Turbidity-induced changes in emergent effectsof multiple predators with different foragingstrategiesMatthew M. VanLandeghem, Michael P. Carey*, David H. WahlKaskaskia Biological Station, Illinois Natural History Survey, Sullivan, IL, USA

Accepted for publication January 26, 2011

Abstract – In natural systems, prey frequently interact with multiple predators and the outcome often cannot bepredicted by summing the effects of individual predator species. Multiple predator interactions can create emergenteffects for prey, but how those change across environmental gradients is poorly understood. Turbidity is anenvironmental factor in aquatic systems that may influence multiple predator effects on prey. Interactions between acruising predator (largemouth bassMicropterus salmoides) and an ambush predator (muskellunge Esox masquinongy)and their combination foraging on a shared prey (bluegill Lepomis macrochirus) were examined across a turbiditygradient. Turbidity modified multiple predator effects on prey. In clear water, combined predators consumed in totalmore prey than expected from individual predator treatments, suggesting risk enhancement for prey. In moderatelyturbid water, the predators consumed fewer prey together than expected, suggesting a risk reduction for prey. At highturbidity, there were no apparent emergent effects; however, the cruising predator consumed more prey than theambush predator, suggesting an advantage for this predator. Understanding multiple predator traits across a gradient ofturbidity increases our understanding of how complex natural systems function.

Key words: clay turbidity; multiple predators; risk enhancement; risk reduction; muskellunge (Esox masquinongy); largemouth bass(Micropterus salmoides)

Introduction

Predator–prey interactions are central to understand-ing food web dynamics (Brooks & Dodson 1965;Schmitz 2007). Previous studies have most oftenfocused on the interaction between single predatorand prey species, whereas recent studies havehighlighted the importance of evaluating multiplepredators simultaneously to reflect natural systems(Sih et al. 1998; Eklov & VanKooten 2001; Griffen2006). Studies of multiple predator interactions haverapidly proliferated, but our ability to predict theoutcome of these interactions may be dependent onsystem-specific conditions. Thus, exploring multiplepredator–prey interactions across environmental

gradients is a critical next step (Scharf et al. 2006;Schmitz 2007).

The combined effects of multiple predators may notalways be predicted by summing the pairwise inter-actions of single predators (Siddon & Witman 2004;Griffen 2006). Nonadditive effects arise when preda-tors influence the foraging of another predator and ⁄orinfluence the behaviour of shared prey. Foragingstrategies of individual predators determine whetherthe nonadditive effects are positive or negative forcapture success and growth rates of each species(Schmitz 2007). From the perspective of the prey,multiple predators may prompt outcomes unpredictedfrom when prey are exposed to individual predators(Matsuda et al. 1993; Sih et al. 1998; Eklov & Werner

Correspondence: M. M. VanLandeghem, Texas Cooperative Fish and Wildlife Research Unit, Texas Tech University, Agricultural Sciences Room 218, 15th andBoston, Lubbock, TX 79409-2120, USA. E-mail: matt.vanlandeghem@ttu.edu

*Present address: NOAA Northwest Fisheries Science Center, 2725 Montlake Blvd. E., Seattle, WA 98112, USA.

Ecology of Freshwater Fish 2011: 20: 279–286Printed in Malaysia Æ All rights reserved

� 2011 John Wiley & Sons A/S

ECOLOGY OFFRESHWATER FISH

doi: 10.1111/j.1600-0633.2011.00494.x 279

2000; Eklov & VanKooten 2001). These emergenteffects on the prey can be risk enhancing or riskreducing depending on how foraging strategies of thepredators interact and the ability of prey to compensate(Sih et al. 1998; Schmitz 2007). Risk enhancementoccurs when an anti-predatory response to one pred-ator leads to a higher risk of predation from anotherpredator (Charnov et al. 1976; Soluk 1993). Preyspecies can experience a risk reduction in multiplepredator systems if predator species interfere with eachother or if prey response to one predator reduces therisk to another predator species (Crowder et al. 1997;Vance-Chalcraft & Soluk 2005; Griswold & Lounibos2006). For example, risk reduction often occurs whenprey respond to multiple predators simultaneously byreducing overall activity levels (Soluk 1993; Krupa &Sih 1998; Vance-Chalcraft et al. 2004; Vance-Chal-craft & Soluk 2005).

