Supplementl Feeding of Bluegill s Smll Impoundment Enhncement for Lrgemouth Bss by Stephen Russell Woodrd A thesis submitted to the Grdute Fculty of Auburn University in prtil fulfillment of the requirements of the Degree of Mster of Science Auburn, Albm My 9, 2011 Keywords: pond mngement, bluegill, supplementl feeding, lrgemouth bss, recretionl fishing Copyright 2011 by Stephen Russell Woodrd Approved by Dennis R. DeVries, Co-chir, Professor of Fisheries nd Allied Aqucultures Russell A. Wright, Co-chir, Associte Professor of Fisheries nd Allied Aqucultures Aln Wilson, Assistnt Professor of Fisheries nd Allied Aqucultures
Abstrct Severl pond enhncements re commonly used to increse fish production or enhnce ngling opportunities. I investigted whether providing supplementl feed to bluegill leds to higher reproductive rtes, nd if the indirect effects of bluegill feeding improve lrgemouth bss growth. During 2009 nd 2010, dult bluegill nd lrgemouth bss were stocked into nine 0.1-h ponds; ponds were provided with no pelleted food (control), low rtion (1.52-kg h -1 d -1 ), or high rtion (2.68-kg h -1 d -1 ). Supplementl feeding incresed growth of initilly-stocked bluegill, femle bluegill gond weight, lrvl bluegill density, nd ge-0 lrgemouth bss growth incresed compred to the control. Adult lrgemouth bss size nd fll ge-0 bluegill density nd biomss did not increse with feeding. Supplementl pellet feeding is clerly beneficil when the pond mngement gol is to increse bluegill size nd reproductive output, nd this improved condition of the bluegill popultion resulted in enhnced growth of ge-0 lrgemouth bss. ii
Acknowledgments I would first like to thnk my co-dvisors Drs. Dennis DeVries nd Russell Wright for their guidnce nd support throughout my studies t Auburn University. Mny thnks lso to Dr. Aln Wilson who provided support nd insightful comments s prt of my dvisory committee. I would like to extend specil thnks to Tmmy DeVries for ll of her tedious clorimetry nd zooplnkton work. I m extremely thnkful for the mny technicins nd grdute students who helped with this project in the field nd lbortory: Tommy Purcell, Brndon Simcox, Crig Roberts, Emily DeVries, Mdeline Wedge, nd Zchry DeVries. I would lso like to thnk Dvid Glover for his guidnce with sttisticl nlyses. I m grteful for Drs. Jim Stoeckel nd Allen Dvis for the use of their equipment. I pprecite the funding tht helped support this work tht cme from dontion from Willim Irelnd, nd the generous dontion of feeders to this project from Moultrie Feeders. Lstly, I would like to thnk my wife Lindsy for her love, support, nd encourgement throughout my grdute reserch ssistntship. iii
Tble of Contents Abstrct... ii Acknowledgements... iii List of Tbles... vi List of Figures... vii Introduction... 1 Methods... 6 Pond Setup... 6 Supplementl Feeding... 7 Abiotic Mesures nd Plnkton Smpling...7 Fish Smpling... 8 Clorimetry... 10 Anlyses... 10 Results... 13 Abiotic Mesures nd Plnkton... 13 Adult Bluegill...13 Lrvl nd Age-0 Bluegill... 15 Adult nd Age-0 Lrgemouth Bss... 17 Discussion... 19 Bluegill... 19 iv
Lrgemouth Bss... 22 Mngement Implictions... 23 Literture Cited... 25 v
List of Tbles 1. Fertiliztion dtes for ponds in the 2009 & 2010 field sesons... 31 2. Summry of mesures for 2009 & 2010 field sesons... 32 3. Model results for seprte mixed-model repeted mesures nlysis of vrince (RMANOVA) run for ech biotic nd plnkton mesure... 33 4. Adult fish percent survivl (±1 SE) for the 2009 nd 2010 field sesons... 34 vi
List of Figures 1. Men dily temperture ( C) in experimentl ponds. Feeding tretments re unfed control (solid line), low feeding (dotted line), nd high feeding (dshed line)... 35 2. Men (± SE) dissolved oxygen concentrtion (mg/l) in experimentl ponds. Feeding tretments re unfed control (circles, solid line), low feeding (tringle, dotted line), nd high feeding (squre, dshed line)... 36 3. Men (± SE) secchi depth (cm) in experimentl ponds. Symbols re s in Figure 2... 37 4. Men (± SE) turbidity (NTU) in experimentl ponds. Symbols re s in Figure 2... 38 5. Men (± SE) chlorophyll concentrtion (µg/l) in experimentl ponds. Symbols re s in Figure 2... 39 6. Men (± SE) zooplnkton density (No./m 3 ) in experimentl ponds. Symbols re s in Figure 2... 40 7. Men (± SE) weight (g) of dult bluegill in experimentl ponds (mixed-model RMANOVA). Symbols re s in Figure 2... 41 8. Men (± SE) totl length (mm) of dult bluegill in experimentl ponds (mixed-model RMANOVA). Symbols re s in Figure 2... 42 9. Men (± SE) reltive weight (Wr) of dult bluegill in experimentl ponds (mixedmodel RMANOVA). Symbols re s in Figure 2...43 10. Men (± SE) cloric density (cl/g wwt) of dult bluegill in the fll (mixedmodel ANOVA) for the three feeding tretments in the 2009 nd 2010 field sesons. Brs with the sme letters indicte tretment mens did not differ significntly...44 11. Men (± SE) gond weight (g) nd gondosomtic index (%) of dult bluegill in experimentl ponds (mixed-model ANOVA) for the 2010 field seson. Filled brs re for femles, open brs re for mles. Brs with the sme letters indicte tretment mens did not differ significntly within sexes. Error brs were clculted using lest-squred mens...45 vii
