LIBRARY lllllllll ll 2\\1\3 3 Megan m This is to certify that the thesis entitled THE SELECTIVE FEEDING 0F IMMATURE BLUEGILLS (LEPOMIS MACHROCHIRUS) AND BROOK SILVERSIDES (LABIDESTHES SICCULUS) ON THE ZOOPLANKTON 0F GULL LAKE, MICHIGAN presented by Roger William Ovink has been accepted towards fulfillment of the requirements for Master_o_f_Sc_i_enne_degree in EijhaLLesJ; Wildlife ajor professor Date 21 February 1978 0-7 639 1‘. 2 :3. 19:3 w“. 9' ‘k‘; Al ."1. ‘_ ‘_ __.__ THE SELECTIVE FEEDING OF IMMATURE BLUEGILLS (LEPOMIS MACHROCHIRUS) AND BROOK SILVERSIDES (LABIDESTHES SICCULUS) ON THE ZOOPLANKTON 0F GULL LAKE, MICHIGAN By Roger William Ovink 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 1978 ABSTRACT THE SELECTIVE FEEDING or IMMATURE BLUEGILLS (LEPOMIS MACHROCHIRUS) AND BROOK SILVERSIDES (LABIDESTHES SICCULUS) ON THE ZOOPLANKTON or GULL LAKE, MICHIGAN By Roger William Ovink Immature bluegills (Lepomis machrochirus) and brook silversides (Labidesthes sicculus) migrate to the limnetic epilimnion from the littoral zone of Gull Lake, Michigan, in the summer. They remain for approximately seven weeks and then return to the littoral zone. The apparent spatial overlap between the fish, both in the littoral and limnetic zones suggests that a feeding overlap may exist. In an effort to determine whether a feeding overlap occurred while they coinhabited the limnetic epilimnion of Gull Lake, immature bluegills and brook silversides, as well as zooplankton, were sampled on a weekly, diel basis from August 8 through September 19, 197A. The results indicate that no major feeding overlap occurred. Bluegills consumed prey mainly from the 0.5-1.0 mm (Cyclops spp. and Diaptomus spp.) and 1.0-2.0 mm (Daphnia 222;) size classes while brook silversides consumed prey mainly from the greater than 2.0 mm size class (Chaoborus Spp., Leptodora kindtii and adult Diptera). To Jennifer, with much love. ACKNOWLEDGMENTS I wish to thank Dr. George Lauff, Dr. Patricia Lane, Dr. Eugene Roelofs and Dr. Howard Johnson for their advice and support. I also wish to thank Sam Jackman for his help during the sampling and processing periods of this project. Funding was provided by NSF Grant 63-3337 (Levins, Lane and Lauff). TABLE OF CONTENTS Page LIST OF TABLES. . . . . . . . . . . . . . . . . . . . . . . . . . v LIST OF FIGURES . . . . . . . . . . . . . . . . . . . . . . . . . vii INTRODUCTION. . . . . . . . . . . . . . . . . . . . . . . . . . . I METHODS AND MATERIALS . 3 RESULTS AND DISCUSSION. . . . . . . . . . . . . . . . . . . . . . 8 Prey size class densities in the water column. . . . . 8 Bluegill predation . . . . . . . . . . . . . . . . . . . . 8 Brook silverside predation . . . . . . IS A comparison of bluegill and brook silverside predation. . . I9 SUMMARY AND CONCLUSIONS . . . . . . . . . . . . . . . . . . . . . 25 APPENDIX. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 LIST OF REFERENCES. . . . . . . . . . . . . . . . . . . . . . . . 36 Table 10. ll. LIST OF TABLES Prey size classes. . . . . . . . . . . . . . . . . . . . . . Results of single classification analysis of variance for mean prey size class densities among sample stations on the same sample date . . . . . . . . . . . . . . . . . . . . . . Results of single classification analysis of variance for mean prey size class densities among sample dates. . Results of single classification analysis of variance for bluegill predation on different prey size classes among sample dates . . . . . . . . . . . . . . . . . . . . . . . . Bluegill predation.* A summary of single classification analysis of variance results between the mean densities of pairs of prey size classes found in the gut content on each sample date. . . . . . . . . . . . . . . . . . . . . . Bluegill electivity indices (based on mean prey size class densities in the gut contents and in the water column for each sample date). . . . . . . . . . . . . . . . . . Product-moment correlation coefficients for bluegills and brook silversides (correlating mean prey size class densities in the gut content with mean prey size class densities in the water column over sample dates) . . . Results of single classification analysis of variance for brook silverside predation on different prey size classes among sample dates . . . . . . . . . . . . . . . . . . Brook silverside predation.* A summary of single classification analysis of variance results between the mean densities of pairs of prey size classes found in the gut content on each sample date. . . . . . . . . . . Brook silverside electivity indices (based on mean prey size class densities found in the gut contents and in the water column for each sample date) . . . . . . . . . . . . Bluegill (BG) - Brook silverside (BS) predation.* A summary of single classification analysis of variance results between the mean densities of prey size classes found in the gut content of the two fish species for each sample date . Page IO 13 14 l6 I7 18 20 21 23 Table Page 12. Capture, length, weight and gut content data for bluegills. . . . . . . . . . . . . . . . . . . . . . . . . . 26 13. Capture, length, weight and gut content data for brook silversides. . . . . . . . . . . . . . . . . . . . . . . . . 31 vi LIST OF FIGURES Figure Page 1. Sample sites on Gull Lake. . . . . . . . . . . . . . . . . . A 2. Mean prey size class densities/cubic meter in the epilimnion of Gull Lake during day and night sampling periods . . . . . 