. .20... Age (annuli present) 31 I I I I I awe owe wmv mam mam mmm mma cmmwnOHz mxmq Hmuucou I I I I was New ASS mam Hem «Hm mam AHA A.AAo .mo .Nmnzv smmflnOHz mxmq suonunoz I I I can mhm mmm mmm pom «hm Hmm mmH baa A.ufio .mo .moaflmmv HOAHOmsm mxmq UnmamH Oflumomm mme nmv Haw mmm Hmm mmm mmm mom mom mam NmH om A.OHO .mo .woaflmmv Hofluomsm Oxmq mammom OHmH I I NNS mom mmm kmm emm I I I I I A.AA6 .mo .somccmmv oxmq Hmom umono NH Ha 0H m m h o m e m m H oxen AEEV soflpmfiuom msHscs< um numcmq Hmuoa pcsou mo .mmxma cmoanmfid suuoz Eoum cmflmoufl33 cofiumEHom unasscm some um mnumcma Hmuou cmumasoamo ommuo>4ll.v mamme 32 have been reported. This table also shows that there is a definite trend of increasing length for a specific year of life in the more "southern" waters. Great Bear Lake (Kennedy, 1949) is located on the Arctic Circle and the fish from this lake have the slowest growth rate. The present study is the farthest south of any yet reported and these fish attained the greatest growth in length per year of life. The more southern waters have longer growing seasons and are somewhat more eutrOphic. As will be examined in later sections of this paper, the southern- most fish are the heaviest for any specific age, are the shortest lived and mature at the earliest age. LENGTH-WEIGHT RELATIONSHIP AND CONDITION Length-Weight Relationship The length-weight relationship describes mathe- matically the relationship between length and weight, primarily so that one may be converted into the other and so that comparisons may be made between populations. In fish with constant form and Specific gravity, the length- weight relationship can be represented by W = aLb where W is the weight in grams, "a" is a constant, "b" is an exponent with a value nearly always between 2 and 4, and L is the total length in millimeters. A value of "b" equal to 3 indicates that the fish grows symmetrically or isometrically (provided its specific gravity remains con- stant). Values other than 3 indicate allometric growth; if "b" is greater than 3, the fish becomes "heavier for its length" (Ricker, 1971) as it grows larger. The above length-weight relationship may be converted into a linear relationship by a logarithmic transformation into the following: 33 34 Log W = Log a + b(Log L) The coefficients in this equation may vary with sex or sexual maturity, season of the year or time of day (because of changes in stomach fullness). In this study the length-weight relationship was examined for each sex and for three "seasons" of the year--spring, April 1- June 15; summer, June 16-August 31; and fall, September 1- November 15. The length-weight relationships were calculated by the method of least squares by a CDC 6500 computer. The females weighed slightly more than the males at all well represented lengths, but because the differences were not statistically significant, the following length-weight regression equations represent the sexes combined for each season: Spring Log W -5.5205 + 3.1629(Log L) Summer Log W -6.4211 + 3.5235(Log L) Fall Log W -6.3392 + 3.4849(Log L) These equations represent only mature fish taken through- out the sampling periods. There is no significant difference between the summer and fall length-weight relationships but there is a difference between the summer-fall relationships and the spring relationship. This is to be expected because a fish would weigh the least at a given length immediately 35 after overwintering and before the gonads begin their yearly development. These prediction equations give very close agreement between the actual and computed weights for fish of a given total length (Table 5). TABLE 5.--Average calculated and empirical weights for each age-group of round whitefish caught from September 1, 1972 through November 15, 1972 in central Lake Michigan. Average Average Age- Total Length Empirical Calculated Group* at Capture Weight Weight (mm) (gm) (gm) 0 144 19 15 I 270 130 127 II 331 260 277 III 383 457 454 IV 419 633 629 V 450 795 801 VI 475 985 975 VII 495 1165 1130 * Because these fish were collected at or near the end of the growing season, the lengths and weights given are approximately the maximum attained by each age-group. Figure 4 graphically illustrates the calculated growth in the weight of round whitefish from central Lake Michigan. 36 Figure 4.