12. Men (± SE) densities (No./m 3 ) of lrvl bluegill in experimentl ponds from July to September (mixed-model RMANOVA) for the 2009 field seson. Symbols re s in Figure 2...46 13. Men (± SE) densities (No./m 3 ) of lrvl bluegill in experimentl ponds from April to August (mixed-model RMANOVA) for the 2010 field seson. Symbols re s in Figure 2...47 14. Men (± SE) growth (mm/dy) of lrvl bluegill in experimentl ponds from April to August (mixed-model RMANOVA) for the 2010 field seson. Symbols re s in Figure 2...48 15. Men (± SE) length (mm) to the 15 th dily ring for fll-collected bluegill (mixedmodel ANOVA) for the three feeding tretments in the 2009 field seson. Brs with the sme letters indicte tretment mens did not differ significntly..49 16. Men (± SE) number nd biomss (g) of ge-0 bluegill in the fll (mixed-model ANOVA) for the three feeding tretments in the 2009 field seson. Brs with the sme letters indicte tretment mens did not differ significntly...50 17. Men (± SE) number nd biomss (g) of ge-0 bluegill in the fll (mixed-model ANOVA) for the three feeding tretments in the 2010 field seson. Brs with the sme letters indicte tretment mens tht did not differ significntly...51 18. Cloric density (cl/g wwt) of fll ge-0 bluegill t hrvest (mixed-model ANCOVA) for the 2009 field seson. Symbols re s in Figure 2...52 19. Cloric density (cl/g wwt) of fll ge-0 bluegill t hrvest (mixed-model ANOVA) for the 2010 field seson. Symbols re s in Figure 2...53 20. Men (± SE) weight (g) nd totl length (mm) of dult lrgemouth bss in experimentl ponds (mixed-model RMANOVA) for the 2010 field seson. Symbols re s in Figure 2...54 21. Men (± SE) reltive weight (Wr) of dult lrgemouth bss in experimentl ponds (mixed-model RMANOVA). Symbols re s in Figure 2...55 22. Men (± SE) cloric density (cl/g wwt) of dult lrgemouth bss in the fll (mixed-model ANOVA) for the three feeding tretments in the 2010 field seson. Brs with the sme letters indicte tretment mens did not differ significntly...56 23. Men (± SE) weight (g) nd totl length (mm) of ge-0 lrgemouth bss in experimentl ponds (mixed-model RMANOVA) for the 2009 field seson. Symbols re s in Figure 2...57 viii
24. Men (± SE) weight (g) nd totl length (mm) of ge-0 lrgemouth bss in the fll (mixed-model ANOVA) for the three feeding tretments in the 2010 field seson. Brs with the sme letters indicte tretment mens did not differ significntly. Error brs were clculted using lest-squred mens...58 25. Length-frequency histogrm of ge-0 lrgemouth bss in the fll for the 2010 field seson. Feeding tretments re unfed control (filled blck brs), low feeding (filled light-gry brs), nd high feeding (filled drk-gry brs)...59 26. Men (± SE) number nd biomss (g) of ge-0 lrgemouth bss in the fll (mixedmodel ANOVA) for the three feeding tretments in the 2010 field seson. Brs with the sme letters indicte tretment mens did not differ significntly. Error brs were clculted using lest-squred mens...60 ix
Introduction Smll impoundments or ponds re generlly reservoirs less thn 40-h surfce re (Duwlter nd Jckson 2005). These mn-mde wter fetures re bundnt cross the United Sttes with n estimted 2.6 million locted on privte lnd (Smith et l. 2002). Although used for vriety of purposes, such s irrigtion, swimming, or livestock wter, smll impoundments re most often used for recretionl fishing (Duwlter nd Jckson 2005; Hley 2009). Fishing in these ponds initilly requires fish stocking, but the number nd species of fishes to stock in smll impoundments continues to be questioned (Modde 1980; Duwlter nd Jckson 2005). While other species re sometimes stocked, lrgemouth bss, Micropterus slmoides, nd bluegill, Lepomis mcrochirus, re most commonly stocked (Swingle nd Smith 1941; Swingle 1946; Modde 1980; Duwlter nd Jckson 2005). Swingle (1946) concluded tht lrgemouth bss nd bluegill could generte blnced predtor-prey interction. Swingle nd Smith (1941) found bluegill to be sustinble prey choice for lrgemouth bss, becuse they hve diverse diet, tolerte wide rnge of tempertures, nd they reproduce multiple times in seson (Gross 1982). Bluegill re protrcted spwners (Grvey et l. 2002; Lovshin nd Mtthews 2003), nd spwning occurs in distinct synchronous bouts with severl colonies forming nd spwning t one period, which is followed by period of inctivity before the next mjor spwning event (Crgnelli nd Gross 1996). The number of these spwning bouts per yer vries depending on vriety of intercting fctors including ltitude, temperture, wether, food vilbility, nd other biotic nd biotic fctors (Jolley et l. 2009). 1
Some of the gols of smll impoundment owners re to produce hrvestble size bluegill nd lrgemouth bss, mximize fish ctch, nd mintin sustinble long-term fish hrvest in their ponds. Mintining blnced predtor-prey system tht ccomplishes these gols cn be chllenge, leding to the development of wide vriety of enhncement techniques tht cn be used to elevte fish production in the pond (Hley 2009). These enhncements include stocking supplementl forge species such s thredfin shd Dorosom petenense (Noble 1981), instlling fish ttrctors, nd using supplementl pellet feed (Schmittou 1969; Lewis nd Heidinger 1971; Berger 1982; Porth et l. 2003). While these enhncements re commonly used in prctice, they hve not lwys been scientificlly evluted. Supplementl feeding with prepred pelleted feeds is used by pond owners to increse fish productivity, becuse fish growth often is limited by food vilbility (Schmittou 1969; Lewis nd Heidinger 1971; Murnyk et l. 1984; Porth et l. 2003). Fish feeders re instlled round the pond to provide supplementl food for fish nd to improve the condition of stunted fish popultions limited by food resources (Berger 1982; Murnyk et l. 1984). Another dded benefit to supplementl feeding is tht it ttrcts prey fish from other prts of the pond to the feeding res (Berger 1982). The ddition of pellet feed is trgeted towrds prey fish, bluegill, to improve growth nd body condition. The prey fish re lso sometimes pellet fed with the gol of improving lrgemouth bss growth nd condition. In theory prey species tht re supplementlly fed should grow to lrger sizes nd hve greter energy reserves nd therefore should produce more young (i.e. prey for lrgemouth bss). However, this link between supplementl feed nd greter prey resources for lrgemouth bss hs not been evluted. 2