Multiple predator effects in aquatic systems may bestrongly influenced by environmental conditions aspredator–prey interactions change across environmen-tal gradients. For example, the interaction between twoaquatic predators was nonadditive at low densities ofvegetation but was additive at high densities (Swisheret al. 1998). Similarly, the capture success of com-bined predators was negatively related to increasingstructural complexity of macrophytes (Warfe & Bar-muta 2004). Habitat context and food resources alsoinfluence multiple predator food webs in rockysubtidal systems (Siddon & Witman 2004). Becauseabiotic factors differ in their effect on predation, otherfactors, such as turbidity, need to be considered tounderstand multiple predator interactions and effectsin natural systems (Scharf et al. 2006; Schmitz 2007).

Turbidity can alter predator–prey interactions byinfluencing the detection ability of predators and prey(Vinyard & O’Brien 1976; Gregory & Northcote1993; Van de Meutter et al. 2005; Shoup & Wahl2009; Carter et al. 2010). For instance, turbidity hasbeen found to affect anti-predatory behaviour of preyby reducing the reaction distance of prey to predators(Miner & Stein 1996; Abrahams & Kattenfeld 1997).Under turbid conditions, predators may alter theirforaging strategy by increasing strikes at any potentialprey (Crowl 1989). Under turbid conditions, the visualacuity of predators varies among species; thus,changes in turbidity could influence multiple predatorinteractions and effects. Understanding how multiplepredator interactions are influenced by turbidity willprovide insight into how aquatic communities react tochanging environmental conditions.

Turbidity is a common environmental condition inaquatic systems and can arise from both organic andinorganic sources. Nutrient loading (i.e., eutrophica-tion) can promote algal blooms (Lind 1986), whereasthe presence and abundance of macrophytes as well as

human development (e.g., urbanisation) within awatershed can influence the load of suspended solids(Moss 1977; Nixon 1995). Turbidity can also behighly variable within and across systems (Radke &Gaupisch 2005; Quesensberry et al. 2007) increasingrapidly, for example because of sediment run-offfollowing rainstorms (Chow-Fraser 1999). Further-more, turbidity is predicted to increase in somesystems with climate change, likely as a result ofincreased extreme precipitation events, erosion andrun-off (Nelson et al. 2009). We chose to focus oninorganic (clay) turbidity as it commonly occurs inmany aquatic systems and because organic turbiditymay have additional indirect effects on the aquaticenvironment, such as increased dissolved oxygenconcentrations during algal blooms (Koray 2004).

To test multiple predator effects across a gradient ofturbidity, we evaluated the interaction of two pisci-vores foraging on a shared prey at three levels ofturbidity. Predators included muskellunge (Esoxmasquinongy), an ambush predator (Webb & Skadsen1980; Rand & Lauder 1981; New et al. 2001), andlargemouth bass (Micropterus salmoides), a cruisingpredator (Savino & Stein 1989). The prey species wasbluegill (Lepomis macrochirus), which is a commonprey item for both predators, and all three species arenaturally sympatric. Previous work with these cruisingand ambush predators has found positive interactionsbecause of facilitation between foraging modes thatcreates a risk-enhanced effect on bluegill survival(Carey & Wahl 2010). When combined, the ambushpredator captured more prey than the cruising predatorin mesocosms with clear water (Carey & Wahl Inreview), whereas the cruising predator benefited inponds with more turbid water (Carey & Wahl 2010).This may possibly explain the discrepancy in resultsbetween these two studies. A direct relationshipbetween response of multiple predators and turbidity,however, has not been experimentally evaluated. Wetherefore tested the hypothesis that increasing turbiditywill decrease the risk-enhanced effects for prey becauseof alteration of predator interactions. In addition, weexamined the relative contribution of ambush andcruising predators to prey mortality in the combinedtreatments across three levels of turbidity to determinehow foraging mode and turbidity might interact.