--The average length-weight relationship for 233 round whitefish from central Lake Michigan. The curve represents the calculated weights and the dots, the empirical weights. |200 IOOO 800 Weight (gm) 400 200 IOO 37 l l l 200 300 y 400 Total' Length (mm) J 500 38 Bailey (op. cit.) and Mraz (op. cit.) have reported length-weight relationships from fish taken in gill nets in Lake Superior and Lake Michigan. Bailey found the average length-weight relationship for Lake Superior round whitefish for the entire year to be Log W = -5.276 + 3.223(Log L) where w is the weight in grams and L is the total length in millimeters. Mraz found the length-weight relationship immediately after spawning in northern Lake Michigan to be Log W = -4.695 + 3.294(Log L) To compare average weights for given lengths or ages, the length-weight equations of various populations may be compared. However, since the reported equations have slightly different slope and intercept values, the average calculated weight at each year of life may show differences more clearly (Table 6). It is apparent from Table 6 that the fish from the present study weight the most for any given age. By comparing Table 4 and Table 6 it is also apparent that fish from the present study generally weight the most for any given length. However, because each of the tabulated studies was carried out at a slightly different time of year, Table 6 should merely be interpreted as showing increasing weight for fish of a given age and length in the more "southern" waters. 39 .mcflumm on» ma QOAAMEHOM msHsssm um anon» 3OHOQ maucmflam on woe munmwmz Omega OHOMOHO£N .sOHumEHOm flasscm poumfia may on HOAHQ new» on» no Hamm may ca pogomaaoo mums swam savage“: oxmq Hmuucoo was * I I I I omHH mAm How amm Sma AAA AAA ma «ammflnoflz mxmq HMHflflmu I I I I owe mHA Ham Ame cam cam SA AH A.AAo .eo .Nmuzv confiscaz Oxmq CHOSuHOZ I I I MAS mmv Amm Sam «mm mma mm ms HA l.aAo .mo .AmAAmmv Hoauomsm oxoq camamH mapmom< com MOA Ase mam SAS Ham mom SAN mma mm mm mo A.DAo .mo .Amaflmmv Hofluomsm oxmq Homom OHmH I I mom oam Sme mam mam I I I I I x.aAo .mo .Acmccmmc Oxmq Hmmm “mono NH AH OH a m A m ‘ m a m m A AEmV coaumEHom nuanced um unmwoz mxmq .moxmq cocauofis sunoz Scum swam IOOHQB canon mo coflwmeuom mSHDccm name no mpsmwm3 covmasoamo ommnm>aII.o mamas 40 Condition The coefficient of condition, K, is defined as being an index of the general "well being" or "plumpness" of fish. This index is often calculated as a means of comparing fish from various areas or evaluating the effectiveness of various management programs. The coefficient of condition may be affected by the age or sex of the fish as well as by the time of year in which the fish is captured. Table 7 lists the "K" values for the round whitefish which were derived by the formula: _ W x 10 TL TL3 where KTL is the condition factor based on the total length, W is the weight in grams and TL is the total length in millimeters. Several trends are readily observed from Table 7. The condition factor was lowest in the spring and highest in the summer. This trend agrees with other round white- fish studies. Although no specific figures are given, Mraz (Op. cit.) stated that the round whitefish in northern Lake Michigan reach maximum condition in early fall and decline during the winter. Bailey (op. cit.) suspected that round whitefish reach peak condition in August, as has been established for such other coregonids as 41 TABLE 7.--Average condition of the round whitefish of central Lake Michigan for each age and season of the year. Average Condition for Each Season Sex Age Spring Summer Fall Males 2 - .7767 .7423 3 .7745 .8276 .8258 4 .7966 .8542 .8744 5 .8278 .9324 .8748 6 .7737 .9211 .9576 7 _ _ _ Grand Average: .7865 .8790 .8588 Females 2 .6806 - .7644 3 .8037 .8607 .8601 4 .7698 .8613 .8859 5 .7867 . .9296 .9169 6 .7893 .9466 .9545 7 - 1.0530 .9903 Grand Average: .7809 .8836 .8803 Leucichthys kiyi (Deason and Hile, op. cit.) and Coregonus clupeaformis (Van Oosten and Hile, op. cit.). The decrease in condition in the late fall may be partially due to the decrease in feeding as the spawning season approaches. The present study showed that 25 per- cent of the stomachs examined were empty in the fall 42 period as compared to 6 percent in the spring and 13 per- cent in the summer. Normandeau (op. cit.) found that most round whitefish stomachs examined