The quntity of supplementl feed to be distributed on dily bsis required to produce the best growth in bluegill is unknown nd likely vries cross ponds. It would be beneficil to identify such rte to reduce loss vi excess feed while mximizing feeding effects. Feeding t high rtes cn lso result in lgl blooms. Current recommendtions suggest feeding bluegill no more thn wht they will et in 10 to 15 minutes, or not more thn 11 kg/h per dy (Wright nd Msser 2004). In other studies bluegill were fed bsed on their estimted body weight: Schmittou (1969) fed bluegill t rte of 3% of totl fish weight per dy nd stted tht more thn 11 kg/h of feed ws not used. Twibell et l. (2003) fed bluegill t food llotment equivlent to 4% of the fish body weight ech dy. Yet, feeding bluegill bsed on body weight is imprcticl in smll impoundments becuse fish re continuously growing, nd modifiction of the mount of pellet feed would need to be djusted frequently in proportion to the biomss of bluegill in the pond. Supplementl feeding cn be expensive for pond owners nd it is importnt to know if it is biologiclly beneficil to bluegill reproduction nd lrgemouth bss condition nd growth. Severl studies hve exmined the effects of pellet feeding of bluegill with feeds of differing protein levels, mesuring the resulting fish growth in quri (Tidwell et l. 1992; Hoglnd et l. 2003; Twibell et l. 2003). Higher protein pellet feeds contining 37 to 44% crude protein re more beneficil to bluegill weight gin thn lower protein feeds (Tidwell et l. 1992; Hoglnd et l. 2003). However, the cost of feed cn be prohibitive, becuse protein in the pellet feed represents mjor cost in the formtion of feed (Hoglnd et l. 2003). Determining the protein percentge in pellet feed tht is most cost effective depends on the purpose of feeding. Aquculture fcilities rising 3
bluegill t high densities (>10,000/h) my be ble to fford higher protein feed (38-44% crude protein), which is often formulted s feed for slmonids or other gmefish species. Yet, privte pond owners who wnt only to provide supplementl feed for bluegill stocked t verge densities (2,500/h) cn use lower protein diets (28-36% crude protein) tht re less expensive but still provide sufficient clories nd protein to enhnce fish growth. It is lso suggested by nutritionist s tht bluegill get sufficient protein from nturl foods nd the pellets lrgely give them clories which spres the nturl protein (R. A. Wright, personl communiction). Although feeding bluegill cn increse their size nd condition (Schmittou 1969; Berger 1982; Hoglnd et l. 2003; Twibell et l. 2003), it is unknown wht effects supplementl feeding hs on their reproductive rtes. Ady et l. (2006) compred bluegill somtic nd gond tissue growth in unfertilized nd fertilized ponds. Mture femle bluegill in unfertilized ponds hd lower bsolute gond weights thn mture femles in fertilized ponds, suggesting preferentil lloction of energy to somtic tissue when food is scrce (Ady et l. 2006). Therefore, the mount of resources vilble my influence bluegill totl reproductive output, which my directly increse lrgemouth bss food supply. Supplementl fed bluegill my produce more eggs, or they my spwn more often in seson thn unfed bluegill, but to dte there is no evidence for this. Here I exmine whether supplementl feeding of bluegill in smll impoundments enhnces lrgemouth bss growth nd condition. More specificlly, I m sking the following questions: 4
1) Does feeding bluegill led to higher bluegill reproductive rtes, s mesured by lrvl fish density during the spwning seson, fll ge-0 density, nd gond weight? 2) Do lrgemouth bss size nd reltive weight improve in ponds where bluegills re provided supplementl feed? 5
Methods Pond Setup I conducted two seprte whole-pond experiments t the E.W. Shell Fisheries Center, South Auburn Unit, Auburn University, Auburn, Albm, one in 2009 nd one in 2010. Nine 0.1-h ponds (2-m deep t one end, nd <0.5-m deep in the opposite end) were drined nd treted with lime CCO 3 (12,000 kg/h) in Mrch 2009 to increse lklinity, which increses the effectiveness of fertilizer (Wright nd Msser 2004). New filters (300-µm mesh size) were dded to the experimentl pond inflow pipes to prevent fish lrve from entering the ponds s they were filled from n djcent reservoir pond. After filling, ll ponds were fertilized with 9.4 L/h of10-34-0 (N-P-K) liquid fertilizer to stimulte phytoplnkton bloom (Wright nd Msser 2004). Becuse it is stndrd pond mngement prctice for mintining phytoplnkton bloom, dditionl fertilizer ws dded periodiclly during the experiment (Tble 1) to ttempt to mintin uniform secchi depth of 80-cm in ll ponds nd prevent excessive pond weed growth. When pond weeds (Potomogeton spp.) strted to grow in the ponds in My of 2010, herbicide (Rewrd ctive ingredient: diqut dibromide) ws pplied once to ll ponds with sinker (Pro-Mte Sinker) t rte of 9.4 L/h. Dissolved oxygen levels were monitored closely for the next 72 hours, nd when the dissolved oxygen dropped to less thn 4.0 mg/l, wter ws flowed through ll ponds to circulte nd erte the wter. All ded weeds were rked out of the ponds fter the herbicide tretment. All ponds were stocked with bluegill nd lrgemouth bss, the typicl community stocked cross the United Sttes. Bluegill fingerlings (40-70 mm TL) re normlly stocked into ponds t density of 2,500/h (Modde 1980; Wright nd Msser 2004; 6
