FOOD SELECTION AND FEEDING RELATIONSHIPS 0F YELLOW PERCH PERCA FLAVESCENS (MITCHILL) WHITE BASS 'MORDNE CHRYSOPS (RAHNESQUE); FRESHWATER DRUM APLODINOTUS? GRUNN'IENS (RAFINESQUE) AND GDLDFISH CARASSIUS AURATUS (LINNEAUS) IN WESTERN LAKE ERIE Thesis for the Degree of M. S. MICHIGAN STATE UNIVERSITY DAV! D ELLIS KEMGA 19 7 5. c- 291 w 0.9.0...“ THESIS IIIIIIII IIIIIIIIIIIIIII III 31293 008481917 ET"’an IIIJAG I 800K 8"? EIIY INC. ”LIB“ R BINDF 5 ... ' I It; DEC 06!?” W moan-9s WE ‘I‘. -. I' \"‘\ \ , t ’ w a ‘0‘ a " } r u} - ‘I 4 'I' 4" 'I ' FOOD SELECTION AND FEEDING RELATIONSHIPS OF YELLOW PERCH PERCA FLAVESCENS (MITCHILL), WHITE BASS MORONE CHRYSOPS (RAFINESQUE), FRESHWATER DRUM APLODINOTUS GRUNNIENS (RAFINESQUE) AND GOLDFISH CARASSIUS AURATUS (LINNEAUS) IN WESTERN LAKE ERIE By David Ellis Kenaga 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 1975 ABSTRACT FOOD SELECTION AND FEEDING RELATIONSHIPS OF YELLOW PERCH PERCA FLAVESCENS (MITCHILL), WHITE BASS MORONE CHRYSOPS (RAFINESQUE), FRESHWATER DRUM APLODINOTUS GRUNNIENS (RAFINESQUE) AND GOLDFISH CARASSIUS AURATUS (LINNEAUS) IN WLSTERN LAKE ERIE BY David Ellis Kenaga This study was undertaken as part of an investigation of the impact of once through cooling at a large power plant in Western Lake Erie and is an attempt to assess the relationship among fish based on foods consumed. Potential food organisms and stomach contents of yellow perch, white bass, freshwater drum and goldfish were sampled and compared over a two year period. On the basis of differences in food size alone, young of the year fish did not appear to be in competition but as they became larger, all but goldfish consumed the same mean size foods. Within a fish species, mean prey size varied little in fish older than age class zero. Goldfish differed markedly by lacking the prey size selectivity demonstrated by the other fish species. Perch, drum and white bass preferred large organisms, specifically Leptodora kindtii and Chironomus sp. while goldfish consumed smaller species, particularly cyclopoid copepods. Some ramifications of food size and prey selectivity in relation to trophic dynamics, feeding efficiency, composition and distribution of fish species, and the use of cooling water by large power plants and their possible impact upon prey size were discussed. ACKNOWLEDGMENTS I wish to express my utmost appreciation to the people who have made this study a reality. Especial thanks are in order for Dr. Richard Cole, project director and friend who gave his guidance and encouragement as my major professor. Thanks go to Dr. Donald Hall, Dr. Charles Liston, and Dr. Eugene Roelofs for willingly serving on my committee and lending their advice and wisdom. Dr. John Gill is to be commended for his expertise and patience in dealing with statistical matters. Many thanks go to the people of the Fisheries and Wildlife department for the use of their facilities. Special thanks and credit go to Don Nelson, Mark Simons and Jim Wojcik for their assistance in the collection and processing of data as well as their comradeship during my stay here. Thanks go to Roger Jones and Julin Lu for their assistance in identification of the zooplankton samples. Above all, deepest appreciation and thanks go to my wife, Terrie, for her understanding throughout the course of this endeavor. ii TABLE OF CONTENTS LIST OF TABLES . . . . . . . . . . . . . . . . . . . . . . . . iv LIST OF FIGURES . . . . . . . . . . . . . . . . . . . . . . . . vi INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . 1 METHODS . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 The Study Site . . . . . . . Sampling . . . . . . . . . . . . . . . . . . . . . . . . . 8 RESULTS 0 O 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 1 2 Kinds of Food Consumed . . . . . . . . . . . . . . . . . . 12 Prey Selection . . . . . . . . . . . . . . . . . . . . . . 12 Age and Species of Fish and Food Selected . . . . . . . . 19 DISCUSSION . . . . . . . . . . . . . . . . . . . . . . . . . . 23 The Impact of Prey Size on Trophic Dynamics . . . . . . . L3 Conclusions . . . . . . . . . . . . . . . . . . . . . . . 47 LITERATURE CITED . . . . . . . . . . . . . . . . . . . . . . . 28 APPENDIX 0 I 0 O O O O O O O O O O O O O O O O O O O O O O I 0 3 2 iii Table A1 A2 A3 AN A5 A6 A7 A8 A9 A10 All A12 A13 LIST OF TABLES The mean sizes of available food organisms and those consumed by fish. Food electivity indices of perch, drum, white bass and goldfish. Sampling dates for zooplankton and fish. Geometric forms used to determine volume of food organisms (Weast, 1968). Differences in mean size of food in stomach contents among stations. Frequency of occurrence of yellow perch stomachs. Frequency of occurrence of bass stomachs. Frequency of occurrence of freshwater drum stomachs. Frequency of occurrence of stomachs. Percent volume of all food age class (yellow perch). Percent volume of all food class (white bass). Percent volume of all food class (freshwater drum). Percent volume of all food class (goldfish). food species in food species in white food species in food species in goldfish organisms organisms organisms organisms eaten by eaten by age eaten by age eaten by age Percent volume of foods eaten by smallest size fishes (size group 1 in Figure 5). Percent volume of foods eaten by medium size fishes (size group 2 in Figure 5). iv 16 32 33 3h 35 36 37 38 39 NO Ml h2 A3 bu LIST OF TABLES (Cont'd). Table Page Alh Percent volume of foods eaten by largest size fishes (size group 3 in Figure 5). AS AIS Mean annual electivity index for four species of fish. A6 Figure l 2 A16 A17 A18 A19 LIST OF FIGURES Map of the study area. Mean seasonal variation in the composition density of the major zooplankton groups. Mean seasonal variation in the composition of biomass of the major zooplankton groups. Percent of various foods found in stomachs of four species of fish. The relationship between the mean percent volume of a species found in the stomach and the mean volume of individual food species found in the water. The mean food size of organisms consumed by different fish age classes. Comparison of mean food sizes consumed by different species in different size groups of fish. Electivity index (Ivlev, 1960) for yellow perch. Electivity index (Ivlev, 1960) for white bass. Electivity index (Ivlev, 1960) for freshwater drum. Electivity index (Ivlev, 1960) for goldfish. vi Page 15 18 2O 22 1:7 AB 149 50 INTRODUCTION The network of trophic linkages in aquatic communities is a fundamental mechanism for population interaction. However, the quantification of trophic relations is just beginning to produce a manageable theory of trophic regulation based on a combination of results from exploratory field studies by workers like Ivlev (1961), Brooks and Dodson (1965) Hrbacek et a2. (1961), Galbraith (1966), and the environmentally simplified but highly controlled experiments of workers like Hall et al. (1970), and Werner (l97h). The purpose of this paper is to present data that will assist in the understanding