11 Mean zooplankton population densities/cubic meter in the epilimnion of Gull Lake during day and night sampling periods. . . . . . . . . . . . . . 12 vii INTRODUCTION Competition for food between animal species is common in most ecosystems. Fish fry are especially vulnerable to both interspecific and intraspecific competition for food (Werner, 1977). Survival rates of larval fishes are extremely low. Competition for food could be a major contributing factor in the high mortality rates of immature fish. Reducing this competition occurs in a variety of ways. Size selective predation (Werner, 1977; Werner, 1969), habitat selection (Werner and Hall, 1976; Werner, et al., 1977) and niche flexibility (Werner and Hall, 197A) have been presented as possible factors minimizing competition for food in freshwater sunfish. The migration of fish from the littoral zone to the limnetic zone in lakes (Hubbs, 1921; Werner, 1969) may also serve to reduce competition for food among immature fish species. A variety of fish fry, including sculpins (Heard, 1965), sockeye salmon (McCart, 1967), yellow perch, black crappie (Faber, 1965), bluegill (Faber, 1965; Werner, 1969) and brook silversides (Hubbs, 1921) have been shown to migrate from the littoral zone to the limnetic zone of lakes following yolk sac absorption. Pennak (1966) noted that much higher concentrations of 200plankton occurred in the limnetic zone than in the littoral zone of some Colorado lakes. In that zooplankton serve as a main food item for many immature fish species, the greater abundance of zooplankton in the limnetic zone may help to reduce interspecific and intraspecific competition for this food source. Immature bluegills have been found to migrate from the littoral zone to the limnetic zone in the summer, where they remain for several 1 weeks and then return to the littoral zone (Werner, 1969). Bluegills have also been noted to: feed almost exclusively on zooplankton (Baumann and Kitchell, 197A); feed almost continually throughout the day and night, consuming whatever is most active (Keast and Welsh, 1968); feed size selectively (Werner and Hall, 197A) and feed mainly on insects when they reach maturity (Gerking, 1962). Immature brook silversides migrate to the limnetic zone from the littoral zone in the summer, remain for several weeks and return to the littoral zone (Hubbs, 1921; Keast and Webb, 1966); feed on whatever zooplankton are most abundant (Mullen, Applegate and Rainwater, 1968) and feed almost exclusively on insects when mature (Hubbs, 1921; Mullen, Applegate and Rainwater, 1968). Considering the above information, it is evident that a major feeding overlap could exist both in the littoral and limnetic zones of lakes where these species coexist, and that the growth and development of one or both Species could be impaired. The feeding dynamics of the two fish species were studied during their coexistence in the limnetic epilimnion of Gull Lake, Michigan, to determine whether a major feeding overlap occurred between them and if an overlap did occur, how it affected the immature bluegills and brook silversides. METHODS AND MATERIALS The limnetic epilimnion of Gull Lake was sampled for zooplankton and immature fish from August 8 through September 19, 197A, on a weekly, diel basis. Gull Lake is located in Barry (T.1N., R.9-10 W., Sections 31, 36) and Kalamazoo (T.IS., R.9-10 W., Sections 6, 7, 8, 17, 18, 20, 1, 2, 12) counties in southwestern Michigan. It is a hardwater lake, glacial in origin, with a surface area of 820 hectares and a maximum depth of 33 meters. Immature fish were sampled at three stations (Figure 1) with a lift net, 3.0 meters square, constructed from conduit pipe and 3.0 mm nylon netting. The net was lowered into the lake to a depth of three meters. Gas lanterns were then directed over the net until numerous fish were attracted. The net was then lifted capturing them. The fish were removed and preserved in a five percent formalin solution. All fish were captured between 10:00 p.m. and 1:00 a.m.; no fish were captured during daylight hours. Zooplankton samples were taken at 0, S, and 10 meter depths at three stations by one of two methods. The first method was to tow a Clark-Bumpus plankton sampler equipped with a 0.018 mm mesh plankton net for two minutes at each depth (thus, filtering between 700 and 1000 liters of water). The second method involved taking triplicate, eight-liter samples with a modified Van Dorn water bottle from each depth and filtering the zooplankton out with a 0.018 mm mesh sieve. The second method was employed only when the Clark-Bumpus plankton sampler was not functional (August 8, 15). The zooplankton samples were 3 eofiuoum nuaom oxen fiasu :0 «mafia oaaaum .