Materials and methods

Study organisms

The effects of multiple predators on a shared preyacross a gradient of turbidity were tested in meso-cosms at the Kaskaskia Biological Station (KBS),Illinois Natural History Survey, Sullivan, Illinois, from11 August to 10 October 2006. Bluegill [35–60 mm

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total length (TL)] and largemouth bass [mean ± stan-dard error (SE): 170 ± 74 mm TL] were both collectedfrom local lakes with similar physiochemical charac-teristics and similar fish communities common to thearea. Muskellunge (mean ± SE: 206 ± 49 mm TL)were obtained from the Jake Wolf Fish Hatchery inTopeka, Illinois, where they were raised on fatheadminnows. All predators and prey items were held inclear water prior to use in experiments. To assuresimilar experience among predators, largemouth bassand muskellunge were fed bluegill for 2 weeks andonly individuals that had captured, handled, andconsumed these prey were used in the experiment.Bluegill were collected from lakes that contained bothspecies. Optimal prey sizes were used and matchedbetween predators by adjusting predator TL. Optimalbluegill length is 25–32% of largemouth TL (Hoyle &Keast 1987) and 20–25% of muskellunge TL (Gillenet al. 1981). Prey size was kept within these narrowranges of high capture efficiency to test the effects ofturbidity and not prey size on total consumption.

Experimental design

Effects of multiple predators were examined with asubstitution design (Jolliffe 2000; Griffen 2006). Thepredator treatment consisted of cruising predator only(two largemouth bass), ambush predator only (twomuskellunge) and combined predators (one large-mouth bass and one muskellunge). The substitutiondesign was used to avoid confounding density-depen-dent effects and allowed us to compare the strength ofcombined ambush and cruising predators againstindividual conspecific interactions (Sih et al. 1998;Griffen 2006). Each predator treatment was evaluatedat three turbidity levels (three predator treat-ments · three turbidity treatments = nine total treat-ments) and each replicated seven times using newpredators and prey (six replicates for the combinedpredator treatment at 10 nephelometric turbidity units(NTU) because of a mortality of one of the predators).Turbidity levels examined were 0 NTU (mean ± SE:0.70 ± 0.16 NTU; secchi depth >51 cm), 10 NTU(mean ± SE: 11.52 ± 0.43 NTU; secchi depth �48 cm) and 40 NTU (mean ± SE: 38.17 ± 1.27; sec-chi depth � 30 cm). These levels were chosen torepresent low to relatively high turbidity conditionsobserved in natural systems. Turbidity was created byadding bentonite clay to each tank, and the particleswere continuously re-suspended using submersiblepumps (Radke & Gaupisch 2005). Turbidity wasestablished and maintained within 10% of the speci-fied NTU during each trial with a turbidimeter (Model2020; LaMotte Company, Chestertown, MD, USA),calibrated using a 10.00 NTU AMCO standard (LaM-otte Company). All trials were conducted in a

uniformly shaded outdoor area at KBS between08:00 and 16:00. Water temperatures averaged20.7 ± 0.3 �C across all trials.

Trials were run in nine round tanks (2.2 m diameter)filled to a depth of 51 cm with filtered water (1.9 m3

total volume). Within the tank, vegetated and open-water habitats were created by positioning two patchesof simulated vegetation on opposite sides of the tank(four patches total), whereas the remainder of the tankwas left open. Vegetated patches were made of stemscreated from green polypropylene rope measuring45 cm long and 5 mm in diameter and occupied0.324 m3 volume (17% of total tank volume). Stemswere secured to weighted plexiglass at a density of390 stemsÆm)2 and each vegetation patch covered a30 · 60 cm area of the tank bottom.

Predators were placed into the tank 24 h prior to thestart of the experiment to allow them to acclimate totank conditions and to standardise hunger levels. Fivebluegill were placed in translucent plastic boxes withmesh-covered openings within the tank and allowed toacclimate for 1 h. Bluegill density (1.3Æm)2) waswithin the range of natural communities (Hackney1979; Johnson et al. 1988). Releasing the prey andremoving the plastic boxes from the tank initiated theexperiments. Predators were allowed to forage for 8 hand then were removed. The tanks were drained andremaining prey items were counted and recorded. Inthe combined predator treatments only, we determinedthe contribution of each predator species to overallconsumption by gastric lavage (Kamler & Pope 2001).