of food selection processes by warm-water fishes in a highly altered aquatic environment near an operational power plant on the west shore of Lake Erie. My goal was to determine which organisms were consumed by fish and the importance of prey size in food selection. Through this process I attempted to reveal potential intraspecific or interspecific competition among fish based on food sizes alone. The mushrooming concern over man's impact on natural ecosystems hasstimulamairesearch on many ecological aspects including trophic relationships. Much of this research is designed to quantify the direction and rates of material and energy flow through natural communities. This quantification of ecological processes will allow a more accurate comparative evaluation of man—made and natural resource values resulting in more effective resource management. One outstanding example of potentially conflicting use of aquatic resources is the co—existant demand for fisheries and power plant cooling water. There is a growing realization that the effects of power plant operation on entrained aquatic organisms may be related to the size of animals which pass through the cooling system because larger animals are more vulnerable to mechanical damage (McNaught, 1972). Marcy (1973) for example has shown that nearly all of the relatively large ichthyoplankton passing through a power plant were killed. Other studies indicate that organisms of smaller size (most zooplankton) suffer less damage during passage through power plants than the larger ichthyoplankters (Davies and Jensen, 1975; Icanberry and Adams, 197A). Even though there is now no clear relationship distinctly demonstrated between size of entrained organisms and the probability of mortality, the limited existing information points to this possibility. This is especially important because prey size is one of several mechanisms by which predators choose their food (Hrbacek et aZ., 1958; Carr and Hiltunen, 1965; Galbraith, 1967; Brooks and Dodson, 1965; Hutchinson, 1971; Grygierek, Hillbricht-Ilkowska, 1966; Hall et aZ., 1970; and others). Thus, any modification of prey species composition by power plant or other similar activity may have subtle effects on fish species composition and abundance. With these concerns in mind, this study was undertaken to assess the food habits and relationships between food availability and feeding of several important fish species near a large power plant with the anticipation that future studies will define more clearly the relationships within power plant cooling systems. METHODS The Study Site This study was conducted along the western shore of Lake Erie near the Monroe power plant at the mouth of the Raisin River (Figure 1). This plant has been the focal point for a comprehensive ecological sampling program through which data for this paper were gathered. Data were taken for this study in 1971 and 1972, during which time cooling water was drawn from both the lake and river at variable rates (most frequently at about 50 m3/sec.) and discharged through a 2.5 km canal into the lake (Figure 1). At that time, the power plant was partially completed and operational shut-downs were common. Cooling processes elevated water temperatures up to 10 C as measured in the upper discharge canal. Western Lake Erie is shallow and highly turbid because of continual, wind-generated resuspension of bottom sediments and siltation from the Maumee River and other lesser tributaries. Temperatures and oxygen concentrations are generally uniform because of continuous mixing. Lake water transparency, determined by Secchi disc measurements, rarely exceeds 2 m and is most commonly less than 0.5 m. The bottom of the western basin is physically uniform and gently slopes to a maximum depth of 5 m in the study area. Geographical discontinuities along shore, like the Raisin River and the discharge canal, are the outstanding deviations from an otherwise uniform environ— ment. Figure l. Trawling Stations: I: I-5 ZOOpIankton and Benthos Stations 0 l-9 OI Monroe / Brest l’ a BI Bay I l 02 aVOQ [I I Plum // Creek N? lanst /./3 I °'°":;2:“4\' , 0’4 F52 I l P ' ’ ~ La Basance ,5 1’ Lake I . / Erie 03 I , l I L—J .6 lkilometcr Map of the Study Area Perhaps because of physical uniformity in this system, zoOplankton populations are also relatively uniformly distributed throughout the study area. Nalepa (1972) has shown that the "relative densities and biomass (expressed as %) of the major zooplankton taxa varied little within the lake" (Figures 2 and 3). Greatest variance from mean composition throughout the study area occurred in the river and inshore discharge area. Although on a given date, variations among stations within the study area are up to 100% or more, they tend not to be consistant in the lake from one sampling date to the next; therefore, variations are dampened over an annual cycle. To check Nalepa's findings, additional triplicate zooplankton samples from the fish and zooplankton collecting sites were collected and compared for two separate dates. A multivariate ANOVA likelihood ratio test (Kramer, 1972; Harris, 1975) was run and no significant differences were indicated between collection stations. Nalepa (1972) also found that vertical planktonic variation was less than the horizontal variation observed over the study area, usually with less than a 20 to 30% difference. The homogeneous character of western Lake Erie was remarked upon by Verduin (196A) and the IJC (1969), and if the food in the study area is homogeneously distributed, then the potential for differential prey concentrations influencing food composition in fish stomachs is negligible. Therefore, selection indices which are calculated from samples obtained over a seasonal time span and from widely divergent regions of the study area should minimize the probability of identifying a size selection process if it occurs because of the array of temporal and spatial variability incorporated .Amema .wmmaaz Soamv .mcmsmoo©SHOIwaHQfipm anpcn amcchQcleesm smmfic mflcpwe "mammfiposnmaumflpm gob .mmscsw copxcmaaoou homes map go hpwmcmc HeQprmucQfico map pa :oflpmflsmb Hmccmmmm semi .m madman .Amema .mamaaz Eosmv .mcwseoopwfionosflamflpm Ecppop "mpommmooummsm ammao mavews mmsmwflposlmcfifimwpm moB .mQSosw copxcmamoow Lemma map mo mmwsoflp so eoflpwmomsco map as cofipmwam> accommmm new: .m mssmflm in the analysis. Any selection that can be identified under these variable conditions should point to the generality of any selection process shown and increase our confidence in its validity. In view of these considerations my work is not like the classical electivity studies which dictate simultaneous sampling of predator and prey at the same location (Ivlev, 1960). That type of study has been criticized by O'Brien and Vinyard (197A). It is rarely known whether or not the predator and the prey are collected from the same place where feeding interactions occurred because fish are mobile (Sigler, 19h9; Hasler et aZ., 1969), plankton are carried