Duwlter nd Jckson 2005). Becuse there re no recommendtions for stocking intermedite size reproductively mture bluegills (75-120 mm TL) we stocked them t hlf the recommended fingerling rte (1,250/h) in 2009. In 2010, dult bluegill (75-120 mm TL) were stocked t the recommended fingerling rte (2,500/h). Due to unnticipted problems in finding 210-260 mm TL dult lrgemouth bss in 2009, ge-0 lrgemouth bss (120-170 mm TL) were stocked insted of dults in erly August t rte of 150/h. Adult lrgemouth bss were stocked t rte of 250/h (210-260 mm TL) in April 2010 immeditely following bluegill spwn. Supplementl Feeding Pellet feeding occurred from June to September in 2009 nd April to August in 2010. There were three experimentl tretments, ech replicted in three seprte ponds: two feeding tretments nd control. Ponds were provided with no pelleted food (control), low rtion (1.52 kg h -1 d -1 ), or high rtion (2.68 kg h -1 d -1 ). The three tretments were rndomly ssigned to the nine ponds, with three ponds per tretment. Automtic fish feeders (Moultrie Directionl Fish Feeder; 23 L cpcity) were instlled beside ech tretment pond, nd timers were clibrted to disperse defined mount of food once dily t 0800 hours, when feeding ctivity is typiclly high. I used commercil floting ctfish food (F-R-M Ctfish Fingerling Grower/ 36% crude protein; distributed by Flint River Mills in Binbridge, GA). Abiotic Mesures nd Plnkton Smpling Tempertures were mesured t depth of 1-m in the deep section of ech pond t two-hour intervls with wterproof Hobo temperture pendnt dt loggers (Model UA- 002-64). Dissolved oxygen (mg/l) ws mesured t 1-m depth from the deep end of 7
ech pond t 0900 hours every 72 hours (Yellow Springs Instrument Model 51 B). Wter smples were collected once every 14 dys for chlorophyll nd turbidity in 500-ml drk polyethylene bottles tht were plced directly on ice. Turbidity ws mesured with nephelometer (NTU; HF Scientific, Inc. Microw TPW) nd chlorophyll concentrtions were determined using fluorometer (µg/l; Turner Designs Aqufluor). Wter smples (500-ml) were filtered onto 47-mm dimeter glss fiber disc (Millipore ) nd chlorophyll ws extrcted in cold 95% ethnol for 24h, followed by fluorometric nlysis (Welschmeyer 1994). A summry of ll these mesures nd their smpling frequency is given in Tble 2. Zooplnkton were collected from ech pond once every 14 dys with verticl tow of zooplnkton net (30-cm dimeter; 50-µm mesh) from 1-m to the surfce t 0800-1000 hours. Smples were preserved in 90% ethnol for lter identifiction in the lbortory under dissecting microscope. In the lbortory, smples were enumerted until t lest 200 individuls of the most bundnt tx were counted or until the entire smple ws counted (Dettmers nd Stein 1992; Welker et l. 1994). Cldocerns were identified to genus, nd copepods were identified s cyclopoids, clnoids, hrpcticoids, or nuplii. Fish Smpling Limnetic lrvl fish were smpled once per week during the bluegill spwning seson from April to September with n ichthyoplnkton net (0.5-m dimeter; 500-µm mesh) fitted with flow meter to llow determintion of towing speed nd wter volume smpled for estimtion of lrvl fish density. The ichthyoplnkton net ws pulled the length of ech pond, with two replicte smples collected from ech pond on ech 8
smpling dte. Once every 30 dys we conducted 15-minute trnsect in ech pond using bot-mounted pulsed-dc electrofishing (Smith-Root Inc. DC electrofisher, 5.0 GPP, 1000 W) to collect rndom smples of dult lrgemouth bss nd bluegill. Collected fish were mesured (TL; nerest mm) nd weighed (wet weight; nerest g) nd returned to the pond. Ponds were drined nd ll fish were hrvested in September of 2009 nd August of 2010. Adult fish were collected, weighed (g), sexed, mesured (mm TL), nd frozen for lter nlysis. Age-0 bluegill were collected, ll individuls in rndom subsmple were counted (n= pproximtely 500), nd the entire smple ws weighed (nerest g). The number of fish nd weight of the subsmple ws then extrpolted to estimte the number of ge-0 bluegill in the pond. To determine if there were differences in growth rtes of ge-0 bluegill between experimentl feeding tretments, sggitl otoliths were removed from ge-0 bluegill in 2009 nd otolith dily rings were counted to estimte ge in dys (Tubert nd Coble 1977). A rndom subsmple of ge-0 bluegill ws mesured (nerest 0.01 mm TL) nd individuls were put into size clsses (n=5 per 10-mm size clss; typicl size rnge 15-85 mm TL). Then the otoliths of those fish were removed nd mounted on microscope slides using thermoplstic cement. Otoliths were ground on the sggitl plne (1,000-grit sndpper) nd polished. We counted dily rings under oil immersion with compound microscope (400X mgnifiction). We were interested in the first 15 dys of life for the ge-0 bluegill, nd we took mesurements from the core of the otoliths to the 15 th dily ring. Age-0 otoliths were not removed in 2010, insted (n=5) lrvl fish otoliths were removed from ech pond every week. These otoliths were mounted nd red using the 9