~ ounwwm cofiuuum annuaoo acauoum auuwwoaowm o wmoAAHx .x.3 noduoum suuoz preserved in a four percent sucrose-formalin solution (Haney and Hall, 1973). All zooplankton samples were taken between 10:00 a.m. and 1:00 p.m., and 10:00 p.m. and 1:00 a.m. The fish were identified to species, weighed to the nearest .01 gram and measured to the nearest 1.0 mm (for total and standard lengths). The length and weight measurements were corrected for the effects of formalin preservation (Parker, 1963). Gut analyses involved cutting the fish ventrally from the lower jaw to the anus and removing the entire viscera with a spatula. The stomach and foregut were then isolated and their contents were usually identified to genus and enumerated using a Wild dissecting microscope at ZSOX magnification. The prey were measured with an ocular micrometer to the nearest .01 mm and were separated into five size classes (Table 1). Duplicate, 0.3 ml sub-samples were taken from the zooplankton samples. The zooplankton were usually identified to genus and enumerated using a Wild dissecting microscope at 250x magnification (except Chaoborus gpp;_and Leptodora kindtii which were counted in total). Zooplankton densities per cubic meter were then calculated for each station-depth and date. Data analyses included the calculation of electivity indices (Ivlev, 1961), single classification analysis of variance (Sokal and Rohlf, 1969) and product-moment correlation coefficients (Sokal and Rohlf, 1969). The electivity indices were calculated using mean prey size class densities in the water column and in the gut contents of the fish for each sample date to determine whether the immature bluegills and brook silversides actively selected any of the prey size classes. Since fish samples were taken at night (between 10:00 p.m. and 1:00 a.m.), the prey __upc_x mLoUOummmemcuua_o u_:nm u.amw wagonOmcu EE o.~x 5:; 253% E o.~-o._ .mmmlmaeouam_o “.mmw ago—mxu EE o.—Im.o .aam mc_Em0m EE m.oI~.o ___Q:mc toaoq0u EE ~.ov came >oc¢ mmm_o o~_m mommm_o o~_m >ocm ._ o.nmp size class densities used from the water column were mean values for each size class from the night sampling periods. Single classification analysis of variance was used to determine whether significant* differences existed in the mean prey size class densities in the water column among sample stations or among sample dates. The size class densities in the fish gut contents were also analyzed to determine whether significant variance existed among size class densities on the same sample date, among densities of each size class on different sample dates, between densities of size class pairs on the same sample date, or between the gut content of each fish species on the same sample date. Mean densities for the size classes in the gut contents were used in these analyses. Product-moment correlation coefficients were calculated with respect to the mean prey size class densities in the water column and in the gut contents of each fish species. The size class densities used in the calculations were mean values for each prey size class from the night sampling periods. Planktivoirous fish are known to follow the vertical migrations of zooplankton in lakes (Narver, 1970; Johnson, personal communication). Brook silversides and bluegills feed continuously through the day and night and undoubtedly follow their zooplankton prey deeper in the water column during the day and then return with them to the surface at night. The data discussed herein were collected at night but the general behavioral and forage patterns of planktivoirous fish suggest that the predator-prey relationship probably would remain the same over a twenty- four hour period. *Unless otherwise indicated, all significance referred to will be at the 0.05 confidence level or above. RESULTS AND DISCUSSION Prey size class densities in the water column The mean densities for each size class were not significantly different among sample stations for any sample date (Table 2). Thus, there were no concentrated prey communities at any of the sample stations during any of the sample dates, and the limnetic epilimnion of Gull Lake was essentially homogeneous, in terms of the prey size class densities. The mean densities for several of the size classes varied significantly among sample dates (Table 3). Significant density variations occurred in the <0.2 mm, 0.5-1.0 mm and the 1.0-2.0 mm size classes. This variation among sample dates may be attributed to the periodic I'pulsing” of different zooplankton genera in lakes in response to certain parameters (light, temperature, oxygen concentration, food availability, etc.) causing the rapid development of their immature stages thereby initiating a sudden population increase (for more prey density information see Figures 2 and 3). Bluegillgpredation There was significant variation in the frequencies of predation upon several of the prey size classes among sample dates (Table A).' Significant differences occurred in predation on the <0.2 mm, 0.2-0.5 mm, 0.5-1.0 mm and 1.0-2.0 mm size classes. Frequencies of occurrence in the gut content of the various prey size classes also varied significantly on several sample dates (Table 5). The 0.5-1.0 mm size class was consumed significantly more often than any other on August 8, August 29 and September 19. The 1.0-2.0 mm size class was consumed 8 o>onm Lo mo.o um unmo_m_cm_m ac: u m: o>onm Lo mo.o um acmo_m_cm_m u « -.~ n m .mu_u_cu :o.umum m: m: m: m: m: m: m: . x as o.~x me m: m: m: me me me co_umum x as o.~Io._ m: m: m: m: m: m: m: co_umum x as o._Im.o m: m: m: m: m: m: m: co_umHm x as m.oI~.o m: m: m: m: m: m: m: co_umum x as ~.ov .uaow .uaom .uaom umama< umama< um3m3< umsm3< co_um_cm> m. o. m mu Nu m. m mo ooL30m .oump o_aEmm osmm may :0 mco_umum o_aEmm macaw mo_u_mcou mmm_o o~_m >uea some Lo» oucm_cm> mo m_m>_mcm co_umu_m_mmm_u a.mc_m mo mu_:mox .N o_nmh lO o>0nm Lo mo.o um ucmo_m_cm_m uoc u m: o>onm Lo mo.o um acmo_u_cm_m n « n~.~ u u .mo_u_cu . . . pump mcuw o mo. x o m o :o. x o w x as o.~A . . oumu x . x x . +mm N mo. o m 0 mo. w a as o.~uo._ . . . pump x «NA o. mo. x o m m o_o_ x o m as o._-m.o mum mcm_._ mo. x m.