by currents, and there are often delays of hours or more in the digestion of fish stomach contents (Pearse and Achtenberg, 1920; Seaburg and Moyle, 196A; Noble, 1973). Sampling The sampling sites were located in the most disparate environments found in the study area: from the mouth of the Raisin River, the discharge canal and the lake. These were the same sites sampled by Nalepa (1972). This scheme ensured that any spatial heterogeneity in prey distributions which could confound our results would be identified. Fish and zooplankton samples were collected from the study area usually within 2h hours of one another at five sampling sites (see Appendix, Table A1). At the three lake stations fish were collected within one km of the zooplankton sampling station. Benthic samples were obtained from the same locations where zooplankton were collected and within a week of fish sampling. Fish, zooplankton, and benthos were sampled at the same Site in the river and discharge canal. It is very difficult to sample the water-sediment interface effectively and dense concentrations of various plankters may have occurred there and biased the results. However, Nalepa (1972) indicated that day and night samples were not consistently greater or different in con— centrations of important zooplankton species. Therefore, daily migration which could cause high concentrations near the bottom at certain times of the day do not seem to have much impact in the study area. Triplicate zooplankton samples were taken with an 8 liter VanDorn water bottle from 2.5 m (about mid-depth), filtered from h liters with a #25 Wisconsin plankton bucket and washed into a vial with 5% formalin for preservation. Animals were identified to the lowest possible taxa and counted using a Sedgwick—Rafter cell and a binocular scope at 100x. Lengths and widths of each individual were measured and an estimated third dimension was calculated as a proportion of the length from ratios derived from actual measurements. The volumes of the animals were then calculated by assuming the shape of each species was represented by an appropriate simple geometric form or combination of such forms (see Appendix, Table A2). Benthic animals were treated in a similar manner. Four fish species were included in this study because of their importance based on abundance and economic value. The species examined were: goldfish, Carassius auratus (Linneaus); white bass, Mbrone chrysops (Rafinesque); freshwater drum, ApZodinotus grunniens (Rafinesque); and, yellow perch, Perca flavescens (Mitchill). The fish were collected with a 5 m otter trawl in duplicate five minute tows over an area of approximately 0.5 h. Fish were preserved in formalin 10 and aged from scales and length—frequency data. Later, the gut contents including the entire alimentary tract were analyzed by removing the stomach contents from the gut. Food organisms were suspended for subsampling and examination in a Sedgwick-Hafter cell under 100x. The volumes of these animals were calculated similarly to the volumes of those captured in water samples. When only parts of prey were found in the stomach, the volume of the whole animal was calculated from appropriate proportions. At least 20 organisms were counted from each stomach used in the analysis and each was identified to the most specific taxon possible. Food sizes in different age classes of each fish species were contrasted among and within species using ANOVA tests after the data were corrected to homogeneous variances by log transformation (Sokal and Rohlf, 1969). Tukey's multiple range comparisons were used to sort mean values at a = 0.05 when differences were determined to be significant (« = 0.05) in the ANOVA (Glass and Stanley, 1970). All comparisons were made without reference to specific dates or stations sampled. This is acceptable because no seasonal trends in sizes of prey consumed were suggested by plotting size of food against the time of the year and no identifiable differences in mean size of organisms in the stomach contents existed among stations (see Appendix, Table A3). Electivity indices (Ivlev, 1960) although mostly qualitative, were calculated to identify possible selection of specific zooplankton taxa over the study period. A multivariate T-test (Gill and Hafs, 1971; Kramer, 1972) was employed to test the hypothesis that fish select certain zooplankter foods from their environment rather than consume ll them in proportion to their abundance. The regression of prey size distribution and size of food organism in stomachs was also analyzed to assess the effect of size on the selection of prey. RESULTS Kinds g£_Food Consumed The stomachs of the four fish species included in this study contained a wide variety of organisms, but size of prey appeared to be a primary cue used to select foods (Table 1; Figure A). Some very rare but large organisms were found in the stomachs but not in the aquatic environment. Of the large organisms found in the water and benthic zones, only oligochaetes were absent in the stomachs (Table 1). Most frequently the favored foods included midge (Chironomidae) larvae or the large cladoceran, Leptodbra kindtii (see Appendix, Tables Ah-A7). The size of these two food types far exceeds that of other foods found in these fish (Table l). Goldfish stand out as the exceptional species which contained foods of intermediate rather than larger sizes, especially the cyclopoid copepods. Prey Selection Stomach contents and species lists for the aquatic environment alone can do little more than suggest the potential importance of food selection from the potentially available prey species. Electivity indices for zooplankters demonstrate the regularity of selection of larger zooplankters and results of the multivariate T—test indicate the statistically significant (a = 0.05) selection or rejection of prey species (Table 2; Appendix A15-Al9). All four species showed 12 13 XXX 'x ><><>< ><><><>< >< ><><><>< ><><><>< m.mwna.m ease mzo mmtm momum mmmmuemm ooo.eomuoemm ooo.somuomme r-ICUMJ m.ma m.:m mama owmwm mmhmm .am mssopmxb .am sawEmom +wsmxooasmcoa mzmsoooaarob +mofiooflpomgawm exawmcaa maoNomooaoss mauepwamsome maoNomo mchasma onNomb mpomoaoho mwakac eaosmumssm memamsomoso mzsouaoeq mopwonowm mzsoaaewm merowm mssouaewq negates mascaaewm «prcName mzsouaewm wewoewawo .am swcaacpowaob seawmamcsouxome csomorcxmusa Sassoosums ewaxacm measures casmNcm owzaaem Eases 23833 .mm waspsNoosm .am wxsososwab Smwwoaou mmmm means Essa smpmz Tammam nosom soaaes nocsopm nmwm cw Axv mocmmoam x 1 @0H m mmcwm m magmas Mom oaflm mocmsommm m sax: m .mnHm coo: seen: one ca venom memficwmao poem .nmwm an oosdmcoo moose use mEmwcmmso ooow manmawm>m no woman came one .H oHQmB 1h .msemsopm m so H afico ea coco possSOOo Emflcmmso Loom .x. .mcmeflomam Sea hso> .m>flpmpcommamma pom hanmposm+ x *neaeeem ewes x mm *AOpflS soemkv wwsaoo< x oem.om *mneaaaseooeesm x 00:.mw *omofiaoammoseam x owm.mea *eeoaaeaee x Ome.mqa smoomomH x x x meuom m.me nameaeam seeeaeo x x x omI: o.aa .am mxuamsoomma x x x HmIe m.wa .an eeeNe mme<2 zH eoz eam .mmoqsoem 2H canoe goes cem.mmuomw moem newneomaao x x x m.aauwo. a me. enemapom m.HImH. I w. wflamsmc pomeoo enseeaoo ennm seem enema OH x a m enemas OH x a swan; map as Opesz amps: soaaow m owcmm sow mafim moaam m endow memflcmmso pooh lawman mocmsommm can: coosopm swam ca Axv mocmmosm Ae.peoov a manna 96 volume in stomach Figure A. Percent of various foods found in stomach of four species of fish. 16 Table 2. Food electivity indices of yellow perch, freshwater drum, white bass and goldfish.l Fish Species Studied Food Species Yellow Freshwater White Consumed Perch Drum Bass Goldfish Leptodora +0.71* +0.62* +0.6h* +0.38 Daphnia —0.13 -0.63* -0.82* -0.89* Calanoida +0.12 -0.98* -0.98* -0.79* Cyclopoida +0.26 +0.06 -O.32* +0.61* Bosmina -0.h2* -0.96* -0.73* -0.32* Chydorus -0.07 -O.89* -O.66* —0.07 Rotifera -O.99* -l.0 * ~0.98* ~0.99* lAll fish greater than 50 mm. Denotes significantly different from zero at s 0.05 determined a multivariate T, Student's t and approximate t tests. 