just prior to and during the spawning period were empty. Other obvious trends in the condition of the round whitefish are an increase in condition with an increase in age and a higher condition coefficient for females than for males in the summer and fall. The lower condition of the females in the spring may be linked to the spent con- dition of their gonads. The only mention of a specific condition value in the round whitefish literature is one for both sexes combined in the fall of the year at Little Moose Lake, New York (Neth, op. cit.). This K value of .8066 compares TL to a KTL value for both sexes in the fall in this study of .8588. The higher K value in the present study is TL understandable because of the high growth rate of central Lake Michigan round whitefish. SEX RATIO AND MATURITY Sex Ratio A total of 370 round whitefish were caught through- Iout this study. Of this total, 160 were females, 195 were males and the sex could not be determined on the remaining 15. A chi-square determination showed that the total number of fish of each sex caught was not significantly different from a 1:1 sex ratio at the one percent level. However, significantly more males were taken in the fall. This increase was due to the fact that males usually arrive at the spawning grounds before the females (Normandeau, op. cit.). Male round whitefish slightly outnumbered females in age-groups II-V, while females were slightly more plentiful in age group VI and both of the age-group VII fish caught were females. However, none of these differ- ences in sex per age-group was judged significant at the one percent level by a chi-square test. A larger sample size may have yielded some significance. Bailey (op. cit.) noted that female round whitefish became progressively more plentiful in age-groups VI through IX in Lake Superior. Kennedy (op. cit.) also found a predominance of females in all age-groups greater than VIII in Great Bear Lake. 43 44 Maturity Mature round whitefish were defined as fish which would spawn in the fall of the year of this study, regard- less of whether or not they had previously spawned. The sex and state of maturity were determined by gross examina- tion of the gonads. The youngest mature fish of both sexes belonged to age-group II and approximately fifty percent of these fish were mature. Approximately ninety percent of the age- group III fish were mature and all fish of age-groups IV and older were mature. A chi-square test showed no sig- nificant difference between the percentages of mature males and females. Farther north in Lake Michigan, Mraz (op. cit.) found thirty-six percent of the age-group II males but none of the females were mature and all fish beyond age-group III were mature. In Lake Superior, Bailey (op. cit.) found that the youngest mature fish of both sexes belonged to age-group II. However, all males were not mature until age V and all females were mature at age VI. Kennedy (op. cit.) found that in Great Bear Lake only eighty-eight percent of the round whitefish in age-group IX were mature. These differences in age at maturity can most probably be explained by the large differences in growth rates in these lakes. Also, since none of the aforementioned 45 authors defined maturity, it can only be assumed that maturity was defined in terms of when the fish would spawn as opposed to merely the age at which the sex of the fish could be determined. FOOD HABITS Qualitative and quantitative studies of the food habits of the round whitefish are nearly non-existent. The majority of authors merely state the "main" food item or items in the diet. Koelz (op. cit.) stated that round whitefish feed upon Gastropoda (snails), Tricoptera (caddis flies) and Ephemeroptera (mayflies) in Lake Huron. Kennedy (op. cit.) found that the main food items in Great Bear Lake included all of the above and also Chironomidae (midges). Rawson (1951) stated that Gastropoda and Tricoptera were the predominant items eaten in Great Slave Lake. The only previous detailed study of the food of the round whitefish is an analysis of 146 fish from western Lake Superior (Anderson and Smith, 1971). In the present study of central Lake Michigan round whitefish, 337 fish stomachs were collected over an eight-month period. This period was broken into three 75-day periods in an attempt to roughly approximate spring, summer and fall as previously defined. All of the fish were caught by gill nets at the established sampling stations. No regurgitation by the round whitefish in the nets was ever noted. 