~ o No. x N._ as m.o-m.m . . . oumv «mm N wo— x : _ o mo_ x : m x as ~.ov u_um_umum I m mocmacm to scoop.» mocmzcm :o_um_cm> Esm cmoz mo moocmoo mo Eam mo ooL30m o~_m >uca came .moumu o_QEmm macaw momu_mcou mam—o Lo» oucm_cm> mo m_m>_mcm eo_umo_w_mmm_u o_mc_m mo mu_:mo¢ .m m_amh (0.2 - 13 2 I A a A >. 13 s 3 a 0 0 I I I I :3 u :3 .. :3 =2:- 9 g S I: ‘3 1 fit V f v v v 2 V V V V V V fi 0 15 22 29 5 10 I9 15 22 29 5 lo 19 August Sender August Ssptdss 0.5 - 1.0- 1.0-2.0- 80} ”A HA h A h o . '2: . u- g d '0 I 0 . 0 o u I: .. :3 u "" : a a g S? g . '0 V v f V fl 1 t“. 33 ‘ V v 17 V V fl 0 19 22 29 5 lo 1 0 15 22 29 S to 19 August 39999.5“ August Sept“ ZlJUl! 34 ~:: -—~ .- v 5 . o s d U U '6 f. g: 3 v i v v v ‘1 0 13 22 29 5 10 19 August Septubss Figure 2. Mean prey size class densities/cubic meter in the epilimnion of Gull Lake during day and night sampling periods. 12 Copspod nauplii .— U A Densities (x 103) night 0 day 13 ' ‘ f t V F O 15 22 29 5 10 19 August Ssptdes Englayn 331 «16% day 0 Donsitics night .\ U U «Ian day 0 s- A I Densities night Densities night I k Tb Supt-bur «16% day 0 2 mg:- 1:: '9'. 5 W a o — 3 W as ‘6 cs 3. 2 1 f 1 r s T I 0 i 22 29 5 10 19 August aunts-bot mtindtii aw — A 1:? -u-I 5 WW . 01_ '0‘ I ass '3'? 83 3 1 T I O 15 22 29 5 i0 19 August Seuss-hot gmhnaaub 33‘ and” day 0 U U .1 ps U N N N 0 U p O s.- U nisgtonus £23. Densities night ’ N ‘_._ s 13 Figure 3. 1 fl is 5 10 is Septnnth Mean zooplankton population densities/cubic meter in the epilimnion of Gull Lake during day and night sampling periods. 13 o>onm Lo mo.o um acmo_m_cm_m yo: me m>oam co mo.o um acmu_m_cm_m n « m_.~ n u .mo_u_cu 28.0 86 e 85 x as “me .oo.m m~.-~ a om.mmm_ as owwwm.“ ._o.__ mm.kmes m oo.s~mk~ as ow”wm.w «mo.e, mm.mem e mm.om_~ as mwwwm.m Esm.s me.m_ a om._m x as Mwmm u_um_umum I m nonmaam mo sonoocw mocm3Um co_um_cm> Sam emu: $0 moocmoo mo 53m mo ouc30w .moumu u_aEmm macaw mommm_u o~_m >oca acocomw_u co co_umvoca ___mo:_n Lo» oucm_cm> mo m_m>_mcm :o_umo_m_mmm_o a.mc_m mo mu_:mom J 253 1h .oumu away :0 mmm_u u~_m cacao >cm cmcu coumo once >_ucmo_m_cm_m nosamcoo uo: mm: mmm_u o~_m m umzu moumo_uc_ me use “pump umcu co — vo_onm_ mommm_u o~_m omo;u mm :uumo mm no: use me um_onm_ momma—u o~_m mmo;u cmgu coumo ocoe >_ucmo_m_cm_m cesamcou mm: mmm_o m~_m m umzu moumu_nc_ N “sump umcu co mmm_u o~_m Lucuo >cm coca coumo egos >_ucmo_w_cmwm cesamcou mm: mmm_o o~_m >oca m umzu moumu_uc_ _ .oumu o_aEmm Lm_:u_ucma m cos : _ e m: 8 m 3 29:32... E m: m: m: me me me me as o.NA N m: _ N N m: N as o.NIo._ — m: m: — N m: — EE o._Im.o N m: m: m: m: me me ES m.oIN.o me m: m: m: m: m: N as N.ov .uaom .uaom .uaom umama< umama< um3m3< um3m3< mmm_o o~_m m— o. m mN NN m— m .oumn o_aEmm some :0 ucuucou uzm ozu c_ peso; mommm_o o~_m >oca mo mc_ma mo mo_u_m:op some on» couzuon mu_:moc oocm_cm> mo m_m>_mcm co_umo_u_mmm_o p.mc_m mo >LmEE:m < «.co_umuoca ___mo:_m .m o_nmh 15 significantly more often than any other on September 5. Generally, the 0.5-1.0 mm size claSs was preyed upon significantly more often than the other size classes (Table 6). The results indicate that the immature bluegills fed upon the 0.5-1.0 mm and 1.0-2.0 mm size classes with relation to their abundance while they selected against the <0.2 mm, 0.2-0.5 mm and >2.0 mm prey size classes. The product-moment correlation coefficients (Table 7) indicate that a significant relationship existed between the 1.0-2.0 mm prey size class densities found in their gut contents and those found in the water column. A strong (though not significant) relationship was also indicated between the gut content and water column prey size class densities for the 0.5-1.0 mm size class. The electivity indices and the correlation coefficients indicate, therefore, that the immature bluegills preyed mainly upon the most abundant prey size classes. The bluegill predation results concur with the literature in that they were found to feed exclusively on zooplankton (Baumann and Kitchell, 197A) with the crustacean planktors being their most selected prey (Werner, 1969). Further, their predation was size selective (Werner and Hall, 197%; Werner, 1969). The variability in the electivity indices (Table 6) through the sampling period may be attributed, in part, to the behavioral flexibility of bluegills (Werner and Hall, 197A) which enables them to better utilize their available food resources. Brook silversides predation Significant variation among sample dates occurred concerning two of the prey size classes (Table 8). Brook silversides gut content counts varied significantly with respect to the 1.0-2.0 mm and the greater than 2.0 mm size classes. Frequencies of occurrence of the prey size classes 16 om.oI oo._u oo._I oo._n oo._u mm.o+ oc._I oo... 55 o.NA No.o+ mo.o+ mo.o+ :m.o+ m_.o+ Nm.o+ mm.o+ N:.ou es o.NIo._ $0.0- NN.o+ NN.o+ _:.ou _o.o+ o_.oI co..- mo.o+ EE o._Im.o mm.oI _N.o+ Fn.o+ oo._I om.oI oo.o co..- oo... 55 m.oIN.o pm.ou oo._I oo._I oo.—I mm.ou oo.—I co..- 4m.o+ EE N.ov cams .uaom .uaom .uaom umams< umama< umzm3< umama< mmm_u o~_m nou;m_mz __mLo>o m. o. m m~ NN m. m new mucoucoo Ham ozu .Aoump o_asmm comm ecu ass—00 Loam: ozu c_ c. mo_u_mcov mmm_o o~_m >uca came :0 nommnv moo_pc_ >u_>_uoo_o ___mo:_m .o m_nmp mo.o u m l7 oo.m H mo mm.o u m .mo_u_cu mp. 00. EE o.Nx .m. Na. 58 o.NIo._ om. no. es o._Im.o mm. mo. 55 m.oIN.o @J. @m. F3: N.CV mop_mco>__m xooLm ;m_mc:m ___mo:_m awn—o o~_m .Amoumv o_qum co>o can—Co Loam: ozu :_ mo_u_mcou mmm_o o~_m >uca cmoe ;u_3 acmucou Ham ocu c_ mu_u_mcon mmm_u o~_m >oca came m:_um_occoov mon_mcu>__m xooLn new m___mm:_n Lo» muco_o_mmuou :o_um_occoo ucuEOEquanoL¢ .N o_nmh 18 o>onm Lo mo.o um ucmo_m_:m_m no: me u>onm Lo mo.o um acmo_m_cm_m u « m_.N n u .mo_u_cu . . . mum EN: awe mm com o oo moms x as o.