17 some selection based on size but size-independent factors probably are responsible for selection among similarly sized smaller organisms. Among the four species, goldfish was the exception which selected for cyclopoids rather than L. kindtii as its main food item. Although prey size seems to be an important selection factor for at least 3 of the A species examined, not one of the coefficients for regression analyses of the zooplankter stomach contents of the size composition of available zooplankton foods was significant (Figure 5). Addition of benthic forms reduced the regression coefficient for all species except drum, which increased somewhat but remained non—significant. Compared regression coefficients for data with and without benthic foods were significantly different for white bass, and drum (p g_0.0h that r values are the same), while coefficients were similar in perch and goldfish (p > 0.12 and 0.35 respectively that r values are the same). Although none of the relationships shoWn in Figure 5 were statistically significantly different from zero at a = 0.05, both bass (r = 0.666) and drum (r = 0.705) would be different from O at a = 0.10 while perch (r = O.hhh) and goldfish (r = 0.279) would be different only at much higher probabilities. Data shown in Figure 5 were logarithmicaly transformed because the actual values essentially resulted in a regression line between two widely divergent clumped groups of large and small organisms. The size selection of the benthic animals from bottom sediments may be obscured because position of the food in the sediment profile has such a marked impact on availability to the predator. Percent volume in stomach Figure 5. 1e '00,Y. PERCH Daphniao kepi‘g‘m'“ I0 - 6 Cyclopoid. ChIrOflOfl'tU.3 8 Chydows'oeosmina 7 Lo . Calanoid' 5 2 ProclodiDs .l - 9 ORotifera .Ol - .00| - r with benthos = .444 r without benthos = .5|8 .000! . . 1 ‘ 4 IOO _ GOLDFISH 6Cyplopoid 8 'Ch dorus '0' Bosminao7 . y ChIronomusu Lept dam-3 . - ' 4 . '0 DaphnI. ProcladIIIsz Colanoid 5 .l - r with benthos=.279 r without benthos=.3l2 9 Rotlfera . | 1 L L 1 ° 5 - e 8 °- 9 l00,000 I- . F. DRUM Chironomusol o 3 Leptodora T P Icii'2 Cyclopoidoe roca us 4 o Daphnia 8 ’ Chydorus - 7 ‘ Bosmina scalpnold r with benthos = .705 I; without benlthos =..644 _ . .BA L§§ Leptodora.3 Chironomus “ Cyclopoid " ProcladiTISZ 8 Chydorus: . Daphnia 4 7 Bosmina 9 'Rotifero 5 .Colonoid r with benthos= .650 r wIthout benthos=.698 I CD .00l - I000 - I00,000 I- Meon volume (p.3x l0°)of individual food item M The relationship between the mean percent volume of a species found in the stomach and the mean volume of individual food species found in the water. Numbers denote size relationships among species. (Table I) Percent volume in stomach IOOrY- PERCH Daphnia. kepi‘gdm“ l0 - 6 CyCIOpoid. Chironomup 8 Chydo'US'OBosmina 7 LC . Calanoid‘ 5 2 Procladias .l - 9 0Rotifera .0I - '- r with benthos = .444 r without benthos = .5l8 .000. n L 1 I __n l P GOLDFISH 00 6 Cyglopoid 8 ' Ch dorus '0 - Bosminao7 . y ChIronomuSoI Lept doraos , ' 4’ . I OI. DaphnI Procladu‘tsz Figure 5. .00I .Ol 16 Calanoid’s . - r with benthos=.279 r without benthos=.3l2 9 Rotifera L 1 -. O .OOI - I000 ~ IOO,OOO I .. F. DRUM Chironomuso I o 3 Leptodora r .o 2 CYCIOpOid.6 Procladuus 4 o Daphnia 3 ‘ Chydorus - 7 ’ Bosmina SColpnold r with benthos = .705 1 without ben‘thos =..644 _ .. . A w—B—fi—S' Leptodora.3 Chironomus. I CYCIODOId. ProclodiTIs2 BChydorus: ODaphnia 4 7 Bosmina 9 'Rotifera 5 .Colanoid r with benthos= .650 r without benthos =..698 L 1 1 ‘1 C) .00l » IOOO I00,000 b Mean volume (p3xl05)of individual food item M The relationship between the mean percent volume of a species found in the stomach and the mean volume of individual food species found in the water. Numbers denote size relationships among species. (Table I) 19 Only among drum is the largest available food organism, Chironomus sp., the most commonly consumed, with L. kindtii a close second. In white bass and yellow perch, L. kindtii was most commonly consumed rather than the larger benthic animals which were perhaps capable of avoiding capture by less effective benthic feeders through burrowing out of sight in the sediments. The benthic midge Procladius sp., in no case was preferred to Chironomus sp.cn~L. kindtii even though its size was very similar to Chironomus Sp. Procladius sp. is translucent and Chironomus sp. is red and more likely to be visible in the sediments. In goldfish the preferred species were intermediate in size. The smallest foods, rotifers, contributed least to food volume in yellow perch and goldfish. These organisms are so small that it is possible they were consumed accidently in association with other food. In that case, Basmina longirostris and Chydorus sphaericus would have been the smallest of the "selected" foods. Calanoid copepods may have avoided selection by all fish (Lindstrom, 1955) as they avoided tow nets (Fleminger, 1965) while cyclopoid copepods were more susceptible to predation. Daphnia sp., relatively large cladocerans, were negatively selected, possibly because of their transparency. Age and Species 9£_Fish and Food Selected If fish food selection is determined substantially by size, the potential exists in the study area for both intraspecific and inter— specific competition because the sizes of food used by most of the fish species examined differed little after they reached a certain age (Figure 6). At present, zooplankton food does not appear to be in short supply in the very productive western basin. The mean size 21 of all food consumed by an individual species differed (a = 0.05) among age classes only in the young-of-the—year freshwater drum. Yellow perch also exhibited a trend in the relation between age and food size and when the more size-variable benthic organisms were deleted from the analysis, the young-of-the—year perch exhibited stomach contents with sizes that differed from ages 2 through A. For the most part, the mean size of food in stomach contents varies little once the fish in all four of these species reach 6 to 10 cm (see Appendix Tables A8-All). Based on food size alone, there seems to be enough difference (a = 0.05) in the stomach contents of young—of—the-year fish to preclude intensive interspecific competition at this size (Figure 7). But, as the fish grow larger, differences in food sizes among three of the four species are not apparent. This is at least partly caused by greater variation in the food sizes eaten by larger fish. Goldfish again stand apart as the least likely to compete with any of the other species examined as the mean size of prey in their stomach contents is significantly less than that of the other species (see Appendix Tables Al2-Alh). 