46 47 The stomachs, defined as the intestinal tract from the foremost part of the esophagus to the pyloric sphincter, were removed from the freshly caught fish and preserved in ten percent formalin. The stomach contents were later analyzed by identifying the food items present to the lowest taxonomic group possible and counting all items. The total volume of each type of food item present was measured by water displacement using a graduated centri- fuge tube and measuring to the nearest .05 milliliter. The groups of food organisms found are listed in Table 8. Methods of Food Analysis In their study of round whitefish food habits of western Lake Superior, Anderson and Smith (op. cit.) divided the round whitefish into two groups: those less than 254 mm in total length and those greater than 254 mm in total length. In the present study, only four fish less than 254 mm in total length were captured and their food was no different from that of the larger fish. For this reason, the food of the round whitefish was analyzed on a seasonal basis, without regard to size of the fish. The stomach contents were expressed by percent frequency of occurrence, percent of the total volume of all food items eaten and percent of the total number of all food items eaten. These percentages reflect only stomachs which contained food. Hynes (1950) reviews these and other MAE? w” I -' ‘ljftm‘nr'ohfinpq‘? E: I. ‘h 48 TABLE 8.—-Food items eaten by round whitefish in central Lake Michigan between April 1, 1972 and November 15, 1972. Mollusca GastrOpoda Physidae Physa sp. Pleuroceridae Pleurocera sp. Planorbidae Helisoma sp. Lymnaeidae L naea sp. Ancylidae Ferrissia sp. Pelecypoda Spheriidae Arthropoda Insecta Diptera Chironomidae - larvae Tricoptera Phryganeidae Phryganea sp. - nymphs Leptoceridae - nymphs Limnephilidae - nymphs Beraeidae - nymphs Ephemeroptera Heptageniidae - nymphs PleCOptera Perlodidae - nymphs Coleoptera - adults Hemiptera - adults Eucrustacea Cladocera Amphipoda Pontoporeia affinis Isopoda Lirceus sp. Decapoda Arachnoidea Hydracarina Annelida Hirudinea Chordata Osteichthyes - fish eggs 49 methods of food analysis in great depth but a brief discussion of the methods used here is warranted. The "frequency of occurrence" method of food analysis consists of recording the number of stomachs in which each food item occurs and expressing this number as a percentage of the total number of stomachs examined. This method alone demonstrates what organisms are being fed upon, but it gives no information on the total numbers of the specific items eaten nor on the volume or size of these items. The "percent of the total volume of all food items" method consists of measuring the total volume for each type of item found and expressing these item volumes as a percentage of the total volume of food in the entire series of fish stomachs examined. This method emphasizes the importance of large food items. However, volumetric studies alone tend to mask the importance of the smaller food items. The data may also be distorted by the occasional occurrence of an exceptionally bulky food item or by differential rates of digestion of different items. Although problems due to differential rates of digestion were anticipated, very little material in the round whitefish stomachs was unidentifiable. There appear to be several reasons for this. The water temperatures were usually quite cold, below 10°C on seventy-five percent of the sampling days. All fish were placed on ice 50 immediately after capture. Equally important was the fact that the gill nets were set at dawn for twenty-four hour periods and all of the fish were removed from the nets as soon after dawn of the following day as possible. Hart (1931) found that round whitefish were captured in much greater numbers at night than during the day. Therefore, the majority of round whitefish caught in the gill nets had probably been caught in the preceding few hours and little digestion had occurred. The percentage which each food item contributes to the total number of items eaten is often called the "numerical" methods of food analysis. This method gives the percent representation, by number, of each type of food item eaten. However, this method alone gives no information on how frequently an item is eaten nor on the item's volume or size in relation to other items. Although each of the above methods of food analysis has its limitations, the three methods together give a good indication of the overall importance of the various food items in the diet. The seasonal variation of the food of the round whitefish in central Lake Michigan is shown graphically in Figures 5, 6 and 7. The seasonal percent frequency of occurrence of individual food items are listed in Table 9. 