Data analysis

The influence of turbidity on prey consumption in theambush predator-only and cruising predator-onlytreatments was evaluated using a one-way analysisof variance (anova). To determine whether turbidityhas an effect on multiple predator interactions, wecompared expected versus observed number of preyeaten for combined predator treatments across turbid-ity levels. Expected predator consumption was calcu-lated for the combined predator treatment based on theindividual predator treatments at each level of turbid-ity. The expected multiple predator effects (E) werecalculated as E = (OA · OC)

0.5, where OA is theobserved prey response in the presence of two ambushpredators and OC is in the presence of two cruisingpredators (Griffen 2006). We tested for the effects ofpredators (expected vs. observed) and turbidity (0, 10,and 40 NTU) on number of prey eaten using a two-way anova. A significant interaction term wouldindicate that multiple predator effects are influencedby turbidity. Following a significant interaction term,we used planned linear contrasts to compare theexpected and observed values at each level of turbidity

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(Griffen 2006). If the predators cause a risk-enhancedemergent effect for prey at a given turbidity level, thenthe observed value will be significantly higher than theexpected value. Conversely, a risk-reduced emergenteffect for prey at a given turbidity would be supportedif the observed value is significantly less than theexpected value.

To evaluate how the interaction between the cruisingand ambush predators in combined treatments changedacross turbidity levels, we compared the proportion oftotal prey eaten by each predator at each of the threelevels of turbidity. In the combined treatment, dietswere collected on the cruising and ambush predators.Diets were only included in the analysis if stomachcontents could be positively identified (n = 4, 0 NTU;n = 5, 10 NTU; n = 7, 40 NTU replications in whichstomach contents were positively identified). We testedfor the effects of predator foraging mode (ambush vs.cruising) and turbidity (0, 10 and 40 NTU) on theproportion of prey each predator consumed using atwo-way anova. Data were arcsine-square-root-trans-formed to satisfy the homogeneity of variance assump-tion of anova. We expressed predator consumption asa proportion of total prey eaten during each trial toaccount for the decreasing number of total preyconsumed with increasing turbidity levels. A signifi-cant interaction between predator foraging mode andturbidity would indicate that interactions betweenpredators are affected by changes in turbidity. Follow-ing a significant interaction term, a post hoc Tukey–Kramer HSD test was used to compare the proportionof total prey consumed by each predator at each level ofturbidity.

Results

In the ambush predator-only treatments, mean preyconsumption did not significantly differ across turbid-ities (F2,18 = 0.48, P = 0.62; 1.2 bluegill at 0 NTU,1.7 bluegill at 10 NTU and 1.3 bluegill at 40 NTU).Similarly, in the cruising predator-only treatments,prey consumption did not significantly differ amongturbidity levels (F2,18 = 0.32, P = 0.73; 1.9 bluegill at0 NTU, 2.6 bluegill at 10 NTU and 1.9 bluegill at40 NTU).

For combined predators, a significant interactionwas found for prey consumption between expected ⁄observed and turbidity levels (Table 1), indicatingthat the effects of multiple predators changed acrossturbidity levels. At the 0 NTU turbidity level, theobserved number of prey consumed was higher thanexpected based on the individual predator species(F1,35 = 5.67, P = 0.023; Fig. 1). The higher totalconsumption in the combined predator treatmentsuggests a synergistic interaction between the pred-ator species and an emergent effect that is risk

enhanced for the bluegill prey. Increasing the turbid-ity level to 10 NTU, the number of prey consumed inthe combined predator treatment was lower thanexpected (F1,35 = 4.24, P = 0.047; Fig. 1), indicatinga risk reduction for prey. Observed and expectedconsumption were not different at 40 NTU(F1,35 = 0.24, P = 0.63; Fig. 1), indicating neutraleffects from multiple predators at the highest turbiditylevel.

Diet data from the predators indicated turbidity hada marginally significant effect on the proportion ofprey consumed by each predator (Table 2). Ambushand cruising predators consumed similar proportionsof prey in clear water (0 NTU: Tukey–Kramer HSDtest, P = 0.95; Fig. 2) and moderately turbid condi-tions (10 NTU: Tukey–Kramer HSD test, P = 1.0;Fig. 2). At the highest turbidity examined (40 NTU),

Table 1. A two-way ANOVA on the number of prey eaten with main effects ofpredator treatments and turbidity. Predator treatments are the expected andthe observed for cruising and ambush predators combined. The expectedmultiple predator effects (E) were calculated as E = (OA · OC)0.5, where OA isthe observed prey response in the presence of two ambush predators and OC

is in the presence of two cruising predator (Griffen 2006). The expectedmultiple predator effects were calculated at each turbidity level (0, 10 and40 NTU) using the above equation.