sme process bove. Ech otolith ws ged independently by two different reders, nd if estimtes were within 10% they were verged. If they were not within 10%, then they were recounted until 10% ws reched. Clorimetry Bomb clorimetry ws used to determine if there were differences in men energy density of dult nd ge-0 bluegill mong feeding tretments. Adult bluegill (n=10, >130 mm TL) from ech pond were dried t 70 C until constnt mss ws chieved for two consecutive dys (<0.01 g between dys), nd the finl dry mss recorded. Individul ge-0 bluegill were combined within 10-mm size clsses (typicl size rnge =15-85 mm TL) nd dried. Dried dult bluegill smples were blended to homogenous mixture using coffee grinder, nd dried ge-0 bluegill were blended with mortr nd pestle; smples were dried gin to constnt weight (<0.01 g between dys) to remove ny moisture ccumulted during the mixing process (Glover et. l 2010). Two 0.1 to 0.2-g pellets were then formed nd ignited in semimicro bomb clorimeter (Prr Instrument Co., Model 1425 nd Model 6725) to mesure bluegill cloric energy content (Glover et. l 2010). Multiple ge-0 bluegill in the smll size clss (15-25 mm TL) were required to crete lrge enough pellets (0.1-0.2 g). Adult lrgemouth bss cloric densities were determined using the techniques outlined by Glover et. l (2010). Men cloric densities of the ge-0 bluegill size clsses, dult bluegill, nd dult lrgemouth bss were compred mong feeding tretments. Anlyses All dt were nlyzed using the Sttisticl Anlysis System (SAS Institute Inc., Cry, North Crolin, USA). I used mixed-model nlysis of vrince (ANOVA), 10
where mens of the ponds (rndom fctor) were nested within the fixed feeding tretments (low, high, nd control; PROC MIXED; SAS Institute 2008). Normlity nd homogeneity of vrince were ssessed to ensure tht the ssumptions of ANOVA were met. When significnt tretment effects were detected, lest-squres mens ws used to exmine where differences existed. Using mixed-model ANOVA, we tested for differences in the length of ge-0 bluegill t 15 dys nd dult bluegill gond weight (g). Mixed-model ANOVA ws lso used to test for tretment differences in cloric density of dult lrgemouth bss, dult bluegill, nd ge-0 bluegill. An nlysis of covrince (ANCOVA) ws used to determine if significnt correltions existed for ge-0 bluegill body mss mong tretment type for cloric density fter determining tht interctions were insignificnt. Density nd biomss of ge-0 bluegill nd ge-0 lrgemouth bss t hrvest were compred mong tretments with mixed-model ANOVA. Men weight (g) nd men totl length (mm) of ge-0 lrgemouth bss were compred mong tretments with mixed-model ANOVA. Using mixed-model repeted-mesures nlysis of vrince (RMANOVA), we tested for differences in men lrvl fish density, lrvl fish growth (mm/dy), dult bluegill nd dult lrgemouth bss weight (g) nd totl length (mm) mong tretments. Temperture, secchi depth, dissolved oxygen, turbidity, chlorophyll, nd zooplnkton density were log-trnsformed to meet ssumptions of vrince nd then seprte RMANOVAs were run for ech vrible. A first-order utoregressive covrince structure ws used in ll of the RMANOVAs to ccount for correltions mong observtions within the fixed feeding tretments. 11
Percent survivl ws clculted s n f /n i, where n i ws the initil number of fish stocked into the pond, nd n f ws the number of fish recovered from the ponds (Sger nd Winkelmn 2006). Reltive weight (W r ) ws clculted to estimte condition for ech bluegill nd lrgemouth bss (Wege nd Anderson 1978). RMANOVA ws used to test for differences in lrgemouth bss nd dult bluegill reltive weight (W r ) mong tretments. The gondosomtic index (GSI) ws clculted to indicte the reproductive lloction in mle nd femle bluegill (Wootton 1990). GSIs were compred mong tretments nd sex with mixed-model ANOVA. 12
Results Abiotic Mesures nd Plnkton Temperture (Figure 1), dissolved oxygen (Figure 2), secchi depth (Figure 3), turbidity (Figure 4), nd chlorophyll (Figure 5) were not sttisticlly different mong tretments during either the 2009 or 2010 experiments (Tble 3). Zooplnkton density lso did not differ mong tretments during either 2009 or 2010 (Tble 3; Figure 6), nor were there ny differences in density of zooplnkton tx mong tretments in 2009 (mixed-model RMANOVA: F 24,234 = 0.47; P = 0.98) or 2010 (F 30,520 = 0.45; P = 0.99). The most bundnt txonomic groups were clnoid copepods, copepod nuplii, Diphnosom, nd Bosmin for both 2009 nd 2010. Adult Bluegill In 2009, dult bluegill verge weight (mixed-model RMANOVA: F 2,6 = 16.22; P = 0.0038); Figure 7) nd length (F 2,6 = 4.08; P = 0.076; Figure 8) in the high nd low feeding tretments ws significntly higher thn the control t the end of the experiment. There ws no difference between the high nd low feeding tretments. Men weight in the high nd low feeding tretments ws significntly higher thn the control in August nd September 2009, but not in June nd July (F 6,1516 = 48.55; P < 0.0001; Figure 7). Length in the high nd low feeding tretments ws significntly higher thn the control in September 2009, but not during June through August (F 6,1516 = 14.46; P < 0.0001; Figure 8). In 2010, dult bluegill weight (F 2,6 = 13.84; P = 0.0057; Figure 7b) nd length (F 2,6 = 9.04; P = 0.016; Figure 8b) were significntly higher in the high tretment thn the low tretment, which in turn ws significntly greter thn the control, t the end of the experiment. The high tretment, low tretment, nd control ponds ll differed from one 13