51 Figure 5.--Spring food habits of the round whitefish in central Lake Michigan. The upper pie graph illustrates the percentage which each item contributes to the total number of food items eaten. The lower graph illustrates the per- centage which each item contributes to the total volume of food items eaten. Items less than one percent of either total number or total volume are not included. 52 SPRING FOOD HABITS (April I - June l5) Chironomids (89.8%) MISC. 0.6%) - Moyflies (|.l%) ‘ AmphipodsIl.7%) Snails (|.7%) Isopods (41%) Percent of total number Chironomids (6|.3%) Crayfish ( 2.6%) \‘ Moyflies (2.8%) Tricoptera (3.7%) Leeches (22.2%) ' Snails (3.7%) Isopods ( 3.3%) Percent of total volume 53 Figure 6.--Summer food habits of the round whitefish in central Lake Michigan. The upper pie graph illustrates the percentage which each item contributes to the total number of food items eaten. The lower graph illustrates the per- centage which each item contributes to the total volume of food items eaten. Items less than one percent of either total number or total volume are not included. 54 SUMMER FOOD HABITS (June I6 - August .3” Chironomids (49.9%) Tricopte ro ( t.3%) Clams ( l.4%) Snails ( 20.0%) Cladocerans (5.6%) Fish eggs (2|.2%) Percent of total number Chtro nomids ((5.2%) Crayfish ( 25.6%) icopte ro (5.0%) Snails (43.8%») Percent of total volume 55 Figure 7.--Fall food habits of the round whitefish in central Lake Michigan. The upper pie graph illustrates the percentage which each item contributes to the total number of food items eaten. The lower graph illustrates the percentage which each item contributes to the total volume of food items eaten. Items less than one percent of either total number or total volume are not included. 56 FALL FOOD HABITS (September I- November I5) Chironomids (83.4% I Fish eggs +I I.5%) Snoi Is ( l4. 4%) Percent of total number Chironomids (39.6%) Snails ( 33.5%) Crayfish (7.2%) Tricoptera (3. 8%) Percent of total volume 57 TABLE 9.--Seasonal percent frequency of occurrence of food items present in round whitefish stomachs of central Lake Michigan. Seasonal Percent Frequency of Occurrence* Food Item Spring Summer Fall Chironomidae 88.1 55.7 57.3 Gastropoda Snails 22.6 75.6 52.0 Limpets 0.0 0.0 2.7 Tricoptera 14.3 19.5 8.0 Hirudinea 19.0 0.0 1.3 Decapoda Crayfish 6.0 14.6 14.0 Amphipoda 19.0 2.4 0.7 ISOpoda 15.4 7.3 0.0 Ephemeroptera 11.9 4.9 2.0 'Fish eggs 2.1 24.4 15.3 Cladocerans 0.0 9.8 0.7 Pelecypoda 7.1 17.1 2.0 PleCOptera 2.1 0.0 0.0 Hydracarina 0.0 7.3 0.0 Misc. insects 10.7 6.1 2.0 Unidentifiable Material 20.3 14.6 3.3 Sand 38.1 34.2 . 35.3 * Empty stomachs were not included in calculating the seasonal percent frequency of occurrence. In the spring period, 5 of 89 stomachs (6%) were empty, 6 of 47 stomachs (13%) were empty in the summer and 51 of 201 stomachs (25%) were empty in the fall. 58 Analysis of Food Habits During the spring season (April l-June 15) Chironomidae were by far the most abundant food item eaten, making up 90 percent of the total number of all food items. Chironomids also made up 61 percent of the total volume of food items eaten during the spring while Hirudinea (leeches)made up 22 percent of the total volume. Leeches occurred in very small numbers but had a consider- able collective volume. Spring was the only season in which leeches made up a significant part of the diet. The lesser contributors (making up between one and four percent of either the total number or total volume of food items) to the diet during the spring were: GastrOpoda, Tricoptera, IsopOda, Amphipoda, Decapoda (crayfish) and Ephemeroptera. Chironomids made up fifty percent of the total number of food items found during the summer (June 16- August 31), while fish eggs, gastropods, and