20 E Mean with standard error 95% Confidence interval includes no Benthoc 95% Confidence interval for data includes Bonthoc E 30 I I T a: 325» I I I g 4: ' I E! E ’2 .\‘Z I % ' E : 2°“ a. ; 0 I5- ' l . '5 I 5 I g g 3 we : : . 3 E .3 ' 5" ' | ' ' I I I 5 I I-Iz {"4 3 ' L r7 II V I r: E . ii A . E 4 v . Q'IO g I E I '5 \L9 N —' v . El E | O l I L - I a! ' '5 '8 ' a) 3 I ' L _ LEI e ' . ~ 7 MI 5 ' \ \ 3 5 '4 I-c \ \' 3 Z : I A LInc? O - t- 8 2 '3: :15 E: ' k \r | s ' I. :3 r2 If I I 'o , .. ' “5’ I" . I ~ r We 5 | I I rl I ACE oIII oIII2-7IIO ]I|2[3|olfl2|3 45 BASSIPERCHI DRUM ] GOLDFISH Figure 6. The mean food size of organisms consumed by different fish age classes. Note that each fish species is on a different scale and that these are different than those shown on Figure 7. 22 E = NIEAN wmI STANDARD ERROR = 95% CONFIDENCE iNTERVAL SIZE I SIZE 2 SIZE 3 AGE 0 AGE I-m AGE III-Y I I 25 'g I I. as 3 a» I BEIE I I g3 I 5 w- I I z E' I [LI § 5~‘ ' I I“: o I I I . V - I . ; I - I . L ME 5.. I ' E I I g 4' I§§ I In I 2 '3' ' § In 3" I ll ' S t . § : o il§ . O 2* | > I 0 § u. I '\ ' I Ii . I' I I \ I I I S E I I m I :m I x z: 5w§2 owge 0 =9 «41¢ ¢<¢u 5 mm mono “man a on a l 4 a 8 o (.9 ‘9 c Figure 7. Comparison of mean food sizes consumed by different species within different size groups of fish. Fish of different species were selected for similar size without specific reference to age. Therefore age and size catagories only approximate each other. DISCUSSION The Impact g£_Prey Size 9E_Trophic Dynamics Size selection of prey by fish predators has been discussed at length by many workers (Carr and Hiltunen, 1965; Galbraith, 196T; Reif and Tappa, 1966; Hrbacek, 1958; Wells, 1970; Brooks and Dodson, 1965; Brooks, 1968; Hutchinson, 1971; and others). Size appears to play a role in the food selection process of fish in western Lake Erie, particularly in the zooplankter component. But, because so much of the size related choice depends on one or two prey species in Lake Erie (Leptodora kindtii and Chironomus Sp.) there remains some doubt that prey size is the primary selective cue used by the predator. Size could be only spuriously related to some size independent vulnerability, such as speed of movement, opacity or contrast. The fact that large benthic organisms were actively selected by two of four fish species even though the zoobenthos are physically more likely to be obscured than zooplankton strengthens the belief that size is an important regulatory factor. The smaller zooplankters appear to be selected on the basis of characters other than the relatively minor size differences that exist among them. Relative density of prey probably becomes more important, but certain prey groups seem to be vulnerable to predators ifor reasons other than size or density. Other workers have described IDhenomena which may influence the visual selection of organisms for food. 23 2h Zarret (1972) thought that large eye spots and dark digestive tracts in prey'lnay trigger selection; and brightness, contrast (Hemmings, 1966) and color (Ginetz and Larke, 1972) may also be involved. Greze (1963) hypothesized that transparency as a form of protective coloration was important; the more opaque the organism, the greater is its susceptibility to predation. The actual sighting range of a predator probably depends on prey size, contrast, and illumination. In Lake Erie, the latter is markedly influenced by excessive turbidity. Brooks (1968) felt that movements would attract fishes to an organism and Hall et a2. (1970) thought that in addition to body size, selection also involved the habitat, abundance, and the vulnerability, competition and activity of the prey species. Some species of zooplankton are capable of avoidance reactions; notably the calanoid copepods and L. kindtii (Szlauer, 1967; Szlauer, 1965; Lindstrom, 1955; Aron and Collard, 1969). It appears from these investigations, as well as others, that prey size selection operates most effectively when a wide choice of sizes is available. As the range of different prey sizes diminishes, other selection cues must be utilized. Brooks and Dodson (1965), Galbraith (1967), Hrbacek et a1. (1961), and others believed that fish selected the larger, competitively superior feeders which allowed a greater diversity and abundance of smaller species to develop. The hypothesis that a minimum size threshold exists for prey before perch, bass and drum actively seek those organisms is supported by LeBrasseur (1969), Brooks (1968) and others who found that organisms below a given size range were ignored or rejected when larger alternative organisms were present. According to Hall et al. (1970) fish consume a greater diversity of species when food is scarce although generally they eat the largest food possible. 25 Each of the four species of fish investigated in the study consumed unique combinations of prey species but virtually all species were consumed by each fish species. Therefore, it is possible that a loss of any one relatively important prey species could cause a shift in feeding intensity on the remaining prey organisms and in turn affect the relative growth and distribution of the fish species. Any new size related shift in prey abundance, such as might be caused by power plant operation would be less likely to directly influence fish like goldfish than species like white bass, drum and perch which depend heavily on large food organisms. A shift of this type may have already occurred following the depressed oxygen levels of the mid—1950's. Historically, these three fish extensively used even larger benthic food items (Price, 1963) such as large burrowing mayflies (Hexagenia), caddisflies (Trichoptera), scuds (Amphipoda), sowbugs (Isopoda), and fingernail clams (Sphaeridae), but these populations have been decimated since the early 1950's when mortalities associateu with extreme oxygen depletion was first recognized in the western basin of Lake Erie (Britt, 1955; Verduin, 196h). Extremely low oxyaen levels have occurred repeatedly in the western basin since then and apparently contributed to the demise of intolerant species and the depression of food size diversity. Carr and Hiltunen (1965) reported that from 1930 to 1960 Hexagenia had dropped to 1% of its former abundance, while tubificids had