nother s bove during My through August, but during June the high tretment ws greter thn the low nd control, nd in Mrch nd April there were no differences between tretments in dult bluegill weight (F 12,3359 = 27.85; P < 0.0001; Figure 7b) or length (F 12,3359 = 15.56; P < 0.0001; Figure 8b). Adult bluegill reltive weight in the high nd low feeding tretments ws significntly higher thn the control t the end of the experiment in 2009 (mixed-model RMANOVA: F 2,6 = 10.52; P = 0.011; Figure 9), but the high nd low feeding tretments did not differ. The high nd low feeding tretments were significntly higher thn the control in August nd September, but not in June nd July (F 6,1516 = 16.18; P < 0.0001; Figure 9). In 2010, dult bluegill reltive weight in the low feeding tretment did not differ from tht in the high feeding tretment or control ponds (F 2,6 = 3.72; P = 0.089; Figure 9b), but ws significntly higher in the high feeding tretment versus the control. Reltive weight ws significntly higher in the high tretment thn the low tretment, nd the low tretment ws greter thn the control t the end of the experiment during July nd September (F 12,3359 = 14.65; P < 0.0001; Figure 9b). The high tretment differed from the control but not the low feeding tretment in June nd August. Adult bluegill whole-body cloric density in the high nd low feeding tretments t the end of the experiment ws significntly higher thn in the control in 2009 (mixedmodel ANOVA: F 2,6 = 11.96; P = 0.0081; Figure 10), with no difference between the high nd low feeding tretments. In 2010, dult bluegill whole-body cloric density in the high tretment t the end of the experiment ws significntly higher compred to the control (F 2,6 = 4.41; P = 0.066; Figure 10b), nd there ws no significnt difference between the high nd low feeding tretments. There were no significnt differences in 14
cloric density between mle nd femle bluegill in either 2009 (F 1,34 = 0.03; P = 0.87) or 2010 (F 1,80 = 0.89; P = 0.35). In 2010, the men dult bluegill gond weight in the high tretment, low tretment, nd control ponds ll differed significntly t the end of the experiment (mixed-model ANOVA: F 2,6 = 10.69; P = 0.011). Femle bluegill gond weight ws significntly higher in the high tretment compred to the low tretment nd the control (F 2,436 = 21.44; P < 0.0001; Figure 11). The gondosomtic index (GSI) of dult bluegill did not differ mong tretments in 2010 (F 2,6 = 2.38; P = 0.17). However, when sex ws specificlly exmined the femle bluegill GSI ws significntly higher in the high tretment compred to the low tretment nd the control (F 2,436 = 7.74; P = 0.0005; Figure 11b). There were no differences in dult mle gond weight nd GSI mong tretments. Lrvl nd Age-0 Bluegill There were no significnt differences in lrvl bluegill density mong tretments t the end of the experiment in 2009 (mixed-model RMANOVA: F 2,6 = 0.01; P = 0.99; Figure 12), but the low tretment differed from the high tretment nd control ponds the first two weeks in August (F 16,128 = 2.22; P = 0.0073; Figure 12). In 2010, lrvl bluegill density ws greter t the end of the experiment in the high feeding tretment compred to the low feeding tretment nd control (F 2,6 = 4.80; P = 0.057; Figure 13), nd the low feeding tretment nd the control did not differ. Lrvl bluegill density ws significntly higher in the high tretment thn the low tretment nd control ponds throughout July, nd the low tretment ws greter thn the control ponds throughout August, but the low nd high tretment did not differ in August (F 34,247 = 2.15; P = 0.0005; Figure 13). There 15
were no significnt differences for lrvl bluegill growth mong tretments bsed on otolith dily rings in 2010 (mixed-model RMANOVA: F 2,6 = 0.22; P = 0.81; Figure 14), lthough growth rtes did vry cross smpling dtes (F 14,519 = 5.73; P < 0.0001; Figure 14). Fish in the low feeding tretment grew fster thn in the high feeding tretment nd control throughout June (F 28,519 = 2.09; P = 0.001; Figure 14). There were lso no significnt differences for ge-0 bluegill bckclculted length t the 15 th dily ring mong tretments in 2009 (mixed-model ANOVA: F 2,6 = 2.38; P = 0.17; Figure 15), but trends suggest tht ge-0 bluegill in the high nd low feeding tretments grew fster thn in the control. The men number of fll ge-0 bluegill did not differ mong tretments in 2009 (mixed-model ANOVA: F 2,6 = 0.67; P = 0.55; Figure 16) or 2010 (F 2,6 = 0.52; P = 0.62; Figure 17), nd ge-0 bluegill biomss similrly did not differ mong tretments in 2009 (F 2,6 = 0.12; P = 0.88; Figure 16b) or 2010 (F 2,6 = 0.43; P = 0.67; Figure 17b). An nlysis of covrince for fll ge-0 bluegill whole-body cloric density reveled tht slopes did not differ mong tretments in 2009. After dropping the interction term between length nd tretment from the model becuse they were not significnt, wholebody cloric density did not differ mong tretments (mixed-model ANCOVA: F 2,6 = 0.98; P = 0.43; Figure 18). Similrly in 2010 ge-0 bluegill whole-body cloric density did not differ mong tretments (mixed-model ANOVA: F 2,6 = 3.72; P = 0.089; Figure 19). The slopes of the feeding tretments nd the control were significntly different from one nother due to the high nd low feeding tretments hving higher cloric density thn the control in the 100-120 mm size clss (F 2,102 = 8.80; P = 0.0003; Figure 19), but the high nd low tretments did not differ from ech other. 16
