Effects of Prey Size, Abundance, and Population Structure on Piscivory by Yellow Perch

Abstract

To examine how predator and prey body sizes, prey abundance, and prey population structure affect piscivore–prey interactions, feeding experiments were conducted on large (> 190 mm total length, TL) and small (150–189 mm) yellow perch Perca favescens given small (43–55 mm TL), medium (60–66 mm), and large (71–80 mm) fathead minnows Pimephales promelas as prey. Handling costs suggested that large yellow perch should not discriminate among prey sizes, but small yellow perch should select small fathead minnows over large, Results of feeding trials with only one size of prey were consistent with the cost indications. Large yellow perch consumed similar numbers and biomasses of the three size-classes of fathead minnows in trials with only one size of prey available, Small yellow perch ate more small fathead minnows than medium and more medium than large, Thus, small yellow perch gained less weight with large fathead minnows than with small ones as their prey. When all three prey sizes were available, both large and small yellow perch consistently captured more small fathead minnows than large, even when total prey abundance or the size structure of prey populations varied. Overall consumption by large yellow perch was not affected by prey abundance, but small yellow perch increased consumption at higher abundances by eating more small and medium prey. Increasing the proportion of medium fathead minnows, while decreasing the proportion of large prey, did not affect total consumption by either large or small yellow perch. However, small yellow perch responded to this shift by eating more medium and fewer large fathead minnows. Selection by yellow perch for prey fish smaller than expected based on gape limitations and handling times, and the responses of yellow perch to changes in their prey base under experimental conditions, help explain patterns of predation and coexistence between this piscivore and its prey in nature.