increased ninefold and chironomid larvae had increased fourfold. Tubificids apparently are not available as food to most fish even though they are relatively large probably because they move quickly into the sediments. With Hexagenia and 26 other large benthic species decimated, the fish were forced to rely more on chironomid larvae and zooplankton. Although the total biomass of benthic organisms present may have remained the same or even increased over time in Lake Erie, the number of large species available for consumption has been drastically reduced. At the present time, zooplankton prey density does not appear to limit growth, but their small size, in relation to predator size, may have decreased fish feeding efficiency and depressed fish growth rates. Power plant entrainment may cause more damage to larger plankton like L. kindtii than to smaller species of zooplankton because they could be more susceptible to mechanical damage in once—through cooling systems (McNaught, 1972). Normally, sustained growth rates require increasingly larger prey as the predator becomes larger. LeBrasseur (1969) and Kerr (1971) discuss the importance of efficient feeding based on the relative energy costs required to capture a few large organisms compared to many small ones. Growth efficiency probably decreases when these prey organisms become rare or small in relation to the predator size because the metabolic cost of excessive searching for food is appreciably higher, according to Pierce and Wissing (197M) than normal swimming activity alone. In Lake Erie a restricted few, relatively small prey species are consumed by all fish older than a few months, and although they appear to be fairly abundant, this may contribute to depressed growth rates in older fish. Any additional negative impact on larger food organisms could depress growth rates further in all age groups of size—selective feeders and favor growth in fish species that are less likely to select food by size. Because of these potential effects, power plant cooling operations could cause 27 indirect and subtle, but real changes in the fisheries resource. These speculations deserve attention in further refined studies of power plant effects on entrained organisms. Conclusions 1. Large prey organisms (specifically Leptodora kindtii and Chironomus sp.) are selected for food by freshwater drum, white bass and perch. Goldfish select smaller prey species; particularly cyclopoid copepods. 2. Among freshwater drum, white bass and perch, fish older than age 1 eat similarly sized organisms and therefore may compete inter- specifically. Young-of—the-year fish are less likely to compete because the food sizes consumed are more diverse. Goldfish eat different sized foods from the other fish species at all ages, so are unlikely to compete interspecifically. 3. All ages but young-of-the—year fish in each species eat food of about the same size and may compete intraspecifically. h. Given a history of decreasing size diversity in fish food organisms in western Lake Erie, any further depression, such as might possibly result from an increase in the number of power plants and other operations, could cause subtle changes in fish species composition and growth rates which may favor fish species like goldfish and disfavor fish species like perch, drum and white bass. Additional data on power plant effects on the prey are needed to validate these speculations. Extensive quantitative data describing the extent of impact on prey populations and differential, size related mortality are needed to make management recommendations. LITERATURE CITED LITERATURE CITED Aron, W. and S. Collard. 1969. A study of the influence of net speed on catch. Limnol. and Oceanogr. 1h(2): h2h—h29. Britt, N. W. 1955. Stratification in Western Lake Erie in summer of 1953, effects on the Hexagenia (Ephemeroptera) population. Ecol. 36: 239-2hh. Brooks, J. L. and S. I. Dodson. 1965. Predation, body size and composition of plankton. Science 150: 28-35. Brooks, J. L. 1968. The effect of prey size selection by lake planktivores. Syst. 2001. 17: 273-291. Carr, J. F. and J. K. Hiltunen. 1965. Changes in the bottom fauna of western Lake Erie from 1930 to 1961. Limnol. and Oceanogr. 10: 551—569. Davies, R. M. and L. D. Jensen. 1975. Zooplankton entrainment at three mid-Atlantic power plants. J. Water Poll. Cont. Fed. h7(8): 2130—2192. Fleminger, A. and R. I. Clutter. 1965. Avoidance of towed nets by zooplankton. Limnol. and Oceanogr. 10: 96-10h. Galbraith, M. G., Jr. 1967. Size-selection predation on Daphnia by rainbow trout and yellow perch. Trans. Am. Fish. Soc. 96(1): 1-10. Gill, J. L. and H. D. Hafs. 1971. Analysis of repeated measurements of animals. J. Animal Sci. 33(2): 331-336. Ginetz, R. M. and A. Larke. 1973. Choice of colors of food items by rainbow trout (Shlmo gairdneri). J. Fish. Res. Ed. Can. 30(2): 229—23h. Glass, G. V. and J. C. Stanley. 1970. Statistical Methods ig_§ducation and Psychology. Prentice—Hall Englewood Cliffs, New Jersey. 596 pp. Greze, V. N. 1963. The determination of transparency among planktonic organisms and its protective significance. Dolk.-Biol. Sci. sec. (Eng. Trans.), 151(2): 956—958. 28 29 Grygierek, E., A. Hillbricht-Ilkowska and I. Spodniewska. 1966. The effect of fish on plankton community in ponds. Verh. Int. Ver. Limnol. 16: 1359-1366. Hall, D. J., W. E. Cooper and E. E. Werner. 1970. An experimental approach to production dynamics and structure of freshwater animal communities. Limnol. and Oceanogr. 15: 839—928. Harris, R. J. 1975. A primer of multivariate statistics. Academic Press, New York, N. Y. 332 pp. Hasler, A. D., E. S. Gardilla, R. M. Herrall and H. F. Henderson. 1969. Open water orientation of white bass, Roccus chrysops, as determined by ultrasonic tracking methods. J. Fish. Res. Ed. Can. 26: 2173-2192. Hemmings, C. C. 1966. Factors influencing visability of objects under- water. p. 359-37h. in R. Bainbridge, C. C. Evans and 0. Rackham, Light as an Ecological Factor. John Wiley and Sons, Inc., New York, N. Y. Hrbacek, J., M. Dvorakova, V. Korinek and L. Prochazkova. 1961. Demonstration of the effect of fish stock on the species composi- tion of zooplankton and the intensity of metabolism of the whole plankton association. Verh. Int. Ver. Limnol. 1h: 192-195. Hrbacek, J. M. 1958. Density of the fish populations as a factor influencing the distribution and speciation in the genus Daphnia. Proc. Int. Cong. Zool. 15: 79h-796. Hutchinson, B. P. 1971. The effects of fish predation on the zoo- plankton of ten Adirondak lakes with particular reference to alewife, Alosa pseudoharengus. Trans. Am. Fish. Soc. 2: 325— 335. Icanberry, J. W. and J. R. Adams. 197A. Zooplankton survival in cooling water systems of four thermal power plants on the California coast. Proc. 2nd Workshop Entrainment and Intake Screening, Cooling and Water Discharge, Project Rept. 15. Electric Power Res. Inst. Publ. No. 7h-0h9100-5. International Joint Commission. 