Cladocerans also contributed significantly. The volumes of the major summer foods gives quite a different picture. Gastropods made up forty-four percent of the total volume of items eaten while crayfish, Chironomids, fish eggs and Tricoptera made up smaller percentages. During the fall season (September l-November 15) Chironomids were once again the most abundant food item eaten (83% of the total number), while gastropods and fish eggs were eaten in lesser but significant numbers. However, 59 as a percent of the total volume, Chironomids made up only forty percent while gastropods contributed thirty-four percent. Fish eggs, crayfish and Tricoptera made up the remainder of the total volume. The food items and their respective habitats, as described by Pennak (1953), and the fact that the round whitefish has a small inferior mouth, clearly indicate that the round whitefish is a bottom feeder. This is further supported by the fact that sand occurred in one- third of the stomachs containing food (Table 9). Some speculations on the seasonal food variations are in order. Chironomids were most plentiful in the spring before many had emerged. Because of pupation and emergence the number of Chironomids was reduced in the summer and this, together with more small snails and crayfish being available, led to an increase in the numbers and volumes of snails and crayfish eaten. Spottail shiners (Notropis hudsonius), slimy sculpins (Cottus cognatus) and ninespine sticklebacks (Pungitius pungitius), all indigenous to the area, spawn during the summer season and their eggs were utilized as food. In the fall larger numbers of Chironomids were available again (although their volume per individual was less than in the spring), while the crayfish and snails were becoming larger and therefore less available as food. Lake trout spawning in the sampling area were the source of the eggs in the fall diet. 60 The large volume of leeches in the spring season is puzzling but may be explained by a possible swarming or schooling of leeches. Most of the fish which contained leeches contained several of them. Anderson and Smith (op. cit.) examined 63 full stomachs of large (greater than 254 mm) round whitefish from western Lake Superior. They found the diet in E ‘4 February made mainly of Isopods (62% of the total volume), I I Tricoptera (15%) and Hirudinea (7%). The summer season was represented by one fish which had eaten 100 percent Tricoptera. The fall diet was composed of mainly Mysidacea, coregonid eggs, gastropods and unidentifiable material (percentages of total volume not available). Anderson and Smith (op. cit.) examining 69 full stomachs, found that fish less than 254 mm in length fed upon Chironomids (22% of the total volume), Plecoptera (27%), Mysidacea (10%) and COpepods (10%) in May. In the summer months the major items in order of volume were Cladocerans, copepods, Plecoptera and Chironomids. The fall food was mainly made up of Chironomids, Mysidacea, copepods and Cladocerans (percentages of total volumes were not available for the summer or fall seasons). An attempt was made to examine food selectivity by the round whitefish. Over the eight month sampling period eighteen Ponar dredge samples were taken at each sampling 61 station. However, these samples yielded only six animal groups--Oligochaeta, Gastropoda, Pelecypoda, Hydracarina, Amphipoda and Chironomidae.- Any attempt to show selectivity or electivity (Ivlev, 1961) would have yielded one hundred percent selectivity for several of the food items in the round whitefish stomachs. The benthic sampling procedures were simply not adequate to give a true representation of the benthic organisms present. In the future, artificial substrate devices will be used to sample benthic organisms in the study area and a selectivity index may then be possible. Because of the present lack of adequate benthic sampling techniques in the sampling area, this food study gives the most complete picture of the benthic organisms present in the area. Any major change in the food habits of the round whitefish in the area of the Ludington pumped storage plant in the near future may indicate a change in the aquatic environment and in the benthic community of the area. .e. . 