Adult nd Age-0 Lrgemouth Bss The weight of the initilly-stocked dult lrgemouth bss did not differ mong tretments throughout the experiment in 2010 (mixed-model RMANOVA: F 2,6 = 13.84; P = 0.56; Figure 20), nor did dult lrgemouth bss length (F 2,6 = 0.34; P = 0.72; Figure 20b). Reltive weight of dult lrgemouth bss in the two feeding tretments did not differ significntly from the control t the end of the experiment in 2010 (F 2,6 = 0.20; P = 0.83; Figure 21), nor did reltive weight differ mong tretments throughout the experiment (F 10,238 = 1.54; P = 0.13; Figure 21). Lrgemouth bss survivl ws low, but ws not ffected by tretment (mixed-model ANOVA: F 2,6 = 1.07; P = 0.40; Tble 4). In 2010, there were no differences mong tretments in dult lrgemouth bss whole-body cloric density (mixed-model ANOVA: F 2,6 = 0.41; P = 0.68; Figure 22). In 2009, stocked ge-0 lrgemouth bss weight in the high feeding tretment ws significntly lrger thn the low tretment nd control t the end of the experiment (F 2,6 = 6.75; P = 0.029; Figure 23), nd there ws no difference between the low tretment nd the control. Initilly-stocked ge-0 lrgemouth bss length ws lso greter in the high tretment compred to the low tretment nd control t the end of the experiment in 2009 (F 2,6 = 5.92; P = 0.038; Figure 23b). In 2010, ge-0 lrgemouth bss were the offspring of the dult lrgemouth bss. Men ge-0 lrgemouth bss weight t the end of the experiment did not differ mong tretments in 2010 (mixed-model ANOVA: F 2,6 = 1.75; P = 0.25; Figure 24), nor did men ge-0 lrgemouth bss length (F 2,6 = 1.34; P = 0.33; Figure 24b) lthough the trend of fish being hevier nd longer in the high feeding tretment ws similr to the 2009 results. However, length-frequency histogrm of 2010 ge-0 lrgemouth bss did show significnt difference in the length-frequency 17
distributions mong tretments t the end of the experiment (Kruskl-Wllis Test: χ 2 = 89.59 ; P < 0.0001; Figure 25), becuse the high tretment length-frequency distribution ws significntly greter thn the low tretment nd the control (Tukey s: t 469 = 3.33; P < 0.05). Age-0 lrgemouth bss number t hrvest did not differ mong tretments in 2010 (F 2,6 = 0.10; P = 0.91; Figure 26). There ws lso no difference mong tretments in 2010 in ge-0 lrgemouth bss totl biomss (F 2,6 = 1.52; P = 0.29; Figure 26b). 18
Discussion Incresed resource supply likely increses the totl reproductive output of prey species (Wootton 1973), which in turn my led to incresed prey vilbility to predtors t higher trophic levels. In mny wrmwter systems in North Americ, bluegill is common prey of the lrgemouth bss. Becuse fish growth is frequently limited by food vilbility (Hewett nd Krft 1993) nd fish fecundity is often directly relted to body size (Wootton 1979; Roff 1984), supplementl feeding is commonly used s pond enhncement technique to fuel this predtor-prey reltionship in controlled recretionl fishing ponds (Schmittou 1969; Lewis nd Heidinger 1971; Berger 1982; Porth et l. 2003), with the dded benefit of ttrcting prey fish from other prts of the pond to the feeding res (Berger 1982). Tht is, bluegill with n ugmented diet my produce more young either through producing more eggs t ech spwn or by spwning more often in seson thn unfed bluegill thereby providing more food for lrgemouth bss. The indirect effects of bluegill feeding medited through incresed production s prey, might improve lrgemouth bss growth nd condition, but to dte these effects hve not been evluted. In my whole-pond experiments conducted in two yers I found incresed bluegill gond weight nd lrvl bluegill density in feeding tretments compred to the control, nd tht this improved condition of the bluegill popultion resulted in enhnced growth of ge-0 lrgemouth bss. Bluegill As there is often direct correltion between fish size nd fecundity (Wootton 1979; Fletcher nd Wootton 1995), I expected incresed reproductive output in lrger, fed bluegill. Absolute gond weights were significntly higher for mture dult femle 19
bluegill in the high feeding tretment compred to the low feeding tretment nd control, presumbly becuse bluegill were ble to llocte more energy into reproduction. It is likely tht mture bluegill femles in the low feeding nd control ponds compensted for reduced cloric intke by investing greter proportion of clories into somtic versus gondl tissue growth (Lmbert nd Dutil 2000; Ady et l. 2006), or mintined their investment in somtic growth despite decresing energy intke. Different lloction strtegies in fish cn be indicted through the use of the gondosomtic index (GSI; Crim nd Glebe 1990), prticulrly for pproximting reproductive lloction in femles for fish with one restricted spwning period. However, for protrcted spwning species, such s pumpkinseed nd bluegill, reproductive lloction my not be effectively estimted with GSIs over the course of n entire spwning seson (Fox nd Crivelli 1998). Nevertheless, GSIs were significntly higher for mture dult femle bluegill in the high feeding tretment compred to the low feeding tretment nd control. Incresed dult bluegill gond weight should correspond with n increse in the number of eggs spwned (Wootton 1979; Roff 1984; Fletcher nd Wootton 1995), but complex set of intercting environmentl fctors contributes to egg nd lrvl fish mortlity (Dhlberg 1979). In the 2009 experiment, I did not see ny differences in the number of lrvl fish produced mong feeding tretments. However, during tht experiment bluegill were stocked lter in the spwning seson, nd it is possible tht bluegill did not hve dequte time to develop sufficient gond tissue from the pellet food to increse reproductive output mong feeding tretments. This hs been observed in crppie, where limited prey resources during the months preceding spwning cn ffect gond investment nd limit ovry production (Bunnell et l. 2007). However, crppie 20