~m . . . pump x «.N m . mo :mw m an :mmm EE o.NIo._ . . . mum mcmm _ we .kk a 00 one; as o._-m.w . . . oumu x mc_m o em _ o m. __ EE m.oIN.o . . . Home mcmN o mm m. m ON _o_ x as N.ov o_um_umum I u mocmsom mo EOpooLm mocmaom co_um_cm> Enm cmoz mo moocmoa mo Eam mo ouL30m .moumu o_aEmm macaw mommm_o o~_m >oca acocomm_u co co_umpoca on_mco>__m xooLn Lo» oocm_cm> mo m_m>_mcm co_umo_m_mmm_u a.mc_m mo mu_:mo¢ .m o.am# 19 in the gut content varied significantly on several dates (Table 9). On September 19, the 0.5-1.0 mm size class was consumed significantly more often than all other size classes. On August 22 and August 29 the greater than 2.0 mm size class was consumed significantly more often than all other prey sizes. Generally, the greater than 2.0 mm size class was preyed upon significantly more often than the other prey size classes. Immature brook silversides were size selective predators. Their prey were generally from the largest, least abundant size class (>2.0 mm). The electivity indices (Table 10) indicate that they selected most strongly for the greater than 2.0 mm size class. A further indication of their selective ability is presented in the product-moment correlation analyses (Table 7). No significant relationship was indicated between they prey size class densities found in their gut content and those found in the water column. A significant relationship between the two densities would suggest that they were consuming the most abundant prey. No significant relationships, therefore, suggest that the brook silversides were feeding selectively. The brook silverside predation results both agreed and conflicted with the literature. They fed almost exclusively on zooplankton (Hubbs, 1921) but they were not found to feed on the most abundant zooplankton (Mullen, Applegate and Rainwater, 1968). On the contrary, the brook silversides preyed mainly upon the least abundant zooplankton and insects (>2.0 mm size class) throughout the sampling period. A comparison of bluegill and brook silverside predation A major feeding overlap did not occur despite the apparent spatial overlap of the two fish species. Bluegills consumed significantly more of the 1.0-2.0 mm and 0.5-1.0 mm size classes than did brook silversides 20 .mmm_o o~_m Locuo >cm cmcu couwo ocoe >_ucmu_m_cm_m cesamcoo yo: mm: mmm_u o~_m >oca m umzu moumo_uc_ m: “N Lo — no_onm_ umOcu mm coumo mm no: use me uo_onm_ mommm_o m~_m omega cmcu coumo ocoe >_ucmu_m_cm_m cesamcou mm; mmm_u m~_m m umcu moumowuc_ m up uu_onm_ omega mm couwo mm yo: use me ucm m uo_oam_ mommm_o o~_m omozu cmcu coumo egos >_ucmu_w_cm_m possmcoo mm: mmm_o o~_m m umcu moumo_uc_ N "mmm_o o~_m Lozuo >cm cmzu coumo ocoe >_ucmomm_cm_m unsamcoo mm: mmm_u o~_m m umzu moumo_nc_ _ .oumu o_aEmm Lm_:o_ucma m co« s. MN mm mN m m m m_a2mm\;m_a N me me p p m: m: as o.NA m m: m: N N m: m: as o.NIo._ — me m: m m: m: me SE o._Im.o m: m: m: m: m: we m: as m.oIN.o m: me m: m: m: m: m: as N.ov .uamm .uaom .uaom umama< um3m3< umama< um3m3< mmm_o o~_m m— o— m mN NN m_ m .oumv o_aEmm some :0 acmucoo yam may :_ peso» mommm_o u~_m >uca no mcmma mo mo_u_mcop cmoe any cuozuon mu_:moc oocm_cm> mo m_m>_mcm co_umo_m_mmm_u p.mc_m mo >LmEE:m < «.:o_umpoca ou_mco>__m xOOLm .m o_nmh 21 Nm.o+ mm.o+ om.o+ Nm.o+ mm.o+ mm.o+ mm.o+ mm.o+ es o.~x op.oI m—.o+ mm.o+ mm.oI m:.o+ mo.o+ m:.o+ mm.o+ EE o.NIo._ m_.oI No.oI mm.oI 0N.o+ mm.oI m_.OI oo._I —m.cI EE o._Im.o om.oI Nm.0I oo._I om.oI om.oI NN.oI oo._I oo._I ES m.oIN.o mw.0I mm.oI oo._I _:.oI oc.pI oo.—I oo.—I oo.—I EE N.ov come .uaom .uaom .uaom umzma< umama< um3m3< umama< mmm_u oN_m nou;m_oz __mLm>o m. o. m mN NN m. w .Aoump o_aEmm sumo LOm sea—ou Loam: ecu :_ ucm mucoucoo uam ozu c. peso» mo_u_mcon mmm_o oN_m >oca cmoE co vommnv moo_vc_ >u_>_uoo_o uc_mco>__m xooLm .c. o_nmh 22 (Table 11). Brook silversides preyed upon significantly more of the >2.0 mm size class than the bluegills (Table 11). It appears that a major feeding overlap between the fish species was prevented due to their different feeding habits. A recent study (Werner, et al., 1977) concerning the Centrarchidae indicated that habitat divisions aid in segregating fish species. This information may help explain the segregation of the immature bluegills and brook silversides. Brook silversides are generally found in the top twenty centimeters of the water column (Hubbs, 1921) while bluegills are generally located deeper in the water column (Werner, et al., 1977). Werner (1977) indicates that bluegills, with their compressed, short body shape and large pectoral fins are able to stop, turn and alter their vertical position in the water column readily but lack straightaway speed. They also have a small, highly protrusible mouth. This combination of abilities and structural features renders the bluegill very adept at capturing smaller, less mobile prey. The structural morphology of the brook silverside includes a narrow tubular body and dorso-terminal mouth with three rows of long, sharp, slightly retrocurved teeth. These features render the brook silverside highly mobile, enabling it to range widely over lakes and very adept at capturing surface insects (Keast and Webb, 1965). The growth rates of the two fish species differed greatly during the sampling period. The immature bluegills grew at a rate of 0.09 mmSL/day (0.001 g/day) while the brook silversides grew at a rate of 0.59 mmSL/day (0.017 