1 a A." . a )q‘I ‘0 I‘I‘I S UMMA RY This study was undertaken to update age and growth information for the round whitefish in Lake Michigan and to investigate seasonal variations in the food of the round whitefish. It is also hOped that the age, growth and food relationships gained from this study will allow the round whitefish to become a biological indicator of possible ecological changes in Lake Michigan, near Ludington, Michigan. During an eight month period of gill net collec- tions, 370 round whitefish were caught. The 233 fish caught between September 8, 1972 and November 15, 1972 were analyzed in an age and growth study. Food habits of 337 fish captured over the entire collection period were analyzed. The total length-standard length relationship was determined to be: Total Length = 1.178 Standard Length for fish longer than 270 millimeters in standard length. The majority of fish caught were three and four year-olds. Few fish younger than three years old were 62 63 taken because of either gear selectivity or an absence of these fish from the area. The body-scale relationship, determined by a linear regression of average body length on average scale radius length, was: TL = 46.49 + 4.58(SR) This equation permitted the calculation of the length of the fish at the time of each annulus formation. A reversal of "Lee's phenomenon" was noted as has been noted for several other coregonids. Possible explanations for this phenomenon include size selective mortality, non-random sampling, a change in the body- scale relationship at some point of the fish's life or changing environmental conditions in the body of water studied. Length-weight relationships were derived for each season of the year: Spring Log W -5.5205 + 3.1629(Log TL) Summer Log W -6.4211 + 3.5235(Log TL) Fall Log W -6.3392 + 3.4849(Log TL) The fall equation was tested on fish caught in the fall and the calculated weights were very close to the empiri- cal weights. 64 The condition factor, K was highest in the TL' summer and lowest in the spring. Females had the higher condition in the summer and fall while males were higher in the spring. An increase in condition with age was also noted. Females were found to generally be slightly longer . and heavier than males. The sex ratio caught over the g sampling period was 1:1. Approximately fifty percent of the two year old fish and ninety percent of the three 7'» year old fish were mature. E The round whitefish of central Lake Michigan were found to be the fastest growing of any population of round whitefish yet studied. The fish in this study had the greatest average total length for every year of life and the greatest weight for most lengths. Fish from more northern localities grew slower, matured later and lived longer. The major food items of round whitefish in central Lake Michigan were aquatic insects, with Chironomidae being by far the most important. Hirudinea, Mollusca, Decapoda and fish eggs were also very important food items. In the spring Chironomids made up ninety percent of the total number of food items eaten but only accounted for sixty-one percent of the total volume. Hirudinea accounted for less than one percent of the total number of food items eaten total volume of all Chironomids eaten in the summer 65 but made up twenty-two percent of the items eaten. made up fifty percent of the food items with twenty-one percent contributed by fish eggs and twenty percent from snails. These organisms contribute quite different prOportions of the total volume items eaten. Forty- four percent of the total volume con- sisted of snails while twenty-six percent came from cray- fish, fifteen percent from Chironomids and ten percent from fish eggs. In the fall Chironomids continued to be the major food item by number, making up eighty-three percent of the total number of items eaten, while snails contributed fourteen percent. Chironomids made up a much smaller pro- portion of the total volume of foods eaten, accounting for forty percent, while snails made up thirty-four percent, crayfish added sixteen percent and fish eggs contributed seven percent. w- “mm LITERATURE CITED 66 LITERATURE CITED Anderson, E. D. and L. L. Smith. 1971. A synoptic study of food species from western Lake Superior. Univ. of Minn. Ag. Experiment Station, Tech. Bull. No. 279. 199 pp. Bailey, M. M. 1963. Age, growth and maturity of round whitefish of the Apostle Islands and Isle Royale regions, Lake Superior. Fish. Bull. U. S. Fish and Wildlife Service, 63(1):63-75. Baldwin, N. S. and R. W. Saalfeld. 