spwn only once yer nd they rely on energy stores tht hve been cquired over long period of time to llocte to gond growth (i.e. cpitl spwners); bluegill re protrcted spwners nd must rely on recently cquired energy stores to donte to gond growth (i.e. income spwners; Bonnet et. l 1998, Bunnell et l. 2007). Interestingly, bluegill stocked erlier in the 2010 field seson yielded greter densities of lrvl fish in the feeding tretment ponds compred to the control. The longer study durtion nd erlier feeding dte in 2010 likely llowed bluegill to llocte more energy to gond growth. Supplementl feeding lso my hve hd less of n effect in 2009, becuse there ws more food per fish in the feeding tretments due to the lower bluegill stocking density in 2009 compred to 2010. However, by the fll of ech yer there were no differences in ge-0 bluegill numbers nd biomss mong tretments suggesting densitydependence ws operting in my experimentl ponds. In my experiments, growth of initilly-stocked bluegill incresed in response to supplementl feeding, consistent with severl other studies (Schmittou 1969; Lewis nd Heidinger 1971; Berger 1982; Porth et l. 2003). Fish growth nd biomss cn be higher in systems with high levels of productivity. Fertiliztion of ponds with phosphorous nd nitrogen is common prctice to stimulte plnktonic lge blooms nd thereby increse the productivity of the entire foodweb (Swingle nd Smith 1938). Supplementl feeding cn led to plnkton blooms similr to those stimulted by fertiliztion (Wright nd Msser 2004). In order to isolte the effect of feeding from plnktonic lge, ll the experimentl ponds were fertilized periodiclly to mintin constnt secchi depth. No biotic prmeters or plnkton densities differed significntly mong tretments in either yer, indicting tht fertiliztion helped control biotic fctors 21
nd plnkton, resulting in fish within ll ponds, regrdless of feeding tretment, experiencing similr environments throughout the smpling yer. Zooplnkton density nd zooplnkton txon-specific densities were lso similr mong ll ponds, nd bluegill used them s food resource in ddition to the supplementl feed. Thus, incresed growth of fed bluegill cn be ttributed to the supplementl feeding nd not vrition in biotic prmeters or plnkton densities. Becuse fertiliztion enhnced condition of bluegill in the control ponds reltive to wht would be seen in field situtions without fertiliztion, the effects of supplementl feeding through ll the trophic levels might hve been even more pronounced hd feeding tretments been compred to control bluegill popultion without fertiliztion. Lrgemouth Bss There were no differences in end-of-experiment dult lrgemouth bss weight, length, nd condition mong feeding tretments in 2010, despite n increse in dult bluegill reproductive output. There were trends in dult lrgemouth bss weight, but they were not significnt perhps due to lck of power. Additionl repliction or incresed study durtion my hve enhnced differences in weight for dult lrgemouth bss mong feeding tretments. In longer study more pronounced effects of bluegill reproduction could result from stored-lipid crryover from previous yers (McCormick nd Gglino 2008), which could result in detectble differences in lrgemouth bss growth nd condition mong feeding tretments tht consumes these bluegill. The ge-0 lrgemouth bss stocked in July in 2009 in the high feeding tretment did receive benefit from feeding. In 2010, ge-0 lrgemouth bss were not stocked, but the stocked dult lrgemouth bss were ble to spwn, nd the resulting ge-0 lrgemouth 22
bss popultion ttined lrger lengths nd weights in the high feeding tretment compred to the low feeding tretment nd the control. There ws no evidence of pellet food in the diets of rndomly-selected ge-0 lrgemouth bss from ech pond in either 2009 or 2010. Therefore, the ge-0 lrgemouth bss were not likely receiving direct benefit from the pelleted food, but rther n indirect resource enhncement from the incresed reproductive output of dult bluegill. Mngement Implictions Supplementl feeding is often employed s pond enhncement, but the link between supplementl feed for bluegill nd incresed prey resources for lrgemouth bss hs not been explicitly evluted. Feeding hs positive effects on bluegill growth nd condition (Schmittou 1969; Lewis nd Heidinger 1971; Tidwell et l. 1992; Hoglnd et l. 2003; Ady et l. 2006; Sger nd Winkelmn 2006). Additionlly, the gond weight of dult femle bluegill nd lrvl bluegill density incresed in feeding tretment ponds compred to control ponds. Adult lrgemouth bss growth nd condition were not enhnced, but ge-0 lrgemouth bss in feeding tretments chieved lrger sizes compred to those in the control. I expected to see incresed dult lrgemouth bss growth nd condition with corresponding increse in prey items tht were vilble to them, but this did not occur. Thus, there did not pper to be ny indirect effects of supplementl feeding on dult lrgemouth bss, but it did enhnce growth of ge-0 lrgemouth bss. The response of predtor popultions t high trophic levels often lgs behind chnges in prey popultions t lower trophic levels. For exmple, the lynx preys specificlly on snowshoe hres nd the popultion growth nd decline of the lynx lgs slightly behind the rise nd fll of the snowshoe hre popultion (Elton nd Nicholson 23
1942). Similrly, the dult lrgemouth bss my show lgged growth response behind the increse in bluegill reproductive output due to supplementl feeding. Thus, longerterm experiments must be used to determine whether supplementl feed provided to bluegill yields long-term indirect benefits for dult lrgemouth bss growth. Supplementl pellet feeding is clerly beneficil when the pond mngement gol is to directly increse bluegill size nd reproductive output, thereby enhncing the growth of ge-0 lrgemouth bss. 24
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