g/day). These growth rate differences suggest probable metabolic rate differences between the fish species. The metabolic rate of the immature brook silversides would probably be 23 .mo_ooam ;m_w Locuo ecu cmcu noumu_nc_ mmm_u o~_m ozu mo ucoe >_ucmu_u_cm_m unsamcoo mo_ooam cm_w Locu_oc umzu moumo_vc_ me new mm___mo:_n u_v cmzu woumu_vc_ mmm_u u~_m ecu mo ocos >_ucmo_w_cm_m upEam:0o muv_mcu>__m xooLn umcu mmumo_uc_ mm “muv_mco>__m xooLn v.6 cmnu coumo mcoe >_ucmu_m_cm_m umumo_vc_ mmm_o o~_m any cesamcou m___mo:_n umzu moumo_pc_ om .oump o_asmm Lm_:o_ucmq m co« mm me me mm mm m: mm as o.NA m: m: mm mm am me me SE o.NIo._ cm on me m: m: m: mm as o..Im.o am m: m: m: mm m: m: as m.oIN.o me me m: m: m: m: m: as N.ov .uaom .uaom .uaom um3m3< umama< umama< umam3< mmm_o o~_m m— o— m mN NN m. w .oump u_aEmm sumo Lo» mo_ooam ;m_m ozu on“ mo acoucou yam onu :_ peso; momma—o o~_m >qu *0 mo_u_mcov cmoE ozu comzuon mu_:moc oucm_cm> mo m_m>_mcm co_umo_w_mmm_o a.mc_m mo >LmEE:m < «.co_umpoca Ammv op_mco>__m xooLm I Aomv ___mo:_m .__ o_nmh 2A greater than the bluegills, requiring the brook silversides to consume more food to provide energy necessary for their elevated growth rate. It would therefore be advantageous for the brook silversides to consume larger prey, acquiring more energy per food item. The different growth rates of the fish species (and probable metabolic rate differences) provide a partial explanation for their feeding differences. It is evident that the different feeding preferences of the two fish species was probably not the only factor preventing a major feeding overlap. Other contributing factors include possible segregation by habitat, the different structural morphologies of the two fish species and their different growth (and probable metabolic) rates. SUMMARY AND CONCLUSIONS Immature bluegills and brook silversides both occupy the limnetic epilimnion of Gull Lake for several weeks during the summer. The feeding dynamics of the two fish species were studied during their coexistence in the limnetic epilimnion to determine whether a feeding overlap resulted from an apparent spatial overlap. The fish and their potential prey were sampled at three stations from August 8 through September 19, 197A. Prey density counts and fish gut analyses were calculated to compare the feeding behavior of the two species. The following conclusions can be drawn from this study. 1. Mean prey size class densities did not differ significantly among the sample stations on the same sample date. 2. The mean densities of several of the prey size classes differed significantly among sample dates. 3. Bluegill predation was size selective, with prey from the 0.5- 1.0 mm and 1.0-2.0 mm size classes being consumed significantly more frequently than the other prey size classes. A. Brook silverside predation was size selective, with prey from the >2.0 mm size class being consumed significantly more often than the other prey size classes. 5. The apparent spatial overlap of the two fish species did not result in a major feeding overlap due to differences in prey selectivity, possible habitat segregation, and possible differences in the structural morphology of the two fish species. 25 APPENDIX 26 Table 12. Capture, length, weight and gut content data for bluegills. . GUT CONTENTS 5:: L m oi. as 5‘52... :: '3 o 113 E E 15 :3 '3 - . 3 L0 vvv — CO. in C 3+4 In'o Q...-Q1.ax. um 0c - . . :qamemo c Q‘U 4-00.: .1 u «Iago. o.‘ u 8 8 s...- .,; 3 castawae .. u UMI’OOLMED o o 3 o c ._ 'o o o 8 7.18 8858893: In E quolmum: m o o m o .c -- '0 U) UGO—100cm 1 8 Aug. N 16 14 .04 2 2 8 Aug. N 17 15 .05 7 I 3 8 Aug. N 19 16 .06 4 I 4 8 Aug. N 17 15 .05 2 1 5 8 Aug. N 16 13 .04 1 6 8 Aug. N 17 14 .05 7 8 Aug. N 21 17 .09 5 2 1 8 8 Aug. N 19 16 .07 2 1 9 8 Aug. N 18 15 .06 7 1 10 8 Aug. N I6 14 .05 2 II 8 Aug. N 18 15 .05 A 2 12 8 Aug. N 16 14 .04 1 13 8 Aug. S 16 14 .05 1 l4 8 Aug. 5 16 12 .05 2 1 15 8 Aug. S 13 10 .02 1 16 8 Aug. 5 17' 15 .05 I I7 8 Aug. 5 18 14 .05 I 18 8 Aug. C 17 15 .06 1 19 8 Aug. C 13 10 .02 20 8 Aug. C 18 15 .06 I 21 8 Aug. c 15 14 .0h I 22 8 Aug. C 18 15 .06 2 23 8 Aug. C 18 15 .06 2h 8 Aug. C 18 15 .07 2 A0 25 8 Aug. C 18 15 .06 5 39 26 8 Aug. C 18 15 .06 1 2 27 8 Aug. C 20 I6 .08 28 8 Aug. C 21 18 .09 2 79 29 8 Aug. C 18 I6 .06 2 1 3O 8 Aug. C 18 16 .06 3 31 8 Aug. C 18 16 .06 I 32 8 Aug. C 28 24 .27 I 22 33 8 Aug. C 20 17 .09 I 3 7I 34 8 Aug. C 19 16 .07 2 1 35 8 Aug. C 15 13 .04 1 187 36 8 Aug. C I7 14 .05 I 28 37 8 Aug. C 17 15 .05 A Table 12. (cont'd.) . GUT CONTENTS .CA EE 3 35:: ,A ,A z: '2 m 113 E E 15 :3 -§ . . 3L0.) vvv— C m =3: 88. . .3'6381'813 : o.'u .u m .4 .4 .u m 31 a, 81 u 88 2:59.53 =“mesw‘se .2251 BEE-8835" a. can 8' '5 .5 3 '8 .2 3. J: u) E o. m o. D. m U m 3 m o o m o .c >~ -- '0 ua e: a: c: .1 e: L) c: m 38 8 Aug. C 19 16 .07 1 39 8 Aug. C 20 17 .08 4 67 1 A0 8 Aug. C 15 13 .05 AI 8 Aug. C 17 15 .08 3 A2 8 Aug. c 18 16 .06 A3 8 Aug. C 20 17 .09 I 78 AA 8 Aug. C 22 18 .12 18 2 45 8 Aug. C 20 17 .07 17 3 1 A6 8 Aug. C 18 I6 .07 1A 5 2 A7 8 Aug. C 17 15 .06 A 48 8 Aug. C 17 15 .05 - 49 15 Aug. S 17 14 .05 1 50 15 Aug. 5 17 15 .06 51 15 Aug. 5 19 16 .06 4 52 22 Aug. 5 17 15 .05 I 53 22 Aug. S 19 16 .07 4 54 22 Aug. 5 20 17 .08 7 55 22 Aug. S 19 16 .07 3 1 2 56 22 Aug. 5 19 15 .06 3 3 57 22 Aug. 5 18 15 .05 A 58 22 Aug. S 20 17 .09 5 1 59 22 Aug. 5 15 13 .05 9 8 8 60 22 Aug. 5 19 16 .07 8 2 4 61 22 Aug. 5 18 16 .05 5 1 3 62 22 Aug. S 23 18 .12 1 21 6 63 22 Aug. 5 20 17 .07 7 6A 22 Aug. 5 20 16 .08 9 6 3 65 22 Aug. 5 22 20 .11 I 2 66 22 Aug. 5 19 16 .05 3 9 4 67 22 Aug. 5 20 16 .07 7 68 22 Aug. 5 19 I6 .07 8 69 22 Aug. 5 17 1A .0A 3 1 70 22 Aug. S 22 18 .10 1 11 15 15 71 22 Aug. 5 19 I6 .06 5 72 22 Aug. 5 19 16 .07 8 7 13 73 22 Aug. 5 22 18 .11 1A 8 74 22 Aug. S 23 19 .13 10 6 27 Table 12. (cont'd.) 28 . GUT CONTENTS .5: L m L 3}: Q) VCAA .. '2 m Icg E E '15 .