Selection of Small Daphnia pulex by Yellow Perch Fry in Oneida Lake, New York

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Abstract
Length distributions of Daphnia pulex in yellow perch (Perca flavescens) fry stomachs and in simultaneously collected plankton samples were compared for evidence of size‐selective predation in Oneida Lake, New York. On 15 of 18 sample dates during a 6‐week period in midsummer, yellow perch fry selectively fed on D. pulex that were significantly smaller than those in plankton samples. No evidence of fluctuation in size selection as a result of diurnal vertical migrations of D. pulex or movements of yellow perch fry was found. A relationship between yellow perch length and D. pulex length was demonstrated: yellow perch consistently selected smaller D. pulex than they were capable of consuming from the population. We hypothesize that size selection by yellow perch results from interactions among learned predatory search images; greater escape potential of large, faster‐swimming D. pulex; and low attack proficiency of young, weak‐swimming yellow perch fry.