Source of variation SS d.f. F P

Turbidity 2.75 2 1.48 0.24Predators 0.02 1 0.02 0.89Turbidity · predators 9.44 2 5.07 0.01

Error 32.58 35

NTU, nephelometric turbidity units.

Turbidity (NTU)0 10 40

Num

ber o

f blu

egill

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5ExpectedObserved* *

Fig. 1. Means (±1 SE) of expected and observed prey eaten bycruising and ambush predators across turbidity levels of 0, 10 and40 NTU. At each level of turbidity, the expected multiple predatoreffects (E) were calculated as E = (OA · OC)

0.5, where OA is theobserved prey response in the presence of two ambush predatorsand OC is in the presence of two cruising predator (Griffen 2006).An asterisk indicates a significant difference between expected andobserved consumption (linear contrast, P < 0.05).

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the cruising predator consumed a significantly higherproportion of prey than the ambush predator (Tukey–Kramer HSD test, P = 0.04; Fig. 2).

Discussion

Turbidity influenced multiple predator interactions andthe effect on the prey. Higher observed than predictedconsumption of prey in clear water (0 NTU) with bothpredators combined suggests there is a risk-enhancedsituation for prey (Sih et al. 1998). The results in clearwater agree with previous studies in similar meso-cosms with these two predators (Carey & Wahl Inreview). Risk enhancement is because of positiveinteractions between the predators as their differentforaging strategies increase predator–prey encountersand create a conflict for the anti-predator defences ofthe prey (Carey & Wahl In review). In addition to astrong manoeuvring defence, bluegills switch fromopenwater to vegetated habitats when confronted by acruising predator (Savino & Stein 1982; Howick &O’Brien 1983; Moody et al. 1983). A conflict arisesbecause by reducing the risk of predation from a

cruising predator, the risk of predation from anambush predator increases (Savino & Stein 1989).As predicted, we found that when combined, theambush predator on average captured a higherproportion of prey than the cruising predator, but thisdifference was not statistically significant.

An increase in turbidity changed the effect ofmultiple predators on the prey. Cruising and ambushpredators combined consumed fewer prey thanexpected, suggesting a risk reduction for prey atmoderate turbidity levels (10 NTU). Risk reductioncould be caused by predator interference (Sih et al.1998) or changes in prey behaviour (Miner & Stein1996). Largemouth bass, the cruising predator, hasbeen found to be very active between 10 NTU and19 NTU (Miner & Stein 1996). Predator interferencemay occur if the elevated activity of the cruisingpredator at high turbidity increases the frequency ofinteractions with the ambush predator and disrupts itsforaging activity. Risk reduction may also result fromalterations to prey behaviour such as a decrease in thereaction distance to predators that has been previouslyobserved for bluegill in turbid water (Miner & Stein1996). A decrease in reaction distance of prey maylower the encounter frequency with predators; lessactivity by the prey could reduce the predation risk toambush predators that are reliant on prey movementfor foraging.

At high turbidity (40 NTU), expected and observedconsumption in the combined predator treatmentswere not different, indicating risk for prey wasunchanged between single predator species and com-bined predator species treatments. As turbidityincreases, direct interactions between predators andprey have been found to become increasingly impor-tant as the influence of indirect effects is reduced (Vande Meutter et al. 2005). At low and moderate turbid-ities, indirect effects between predators and prey canstill occur. The emergent effects of risk enhancementin clear water or risk reduction in moderately turbidwater, however, did not occur at high turbidity butinstead the consumption of prey was dependent uponthe individual foraging success of the predator species.The lack of emergent effects suggests that preymortality may be dependent on direct predator–preyinteractions at high turbidities.

Supporting the importance of direct predator–preyeffects at high turbidities, the cruising predatorconsumed a significantly higher proportion of preythan the ambush predator in the combined treatmentsat 40 NTU. High turbidity has been shown to uniquelyaffect the individual foraging abilities of largemouthbass and muskellunge. Largemouth bass are able totolerate turbidities as high as 70 NTU without largedecreases in capture success relative to clear water(Reid et al. 1999), whereas a significant reduction in

0 10 40

Pro

porti

on o

f blu

egill

0.0

0.2

0.4

0.6

0.8

1.0Cruising predatorAmbush predator *

Turbidity (NTU)

Fig. 2. Mean proportion (±1 SE) of prey consumed by cruisingand ambush predators in the combined predator treatment atturbidities of 0, 10 and 40 NTU. An asterisk indicates a significantdifference between predators (Tukey–Kramer HSD, P < 0.05).