1962. Commercial fish production in the Great Lakes 1867-1960. Great Lakes Fish. Comm. Tech. Rept. 3. 166 pp. Berst, A. H. 1961. Selectivity and efficiency of experi- mental gill nets in South Bay and Georgian Bay of Lake Huron. Trans. Am. Fish. Soc. 90:413-418. Carlander, K. D. 1969. Handbook of freshwater fishery ' biology, Vol. 1. Iowa State University Press, Ames, Iowa. 752 pp. Cooper, G. P. and J. L. Fuller. 1945. A biological survey of Moosehead Lake and Haymock Lake. Maine Dept. Int. Fish and Game Fish Surv. Rep. 6:1-160. Deason, H. J. and R. Hile. 1947. Age and growth of the kiyi, Leucichthys coulteri, in Lake Superior. Trans. Am. Fish. 800. 74:88-142. Fraser, C. McL. 1916. Growth of the Spring Salmon. Trans. Pacif. Fish. Soc. Seattle, for 1915, pp. 29-39. Hart, J. L. 1931. On the daily movements of the Coregonine fishes. Canadian Field-Nat. 45:8-9. Hile, R. 1936. Age and growth of cisco, Leucichthys artedi (Le Sueur), in the lakes of the north- eastern highlands, Wisconsin. Bull. U.S. Bur. of Fish, 48:211-317. 67 68 Hynes, H. B. N. 1950. The food of freshwater sticklebacks (Gasterosteus aculeatus and Pygosteus pungitius), with a reveiw of methods used In studies of the food of fishes. J. Anim. Ecol. 19:36-58. ‘Ivlev, V. S. 1961. Experimental ecology of the feeding of fishes. Yale University Press, Clinton, Mass. 302 pp. Keeton E. 1965. Application of Stoeltzner's method to detemine growth of fish scales. Trans. Am. Fish. Soc. 94:93-94. Kennedy, W. A. 1949. Some observations on the coregonine fish of Great Bear Lake, NWT. Bull. Fish. Res. Ed. Can., No. 82. 10 pp. Koelz, W. 1929. Coregonid fishes of the Great Lakes. Bull. U.S. Bur. Fish., 43(1927), Pt. 2, 297-643. Lyles, C. H. 1969._ Fisheries statistics of the United States. U.S. Fish and Wildlife Service, Bureau of Commercial Fisheries. 474 pp. McHugh, J. L. 1941. Growth of the Rocky Mountain Whitefish. J. Fish. Res. Ed. Can. 5(4):337-343. McPhail, J. D. and C. C. Lindsey. 1970. Freshwater fishes of northwestern Canada and Alaska. Bull. Fish. Res. Ed. Can. No. 173. Mraz, D. 1964. Age and growth of the round whitefish in Lake Michigan. Trans. Am. Fish. Soc. 93(1):46-52. Neth, P. C. 1955. Assessment of a control program for common whitefish and round whitefish in Little Moose Lake, N.Y. Thesis, Cornell University. Unpublished. Normandeau, D. A. 1969. Life history and ecology of the round whitefish Prosopium cylindraceum (Pallas), of Newfound Lake, BfIStol, New Hampshire. Trans. Am. Fish. Soc. 98:7-13. Parsons, J. W. 1950. Life history of the yellow perch, Perca flavescens (Mitchill), of Clear Lake, Iowa. Iowa State College Journal of Science, 25:83-97. Pennak, R. W. 1953. Fresh-water invertebrates of the United States. Ronald Press CO., New York. 769 pp. 69 Rawson, D. S. 1951. Studies of the fish of Great Slave Lake. J. Fish. Res. Ed. Can. 8(4):207-240. Ricker, W. E. 1971. Methods for assessment of fish pro- duction in fresh waters. IBP Handbook No. 3. Willmer Brothers Limited, Birkenhead, Great Britain. 348 pp. Slastenenko, E. P. 1958. The freshwater fishes of Canada. Kiew Printers, Toronto. 385 pp. Smith, S. H. 1954. Method of producing plastic impres- sions of fish scales without using heat. Prog. Fish-Cult. l6(2):75-78). Van Oosten, J. 1923. The whitefishes (Coregonus clupeaformis). A study of the scales of white- fishes of known age. Zoologica, Sci. Cont. of the N.Y. Zool. Soc. 2(17):380-412. and R. Hile. 1949. Age and growth of the lake whitefish, Coregonus clupeaformis (Mitchill), in Lake Erie. Trans. Am. Fish. Soc., 77:178-249. APPENDIX 70 73 APPENDIX TABLE 3.--The number of round whitefish caught per gill net lift at station three. Date Water Temperature (°C)* No. of Fish April 10 April 11 April 17 April 20** April 26 May 8** May 18 May 21 May 22 May 23 June 2 June 5 GOGGOGOWWUTWN OOOI—‘OONUlUII—‘Ibw June 26 6 June 27 9 July 7 8 July 16 16 July 27 9 July 28 6 August 13 11 August 25 19 August 28 19 OOHOOJOOOH September 8 18 September 22 17 October 4 15 November 1 10 November 9 9 November 15 7 UTQDI-‘ONH H * This represents the temperature at the lake bottom at station three - the "fishing" depth. ** On these dates the gill nets were lifted after a 72-hour period rather than the normal 24-hour period. MICHIGAN STRTE UNIV. LIBRARIES 31293106996790