- 13 2‘53 W‘Ovvv : 20.- d.“ “1‘0 0:. o o Q..._Q.QL 5%“.‘im-f-i§ 388*“8128 .5 <4 m.5 1— «n c m m e g m g .3. u o a 'o m m o L m E I: 8 3.2 8.5'28883u V) E u E .c u o -— a. —- :3 83.961.29.28 UQQ—lUUQm 75 22 Aug. N 32 26 .38 7 76 22 Aug. N 30 24 .28 2 77 22 Aug. N 37 30 .58 1 78 22 Aug. N 27 23 .23 A 79 22 Aug. C 22 18 .11 14 4 8 80 22 Aug. C 17 15 .06 2 81 22 Aug. C 22 18 .11 18 1 1 82 22 Aug. C 22 19 .10 8 1 83 22 Aug. C 21 18 .11 15 84 22 Aug. C 19 17 .07 6 1 2 85 22 Aug. C 22 19 .13 II 86 22 Aug. C 21 18 .09 5 1 1 87 22 Aug. C 18 16 .06 6 1 1 88 22 Aug. C 18 15 .06 7 1 2 89 22 Aug. c 21 17 .08 10 2 90 22 Aug. C 20 17 .08 91 22 Aug. C 20 18 .06 9 2 92 22 Aug. C 21 18 .08 15 1 4 93 22 Aug. c 30 25 .29 26 2 7 94 22 Aug. C 21 18 .09 9 1 95 22 Aug. C 19 17 .06 10 1 8 96 22 Aug. C 20 18 .07 10 3 97 22 Aug. C 22 18 .11 20 98 22 Aug. C 21 18 .10 16 1 99 22 Aug. C 20 18 .07 8 1 7 100 22 Aug. C 21 I8 .09 1 1 101 22 Aug. C 21 18 .10 6 102 22 Aug. C 17 15 .05 10 7 103 22 Aug. 0 I6 15 .0A 2 2 58 10A 22 Aug. c 19 16 .05 5 3 105 22 Aug. C 17 14 .04 16 4 106 22 Aug. c 20 18 .09 5 3 107 22 Aug. C 21 19 .10 6 108 22 Aug. C 17 15 .05 2 3 7 109 22 Aug. C 18 I6 .06 6 110 22 Aug. C 20 I8 .08 6 I 111 22 Aug. C 18 15 .05 10 3 29 Table 12. (cont'd.) . GUT CONTENTS {5:3 32 :3 VS" A1“ ’- .5 8 01 ”SEE :: 2.; 4.. 3 L m m'u ~a ~w a. 54 - -- a. . a, L C3“ 0: 0 :3 0.3.111 1110 Nu M Nu m - . u m a. a. 81 u C Qt.- .l 43 CWUICUUIUIWO. 83 "“514 0; “0101083ng '5 .28 8.5288886 3 3‘” 8552823813 9 .2 8851955138 112 22 Aug. c 21 18 .09 II {”3" 113 22 Aug. c 18 16 .06 12 IIA 22 Aug. C 2A 20 .16 I9 6 115 22 Aug. C 18 15 .06 4 116 22 Aug. C 18 15 .06 7 1 117 22 Aug. C 21 I9 .11 10 9 28 118 22 Aug. C 20 18 .06 8 119 22 Aug. C 15 13 .03 5 1 120 29 Aug. N 17 14 .05 2 2 121 29 Aug. N 19 16 .07 3 5 16 8 122 29 Aug. N 16 14 .05 6 3 123 29 Aug. N 16 14 .05 2 3 10 124 29 Aug. N 17 15 .06 2 1 125 29 Aug. S 20 17 .06 1 17 1 126 29 Aug. 5 21 I8 .10 127 29 Aug. S 22 19 .14 10 1 17 128 29 Aug. S 21 18 .10 14 9 46 129 29 Aug. 5 20 16 .08 10 1 130 29 Aug. 5 19 I6 .07 A 5 I6 131 29 Aug. S 20 16 .06 5 2 5 132 29 Aug. 5 21 18 .01 7 6 2A 133 29 Aug. 5 20 17 .09 24 2 6 13A 29 Aug. 5 I9 17 .07 8 135 29 Aug. 5 19 17 .05 1 11 2 136 29 Aug. S 18 15 .05 2 137 29 Aug. 5 19 17 .06 1 17 29 Aug. 5 19 I6 .06 1 I 29 Aug. S 18 15 .06 1 29 Aug. s 20 18 .09 1 I 5 3 29 Aug. 5 23 20 .12 29 2 17 29 Aug. 5 19 16 .06 17 2 29 Aug. 5 19 16 .07 10 2 24 29 Aug. 5 17 15 .05 I 2 29 Aug. 0 I8 16 .06 8 58 29 Aug. c 17 15 .05 8 2 29 Aug. C 19 17 .07 8 2 29 Aug. c 15 13 .0A 1 13 29 Aug. C 20 17 .09 7 2 Table 12. (cont'd.) 30 . GUT CONTENTS .2" t'E :21: 15 VSAAA :: -g 9 "J E E J? z: .3 . . 3 L 0 m'o ~# ~’ —- C O. 01 m c a u m c - a. . - -- a. - G. L e 99:113.; §3&&-“‘”&‘"3 9 :3 ”59¢; =9929999 -— o a '0 m m o L 31 E I: 8 1351 8. .E 'E .3 .2 o 3 Au a. a o E .c u o -— —- .. .2 888182"§1% c: an 1: .1 e: 8: c: m 150 29 Aug. C 19 I7 .07 2 3 25 151 29 Aug. c 25 21 .18 2 2 22 152 29 Aug. C 21 18 .12 15 2 13 153 29 Aug. c 18 16 .05 12 A 15A 29 Aug. c 18 16 .06 37 155 29 Aug. C 25 21 .19 27 9 65 156 29 Aug. C 18 16 .07 4 29 157 29 Aug. 0 I9 16 .07 A 1 3 158 29 Aug. C 18 16 .06 1 159 29 Aug. c 23 20 .13 12 31 160 29 Aug. C 18 16 .06 3 23 161 29 Aug. C 17 16 .06 5 1 3 162 29 Aug. C 19 16 .06 6 163 29 Aug. C 22 19 .11 5 55 164 29 Aug. C 23 20 .12 14 16 I65 29 Aug. C 16 1A .0A 1. 166 29 Aug. C 18 16 .05 1 1 167 29 Aug. C 22 17 .10 4 1 168 29 Aug. C 21 19 .09 6 37 I69 5 Sept. 5 15 13 .0A 2 170 5 Sept. 5 I8 15 .06 19 5 1 171 5 Sept. S 19 15 .06 10 172 5 Sept. 5 20 I6 .06 5 173 5 Sept. 5 I9 15 .06 10 2 3 17A 5 Sept. S 20 I6 .07 1 175 10 Sept. C 22 18 .10 1 14 10 30 176 19 Sept. S 22 20 .IA I I 20 A 177 19 Sept. 5 22 20 .14 , 1 4 22 8 178 19 Sept. S 23 20 .17 1 9 3 131 13 179 19 Sept. 5 23 20 .11 1 13 38 18 19 Sept. 5 21 I7 .10 6 9 71 A0 19 Sept. S 21 18 .17 1A 2 I 19 Sept. 5 2A 20 .17 55 3 63 39 19 Sept. S 23 20 .15 32 10 35 18 19 Sept. S 22 20 .13 9 12 20 5 19 Sept. S 22 18 .11 46 5 47 33 19 Sept. S 22 20 .19 1 9 31 Table 13. Capture, length, weight and gut content data for brook silversides. lg,‘ GUT CONTENTS ET: 2“ L V; A A o— .2 .13 E E 15 ._ t: g e m'o 7d 7’ 7’ 1: '2 d. él m = 3 8 85 .1 .1 .3 9 9 9 3 59 9 m 3 i 93 '55 '4 "4 3 3 3 1% e 9 3 5 ‘5 '5 ° .28 8 9 .9 8 3 9 9 '5 0) Q50 0. -- 1: O .0 o .1.» u .2- 9 9 S 9 ‘9 8 ".3 9 '5 V’ o o m o .c >. .- -u U m D _l U U Q 1U "T=="8 Aug. C ZA"”‘22""706 2 5 2 8 Aug. S 32 27 .15 1 3 8 Aug. S 35 30 .19 7 A 15 Aug. S A3 38 .33 8 2 5 15 Aug. S A2 35 .29 6 3 6 15 Aug. 5 30 26 .12 5 I 7 15 Aug. S 22 20 .0A 2 8 15 Aug. S 35 31 .19 25 2 9 22 Aug. 5 53 46 .58 2 7 2 10 22 Aug. S 46 40 .37 1 3 11 22 Aug. S 56 48 .78 3 2 2 12 22 Aug. S 50 AA .A6 3 A 13 22 Aug. S 25 22 .06 4 3 14 22 Aug. N 53 46_ .61 1 8 15 22 Aug. N 50 45 .48 7 16 22 Aug. N 50 45 .47 8 17 22 Aug. N 42 37 .32 1 0 18 29 Aug. c 63 53 1.01 23 3 2 19 29 Aug. C 58 31 .77 5 20 29 Aug. C 53 46 .60 1 6 2 21 29 Aug. C 40 36 .28 1 2 8 22 29 Aug. C A7 Al .A3 2 1 23 29 Aug. N 25 21 .06 2 1 2 24 29 Aug. N 53 45 .63 5 7 4 4 25 29 Aug. N 42 25 .28 39 4 5 2 26 29 Aug. N 41 3A .28 5 3 0 7 27 29 Aug. N 51 44 .57 17 1 5 4 28 29 Aug. N 63 53 .95 33 3 2 7 29 29 Aug. N 59 51 .75 81 5 4 3o 29 Aug. N 60 52 .88 12 3 1 31 29 Aug. N 44 38 .33 33 2 1 3 32 29 Aug. N 55 48 .71 20 4 5 33 29 Aug. S 25 21 .06 1 34 29 Aug. S 55 48 68 7 35 29 Aug. 5 37 31 .19 4 3 32 Table 13. (cont'd.) . GUT CONTENTS .2" 3'6 2: L V: A A .