1969. Report of the International Joint Commission, United States and Canada on the pollution of Lake Erie, Lake Ontario and the international section of the St. Lawrence River. Vol. 2, Lake Erie, 316 pp. Ivlev, V. S. 1960. On the utilization of food by planktophage fishes. Bull. Math. Bio. 22: 371-389. Ivlev, V. S. 1961. Experimental ecology gf_the feeding of fishes. Yale Univ. Press, New Haven, Conn. 302 pp. Kerr, S. R. 1971. Prediction of fish growth efficiency in nature. J. Fish. Res. Ed. Can. 28(6): 809-81u. 30 Kramer, C. Y. 1972. A first course in methods of multivariate analysis. Virginia Polytechnic Inst. and State Univ., Blacksburg, Va., published privately by author. 320 pp. LeBrasseur, R. J. 1969. Growth of juvenile chum salmon, Oncorhynchus kita under different feeding regimes. J. Fish. Res. Ed. Can. 26(6): 1631-16h5. Lindstrom, T. 1955. On the relation fish size—food size. Report Institute of Freshwater Res. Drottingholm 36: 133—1h7. Marcy, 3. C. 1973. Vulnerability and survival of young Connecticut River fish entrained at a nuclear power plant. J. Fish. Res. Ed. Can. 30: 1195-1203. McNaught, D. C. 1972. The potential effects of condenser passage on the entrained zooplankton at Zion Station. in Review of Recent Technical Information Concerning the Adverse Effects of Once- through Cooling on Lake Michigan. Prepared for the Lake Michigan Enforcement Conference, Sept. 19—21, 1972, Chicago, 111. By Thomas A. Edsall and Thomas G. Yocom. Meglitsch, P. A. 1972. Invertebrate Zoology. Oxford Univ. Press, New York. 83h pp. Nalepa, T. F. 1972. An ecological evaluation of a thermal discharge, Part III: The distribution of zooplankton along the western shore of Lake Erie. M.S. Thesis, Mich. State Univ., Tech. Rept. #15, Inst. Water Research. 112 pp. Noble, R. L. 1972. A method of direct estimation of total food consumption with application to young yellow perch. Prog. Fish Cult. 3h(h): 191-19u. O'Brien, J. W. and G. L. Vinyard. 197M. Comment on the use of Ivlev's electivity index with planktivorous fish. J. Fish. Res. Ed. Can. 31: 1927-1h29. Pearse, A. S. and H. Achtenberg. 1920. Habits of the yellow perch in Wisconsin lakes. U. S. Fish Bull. 36: 293-366. Pennak, R. W. 1953. Freshwater Invertebrates gf_the United States. Ronald Press Company, New York. 769 pp. Pierce, R. J. and T. E. Wissing. 197M. Energy costs of food utiliza- tion in the bluegill, Lepomis macrochizus. Trans. Am. Fish. Soc. 103(1): 38—h5. Price, J. W. 1963. A study of the food habits of some Lake Erie fish. Bull. Ohio Biol. Surv., Vol. 2: 1-89. Reif, C. B. and D. W. Tappa. 1966. Selective predation: smelt and cladocerans in Harveys Lake. Limnol. and Oceanogr. 11(3): h37—h38. 31 Seaburg, K. G. and J. B. Moyle. 196M. Feeding habits, digestive rates and growth of some Minnesota warmwater fishes. Trans. Am. Fish. Soc. 93(3): 269-285. Sigler, W. F. l9h9. Life history of the white bass in Storm Lake, Iowa. Iowa State J. Sci. 23(h): 311-316. Sokal, R. R. and F. J. Rohlf. 1969. Biometry. W. H. Freeman and Co., San Francisco, California. 776 pp. Szlauer, L. 1965. The refuge ability of plankton animals before models of plankton eating animals. Pol. Arch. Hydrobiol. 13: 89-95. Szlauer, L. 1967. Investigations upon ability in plankton crustacea to escape the net. Pol. Arch. Hydrobiol. 15: 79-86. Usinger, R. L. 1971. Aquatic Insects gf_California. Univ. of Calif. Press, Berkley, Calif. 508 pp. Verduin, J. 196M. Changes in western Lake Erie during the period 19h8—1962. Verh. Int. Verein. Limnol. 15: 639—6hh. Ward, H. B. and G. C. Whipple. 1963. Freshwater Biology. 2nd ed. Wiley and Sons, Inc., New York. 12A8 pp. Weast, R. C. ed. 1968. Handbook of chemistry and physics. h9th ed. Chemical Rubber 00., Cleveland, Ohio. 2300 pp. Werner, E. E. 197D. Fish size, prey size, handling time relations in several sunfishes and some implications. J. Fish. Res. Ed. Can. 31(9): 1531—1536. Wells, L. 1970. Effects of alewife predation on zooplankton popula- tion in Lake Mendota. Limnol. and Oceanogr. 15: 556—565. Zaret, T. M. 1972. Predators, invieable prey and the nature of poly- .morphism in the cladacera (class crustacea). Limnol. and Oceanogr. 17(2): 171—183. APPENDIX 32 Table A1. Sampling dates for zooplankton and fish. Zooplankton Fish Collection Collection Dates Dates 05/11/72 05/11/72 05/31/72 06/02/72 06/13/72 06/1h/72 06/27/72 06/29/72 07/11/72 07/12/72 07/25/72 07/25/72 08/16/72 08/16/72 08/29/72 08/29/72 09/12/72 09/13/72 09/29/72 09/30/72 10/13/72 10/13/72 10/27/72 10/27/72 07/1h/71 OT/lh/Yi 07/30/71 07/29/71 09/02/71 08/31/71 09/17/71 09/16/71 10/02/71 09/31/71 10/15/71 10/15/71 10/31/72 10/30/71 12/07/71 12/07/72 33 Table A2. Geometric forms used to determine (Weast, 1968). volume of food organisms Daphnia sp. 1/6 n abc Alana sp. where a = length - measured excluding tail spine b = width — measured at widest point c = depth - (.29)a Daphnia ephippia Uiaphanosoma sp. . 3 Chydorus sp. h/j n r where r = 1/2 the length or width Bosmina sp. 1/6 w abc [Zyocryptus sp. where a = length - measured at widest point b = width - measured at widest point c = depth - (.Sl)a Cyclop01da fire a + nr2a Calanoida where r = 1/2 width at widest 2 point a = length excluding caudal setae Harpacticoida O Chironomid larvae nr”a where r = 1/2 width at widest point a = length excluding caudal setae Leptodora kindtii nr2a where r = 1/2 width of the main body segment at widest point a = length of the tail x a factor based on the width of the tail at the very base, which was based on proportional measurement of the whole of the body parts woooo. om mmoo. Moshe sense OH. $0.: n Aem.ev mc.o u e Hmooo. a mooo. mess mmo. m mm.m n (flees soooo. em mmoo. Hesse was. H smeeefiom eases emo.m em mma.mma sosse mm®.m m Om. mm m n Amm mv mo WHMQQ moo.m m 000.0 mpsp moo.m m Edam cam. u a sem.s mm sma.mmfl Aesop mmfi.m H seeessmmss mmm.m s mHLsp sos.m am mmN.Hm sopsm eme.m m . .m. H Jn . H on so c Ase mv mo mason ems.s m mm:.ma mess wmm.m m sam.a n e smm.m em omm.mm fleece msa.m a mmsm sees: muses 0mm.s mm mom.mfifi sesse see. m ma m u Amp av mo WHMoo sea. m 4mm. mpnp .mme. m me.A see. u e mesa mm mmm.mHH asses msw. a sesmm sesame mpflHmeQOLQ oHpmp :w: mstdm .w.p mmsmsdm mo ESm mcwmz hmnfidz mmflomgm nmwm cmmz sofipwpm .mGOfipwpm macaw mpcmpsoo nomSOPm ca doom mo Amaavomfim Gems ofl moosommweflm nm< mHQwB 35 mm.s mm 1. w u- s m ssmsepom mw.:a Om m: ma om : ma mssopmab mw.mm om II Hm om NH mm dawsmom mm.bm m» II w om Hm om mofiomofiozo mm. In :1 w I: nu In manmmhoomNH mm.:H I: I: :1 om : mm wwwocdawo ms.mm In em an 0: mm mm essence mm.mm mm a» m: om mm mm esopoummq mm. In In In In a II owpfinohmmoaphm mm. In 1: In In I: m mammssuomNmoo em.m I: II II In a m opopwsoz mm.e m I: I: OH m m mswpsNoogm m©.:m om mm mm om mm o: mgiogwfi mm.s mm .1 7. OH 7. s assesses mmm< Has > was >H was HHH mw< HH mm< H mw< o ems mmeemmm woos : h ma OH :N m: nmflm mo .02 .wmnSUUO mwfiommm doom Sufigs cfi mnemSOpm nonmm zoaamm mo pcooaom .s¢ mapme Table A5- Percent of white bass in which food occurred. 