Table 2. A two-way ANOVA on the proportion of prey consumed by eachpredator (cruising and ambush) within the combined predator treatments ateach level of turbidity (0, 10 and 40 NTU). The proportion of prey consumedwas arcsine-square-root-transformed to satisfy assumptions of homogeneityof variance.

Source of variation SS d.f. F P

Turbidity 0.00 2 0.00 1.00Predators 0.26 1 0.69 0.41Turbidity · predators 2.21 2 2.90 0.07

Error 9.90 26

NTU, nephelometric turbidity units.

Influence of turbidity on multiple predator effects

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muskellunge growth occurs between �30 NTU and�65 NTU in ponds with similar prey resources(Weithman & Anderson 1977). Although blindedmuskellunge are able to capture prey because of ahighly developed lateral line sense, they predomi-nantly rely on visual acquisition of prey (New et al.2001). Limited vision combined with low activitywhen foraging likely results in the low proportion ofprey consumed by the ambush predator at highturbidity. Furthermore, predator–prey encounter ratesof northern pike (Esox lucius), an ambush predatorclosely related to muskellunge, were shown to beinversely related to turbidity (Salonen & Engstrom-Ost2010), suggesting they may struggle to forage athigher turbidities. Turbidity effects on prey may alsoinfluence other predator–prey interactions. At highturbidities, bluegills reduce their anti-predatory behav-iour (Abrahams & Kattenfeld 1997) and use open-water habitat more than structured habitat (Miner &Stein 1996), potentially decreasing contact withambush predators such as muskellunge.

We were not able to evaluate the behaviour of thepredators or prey at different turbidities because oflimitations on visibility. Future studies quantifyingbehaviour, especially behavioural differences betweenpredator species, will provide further insights into themechanisms by which multiple predator effects changeacross turbidities. Also, because all prey species do notexhibit similar anti-predator behaviour or reactions toturbidity changes, an important next step would be toexamine prey species with different anti-predatorbehaviour and sensitivity to turbidity. These preymay have different responses to multiple predators andenvironmental conditions.

Predator composition is an important determinantof food web structure, and evaluating direct andindirect effects of multiple predators has increasedour understanding of complex animal communities(Sih et al. 1998; Eklov & VanKooten 2001; Schmitz& Sokol-Hessner 2002; DeWitt & Langerhans 2003;Siddon & Witman 2004; Griffen 2006; Schmitz2007). Determining the mechanisms by whichdifferent multiple predator effects occur involvesunderstanding both the characteristics of the indi-vidual predator species and prey species (Schmitz2007). Multiple predator effects on prey may beespecially dynamic in natural systems as preydensity and species composition vary across pro-ductivity and turbidity gradients (Jeppesen et al.2000). Facilitation between predators may be weakerat high prey density than at low prey density as thefrequency of prey encounters for one predator maynot be substantially increased by the behaviour ofthe prey responding to the other predator (Soluk1993). High prey densities in turbid, natural systemsmay therefore only create weak emergent effects on

the prey. Our study confirms the need for under-standing both predator foraging mode and anti-predator defences of prey in fishes but alsohighlights the importance of environmental condi-tions in predicting patterns in natural systems(Scharf et al. 2006; Schmitz 2007). Changes inturbidity because of natural and anthropogeniccauses could therefore not only affect the physio-chemical environment of natural systems but alsohave direct and indirect effects on aquatic commu-nities. A better understanding of these biotic andabiotic interactions will be crucial in improvingmanagement decisions for a variety of taxa acrossdifferent and changing environments.

Acknowledgements

We thank D. Shoup and M. Carter for their advice onexperimental design. M. J. Diana and the staff of the KaskaskiaBiological Station assisted in collecting largemouth bass andbluegill. We also thank S. Krueger and staff of the JakeWolf FishHatchery, Topeka, Illinois, for providing muskellunge. Financialsupport was provided by theUndergraduate Research Program ofthe College of Agriculture, Consumer, and EnvironmentalScience at the University of Illinois at Urbana-Champaign. Allprocedures conformed to the University of Illinois InstitutionalAnimal Care and Use Committee and comply with the currentlaws of the United States.

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