— 3 .3 E E ’3. ._ “.3 E v V v o— “o a o 3 cu m'o -— c o. 13.1 m c S 3 8% .3 .3 .3 9 .5. .5. '5. 9 Eu 9.1 3'5 c u m .- . . 3 m G. O. u g tCUL'U m5 1- m c 1n U1 3 13 111 13 .9. ._ u 0:: 1: m m o L m E D u -— o o c ._ 'u o a. o 0 am a. -- c O .o o u 4-: O- E :11 E .c u 0 — Q .— 9 3 '8' 8 819.2 91.2 .5 U m G —l U U Q m 37 29 Aug- 5 37 31 .20 5 ' 3 38 29 Aug. S 44 39 .35 13 6 39 29 Aug- 5 39 22 -33 17 40 29 Aug. S 27 24 .10 8 41 29 Aug. S 43 38 .31 4 2 42 29 Aug. S 56 48 .70 26 1 43 5 Sept. S 60 52 .89 2 1 9 44 5 Sept. S 32 27 .15 2 12 1 45 5 Sept. S 46 39 .36 3 46 5 Sept. S 38 31 .23 2 47 5 Sept. S 30 25 .09 8 4 48 5 Sept. S 39 34 .21 1 1 1 49 5 Sept. 5 39 34 .27 so 5 Sept. S A2 36 .36 48 51 5 Sept. S 41 26 .29 2 1 1 52 5 Sept. S 61 54 .94 3 53 5 Sept. S 22 20 .05 1 10 54 5 Sept. S 53 46 .69 9 55 5 Sept. S 37 31 .24 8 1 7 A 56 5 Sept. S 63 52 .93 1 57 5 Sept. 5 44 40 .34 8 1 2 3 58 5 Sept. S 28 21 .10 6 1 2 59 5 Sept. S 17 15 .02 3 2 60 5 Sept. S 28 25 .12 1 61 5 Sept. S 51 44 .56 5 62 5 Sept. S 52 45 .60 1 8 63 5 Sept. S 48 42 .53 1 5 64 5 Sept. S 32 28 .18 4 2 1 2 65 5 Sept. S 31 27 .16 2 4 2 66 5 Sept. S 37 33 .24 1 4 67 5 Sept. S 37 32 .24 4 1 1 68 5 Sept. 5 31 27 .15 1 50 1 69 5 Sept. 5 34 29 .21 2 70 5 Sept. S 38 34 .31 2 2 71 5 Sept. S 51 44 .62 4 1 19 72 5 Sept. S 26 21 .07 85 5 73 5 Sept. S 32 21 .18 1 1 1 2 Table 13. (cont'd.) 33 GUT CONTENTS 39" C's—u £1: L w: A A .- 8 .3 E E ’3. .- a: E v V v u. '0 o o 3 0.) (0'0 F- : 0-1 ON ‘0 c S 3 8 5 .J .J J 3' d. d. I; 31 d. 3‘ 8 C H ‘0 '- 1' ' 3 10 DA 0. Q1 ‘4 2 gr) 111.5 1- m c 1n 1n 1': 1; 1n 1; 9 '5 ° .28 8 ‘e" .‘2 8 8 8 8 ° 0 nun a. -- c o .o o u -H O. E Q) E .C H O '— 91 '- 9 .11 8- 8 8 8 2 ° .2 a U a: O .J U a Q 1'5 7A 5 Sept. S 31 27 .15 1 2 A2 2 2 75 5 Sept. 5 30 27 .13 4 20 2 76 5 Sept. S 25 21 .06 77 5 Sept. S 36 30 .19 78 5 Sept. S 31 27 .19 79 5 Sept. S 31 27 .16 7 8o 5 Sept. 5 38 32 .26 7 1 2 81 5 Sept. S 31 26 .13 2 179 7 1 82 5 Sept. S 37 31 .24 1 83 5 Sept. S 5A A7 .70 11 84 5 Sept. S 32 28 .28 4 85 5 Sept. S 25 23 .05 86 5 Sept. 5 27 23 .08 1 1 1 32 4 87 5 Sept. S 31 27 .16 2 2 2 88 5 Sept. S 28 32 .23 1 1 3 89 5 Sept. 5 2A 21 .06 A6 90 5 Sept. S 32 29 .12 20 1 1 93 91 5 Sept. S A2 37 .31 A 1A5 A 92 5 Sept. S 21 19 .04 2 1 10 3 93 5 Sept. S 26 22 .07 101 3 94 5 Sept. 5 46 40 .41 1 15 95 5 Sept. S 26 22 .06 1 17 96 5 Sept. S 19 16 .02 4 97 5 Sept. 5 22 20 .03 1 2 98 5 Sept. S 23 19 .06 5 9 99 5 Sept. 5 32 27 .11 2 14 4 3 100 5 Sept. S AA 39 .37 1 A 5 2 2 101 5 Sept. S 25 21 .05 6 2 1 2 2 102 5 Sept. S 25 21 .08 9 6 77 1 103 5 Sept. S 33 28 .16 2 8 104 5 Sept. S 44 39 .32 3 105 5 Sept. 5 54 47 .67 4 2 1 2 106 5 Sept. S 32 27 .14 3 1 2 107 5 Sept. S 26 23 .08 1 7 1 108 5 Sept. S 23 21 .05 1 1 109 5 Sept. 5 32 28 .14 1 11 2 4 110 5 Sept. S 31 26 .12 1 1 A 1 Table 13. (cont'd.) 34 GUT CONTENTS in 11"}; £33 L v: A A .- -§ "3 J; 13 35 :: 35 . . = 9 W . . . - . .5 31.9 2 C LO 0: O. 0.1 3 u {u m .4 .4 Au 3 13.1 01 .x m a. m 0 : um .— o o 3 to m D. 0'1 H 2 3“ 01.5 I" W C m m e g 1D 13 .3. .- c; o a '0 m m o L 31 E a: u -— o o c .- -u o o o OJD o. .- c o .n o u u a. E m E .c u o -— a. - w .2 8- 3 8 8.2 :2 s U m D _l U U a m 111 5 Sept. 5 25 22 .08 ' 10 2 1 112 5 Sept. S 39 33 .38 1 1 113 5 Sept. S 26 22 .06 1 10 6 114 5 Sept. S 32 29 .17 3 2 115 5 Sept. S A3 38 .35 A 116 5 Sept. S 28 25 .10 1 2 1 6 117 5 Sept. N 64 55 1.04 1 118 5 Sept. N 61 53 .91 2 1 119 5 Sept. N 63 55 .97 1 2 S 120 5 Sept. N 64 55 1.07 14 1 121 5 Sept. N 63 55 .95 4 122 5 Sept. 0 71 62 1.A5 8 123 5 Sept. C 74 66 1.70 9 124 5 Sept. C 74 64 1.69 2 20 125 5 Sept. 0 61 53 1.00 1 1 11 126 5 Sept. C 61 53 .93 4 127 5 Sept. 0 53 A7 .57 1 1 128 10 Sept. N 69 62 1.23 1 1 1 1 129 10 Sept. N 72 64 1.50 1 8 130 10 Sept. N 73 64 1.46 2 2 12 131 10 Sept. N 69 60 1.29 1 2 132 10 Sept. N 6A 56 .93 7 133 10 Sept. N 73 63 1.AA 23 134 10 Sept. N 70 60 1.17 135 10 Sept. N 72 63 1.AA 1 3 136 10 Sept. N 71 63 1.39 9 137 10 Sept. C 65 58 1.10 11 138 10 Sept. C 64 55 .97 5 139 10 Sept. C 59 52 .76 6 140 10 Sept. C 72 63 1.39 5 2 1 1A1 10 Sept. 0 65 56 1.0A 1 16 142 10 Sept. C 69 63 1.38 15 3 6 143 10 Sept. S 61 53 .84 4 1 144 10 Sept. 5 70 61 1.31 145 10 Sept. 5 41 63 1.47 46 3 1A6 10 Sept. 5 72 6A 1.A2 16 147 10 Sept. 5 67 58 1.15 2 9 35 Table 13. (cont'd.) . GUT CONTENTS £32: 8 2 L EEAA .- -§ "3 .5. 15 39 r: 33 . . a m m'u —- c a. o. m “‘58 35.1.389333201333 Egg-g ELI-.cgz‘cugmemmg‘a 83 :28 82.288883 8 8‘" 882882;: 9 8 888822.28 QED—IUUDM 1A8 10 Sept. 5 73 6A 1.A9 1A5 2 1 1A9 10 Sept. 5 AA 38 .31 1 150 10 Sept. 5 63 55 .95 2 151 19 Sept. N 52 44 .54 1 152 19 Sept. N 63 54 .93 1 153 19 Sept. N 67 59 1.12 1 1 154 19 Sept. N 69 60 1.20 9 2 2 155 19 Sept. N 72 63 1.A6 156 19 Sept. N 52 45 .51 11 2 2 72 157 19 Sept. C 73 63 1.44 2 158 19 Sept. C 66 58 1.11 2 159 19 Sept. C 60 52 .83 11 160 19 Sept. 5 53 A6 .61 3 2 7 161 19 Sept. S 48 42 .44 22 1 2 5 1 162 19 Sept. S A2 36 .26 18 163 19 Sept. 5 42 36 .26 4 6 34 91 16A 19 Sept. 5 78 68 1.95 118 5 9 LIST OF REFERENCES LIST OF REFERENCES Baumann, P. C. and J. Kitchell. 1974. Diel patterns of distribution and feeding of bluegill sunfish (Lepomis machrochirus) in Lake Wingra, Wisconsin. Trans. Amer. Fish. Soc. 103(2):255-260. Emlen, J. 1966. The role of time and energy in food preference. 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