36 No. of Fish 25 16 Food Species Age 0 Age I All Ages Chironomus hO -- 2h.39 Procladius 32 -- 19.51 Nematoda 16 13 lh.6 Leptodora 100 75 90.2h Daphnia ephippia l2 -— 7.32 Daphnia 56 25 h3.9 Ceriodaphnia 8 -- h.88 Alana h -— 2.hh Calanoida 12 25 9.76 IZyocryptus h -- 2.hh Cyclopoida 6O 56 56.] Bosmina AC 38 39.02 Chydorus 2h 12 19.51 Rotifera -— 6 2.hh Fish Bones 8 31 17.07 Fish Scales MA 50 06.3h Tape Worm l6 hh 26.83 (Y‘: 37 Ln (0 01 LC m \0 (_\J CO U‘\ .1! 1 UR. (u (I; mocom cmflm mmesem sees meiomomxb cswsmom deflomcHomo assassoome mpfiocwawo dsomfl UEomo:6&onQ swsausm wflamwzmo Gwsxmsm osoponmmm mpopmsmm wstQwoosm msEoroswxb (1) hi. <1. mofloomm poom Swab wo .oz .omMMSQUO coog zofins cw asap sopwssmmsm mo pcmohmm .m< mHQwB Om.H II II II O I: II II mmeom anm mm.O I: O an In H OH OH mammeom m0.00 OOH OOH ms HO OO OO OOH assopmxb ®®.@O OOH OOH HO HO OO OOH OOH derQO O0.00 OOH OOH HO OOH OO OOH OO OOHOQOHoho Hm.Om II OH Om em OH 1: OO mspmmsoomNN mm.O II O II II Om II II OOHocmHmO mm.H® OOH mO mm MO OO OO ON OSQNW J0.0H 1| 1| em sm :1 In I: GEomossOOOHQ oo.mm 7. sm em Hm om om cm eeHoeHeessssm mm.mH I: OH II II om O: II dwsxmdm Om.mO OOH m: :O OH O: Om OO mememm OHSOQOQ OO.: I: O O O In I: II sssnopmmq OO.: In I: O OH I: In In mswpsmuosm mo.sH I: O 6 ms oH OH 7: mssssoswxb momm HHO 7> om mO< >H mm< HHH mm< HH mO< H mO< O ow< moHommm Ooom m OH HH HH OH OH OH SOHO %0 .OZ .Omnhdooo Ooom QUHAS CH anMOHom Ho pcoosmm .>< OHQOB 39 IIII HO. IIII IIII IIII whomeom mm.mH sm.w mm. em.H mm. msssOsOs -- mm.sH -- Hm.s mo.H seesmsm -- Om. Hm.m Hs.m me.mH sHHOQOHeso -- -- ms.O we.o ms.H seHoseHso om.H NO.OH mm.m om.ms om.mm ssssasm ma.se sw.ms ms.m ss.ms mo.sm sssssssss ms.m -- Hm. em.H om.m wsewsssssm mm.OH Os.mH ms.wm Om.mm om.mm assessssss mESHo> O madHo> R mesHo> w mssHo> O mssHo> R mmHommm so Hm-om as m.mH-eH so m.mH-mH as m.sH-HH so m.OH-m.s mmssm semssq eoos e O s om mm sees no .oz >H HHH HH H o mmsHo ems .Anopmm BOHHmhv mmmHo mmm hp smpmm mEmHsmOso Ooom HHw mo maSHo> psmosmm .O¢ mHnmE hO Table A9. Percent volume of all food organisms eaten by age class (white bass). Age Class O I No. of Fish 22 15 Length Range 6.5-12.5 cm l3—23.5 cm Food Species % Volume % Volume Chironomus 21.5h __-- Procladius 10.38 _-__ Leptodora 65-83 78.77 Daphnia ephippia .02 _--- Daphnia 1.hl .87 Ceriodaphnia .Ol __-_ Alana -——- _--_ Calanoida .1h .01 IZyocryptus —--— _-__ Cyclopoida .66 12.52 Bosmina .03 2.63 Chydorus .02 h.31 Rotifera -—-- .89 hl l-ll llll llll OO.H ll-l mxsopmxb lll- llll llll Hz. NO. Uswsmom OH. llll llll HO.H mm.w OOHOQOHomO llll llll llll OO. llll GSQNW llll llll llll llll HO. BEomQKUOOOOQ HO. NO. On. OO.H HO. UOOOOUQ llll llll llll OO.H llll «HmmHsmm UOEQOOQ 2m.gm Hm.Om OO.mm Om.m: O:.O Gsopoummq OH.MH :O.m mm.MH mO. Hm.m mxwfidmbokm OH.mm m0.0m O4.0m O0.0m H0.0~ mssososwxb mESHo> O msdHo> O madHo> O mESHo> O mssHo> O mmHommm Eu Omlm.sm Eu :mle So m.OmlOH Eo m.~HlHH Eu m.OHlm.: mwsmm SHOEOH Ooom O OH OH mm ON anm mo .02 s-E HE S H Q was 8 8.4 .AESLO sopwsnmmsmv mmeo mwm mp cmpmm mEchmOso Ooow HHw mo mEdHn> pcmosmm .OH< mHQmB 142 llll llll llll Illl mo. llll msmmeom om.sm Om.m OH.m No.mm HO.OH mm.mm sssowsxu m.oH mo.s mm.cH ~m.mH ss.w NO.H ssOsmsm OH.Om OO.H: mm.mm m:.>m H:.m: OO.mm OOHOQOHUOO mm. OO.H m4. mo. -- mm. assasssomHHH Os. -- -- ms.m -- -- seHostwo mm.H OO.: es.m ms.m OO.: wo.m sesHs mO. OO.H OO.H -- lll- l-ll sEomossxmswq mO. OO. NO. OH. Om. llll OOHOOHpommswm mm.m -- -- mO.m OH.H OO. sws£asq . mo.oH m~.mH om.Om sp.» ss.sH no.0 eHssHssm swsxmsq ms.> Om.O Om.m -- -- -- ssswssasH -- Om.m OO.N -- -- -- msOOsHsosm No.3 om.m mo.mH OH. OH.@ -- msssssswxu mEdHo> O mfizHo> O mEdHo> O mESHo> O OESHo> O mESHo> O mmHommm so Hm-m.Om as Om-Om so O.mm-mm so m.sm-m.mm as mm-mH s6 m.OH-m.OH mwssm semsmH seem NH OH mH m a O smHa Ho .oz > >H HHH HH H o mmeHo mw< .AanMOHomv mmeo mmw an cmpmm mEchwwso Ooom HHm go madHo> pcwosmm .HH< oHnt mo. -- ms.H mo. ssmmHsom HO.OH -- OH.~ mm.» msssOOHO Om.O llll Hm.: OO.NH dzwsmom Hm.m: Hoo. ms.om as. seHOQOHeso llll llll llll mm. msummsucmma OO.m llll Illl llll GEQNQ Om. llll Illl llll mcHooHpommsmm OH.: OO. em. m».m svsxmsm 4 ON.OH llll llll Illl meQHzmm BOSOQOQ Hm -- sm.mm mo.mw mm.mb ssswssmsH mesHo> O mESHo> O oESHo> O mESHo> O mmHommm poOlOS< Os Osmosmm .oH¢ memB Table A15. Mean annual electivity index for four species of fish. Food Species Goldfish Sheepshead White Bass Yellow Perch Leptodora - 58 +.62 +.6h +.71 Daphnia* -.89 -.63 —.82 —.13 Harpacticoida +1.0 ---- -—-— —l.0 Calanoida -.79 -.98 -.98 +.12 Cyclopoida +.fl) +.O6 -.32 +.26 Bosmina* —.32 -.96 -.73 -.M2 Chydorus* -.O7 -.89 —.66 -.07 Rotifera -.99 -l.0 -.98 —.99 Not found in water Daphnia ephippia +1.0 +1.0 +1.0 +1.0 NCA; fourui in fish Nauplii -1.0 —1.0 -1.0 -l.O Rare Ilyocrgptus +1.0 -——— -—-- +1.0 Rare Diaphanosoma -.37 -l.O -1.0 -l.O Rare Ceriodaphnia ———- -——— +1.0 ---— Not ident. in water at all Alana +1.0 +1.0 +1.0 --—- *Found in both stomachs and water. l9?! ---- l972 L H .' PV 7 YELLOW PERCH g I z D I b a D < P 0 i (D . 3 t g - 9 -_- o----o--- .0. I n o b 9.8 R +.6\: 9 . .4\h O Q 2\P z . “I < O— _.' -.2-—"" < '.4;: Oq O -.6 l- ” \ O----0----- ,gib 0'"‘°'"'M 9 I 3 ; o----o-----q R 0 I: ‘\ I \ >- _ \ I \ o P \‘ ’ \ q v--v----c--v- .'8 . m ..°\- 0 9.4-\: 8 . 2‘1- '_ O—. a -.2-—-- DJ - ,4/: J --B/' o- -.8-/’ -|.0-/ .Moyb 'Jun6 July? A098 80939 Oct l0 “0’5 Jun 6 July? A098 SONS 01:th l73ll428 l2262l630l327 ll 25 I7 3||428 I2 923 204m I02472l 5l9 923 6204M 302472| 5|9 2|630|327l|25 Figure A. 16. Electivity index (Ivlev, 1960) for yellow perch. DIAPHASOMA ROTIF ERA I LLYOCRYPTUS BOSMINA O FRESHWMTER DRUM o I97l ---- I972 I DAPH. EPHIPPIA I '0 Vi I V! I I I I I I I o-«o----o----o--od ‘3 DAPHNIA ‘0 Q N 1 ALONA I T'UUV‘I'U'V CALANOID 9 9 I I ’9 ‘v DIAPHASOMA O IIIIII11III CYCLOPOID V '\ U I'f' I I I I BOSMINA ' 9|.°\ 2. 20-“ ::3\ ’I “b-----d” . A: 9’ - I: d O LEPTODORA CHYDORUS TUV‘V'UUVIV Aug 8 2330 923 309' 9 069 I0 IS "25 620 4“ 00900 4 IO "25 A098 80909 923 620 2|6 l327 7 2| l9 I42 l2” l4 2. I226 72! BIG Jun Barfly 7 Jun 6 Fab 7 Figure A. 18. Electivity index (Ivlev, 1960) for Freshwater drum. wMINA o--o----oo----o- o-o-o QHYDORQ§ 149 WHITE BASS ——|97I ---- I972 *- 0000 “11.1 9 4 3 9 ‘i’ I‘VUI'UI'TV = A .9 s : . Z . I E ; o-o-ouo-o- -o--- < .. O - o .0 _ Q o .O-§. 9 8 . 4\. l, . '2‘: g 3 0—1- I o - 2" ' >- - A" ' o o’o- " .C/I- ' O--0----Oov’ -o - .../F wove-OW é? 3. : o \ I b’ :cr1rcrqr<\ F . ‘W\ 35 P . -J I D ‘W ll Figure A. 17. M6 JuIyT Ange WOMIO “016 MO JuIyT Aug! :05" I4 1226923 2040 II I420l2m emu 4I0 72I I9 2B I327 II25 2| 30I32T II Electivity index (Ivlev, 1960) for white bass. DAPHNIA EPHIPPIA ALONA CALANOID DIAPHASOMA 50 GOLDFISH «1 ? p /Q LEPTODORA CYCLOPOID O 'I'Uil'UI'I ‘( CALANOID HARPACTICOID 9 l i O I I I I I ! I I I I I 9 I I I ‘3 q 0 DAPHNIA r I'Y‘U'ITIVT DIAPHASOMA q I BOSMINA \ I I I I I! I I I I I ILLYOCRYPTUS Won-so .../. O l ALONA \ ...o bv‘ I. lawz‘aAquLSom OcIIONov ll Docr’ei I9 I6 l3 ll 25I I5 l3 I2 9 23 20 4 I8 8 20 ' 20 Figure A. 19. Electivity index (Ivlev, 1960) for goldfish. CHYDORUS TUITI Jul? Aug 8 Sept Oct Nov II DocI 5I92l6 I327II25822620 I2 9 23 20 IS I I5 I3 HICHIGQN STATE UNIV. LIBRQRIES I II III II IWII l 8 1917 312930084