Feeding Ecology of Walleye, Stizostedion vitreum, Larvae: Effects of Body Size, Zooplankton Abundance, and Zooplankton Community Composition

We conducted laboratory experiments to examine the functional response and conducted comparative laboratory and field studies to examine the prey selection of walleye, Stizostedion vitreum, larvae. Maximum consumption rate (C max , micrograms per hour) increased exponentially with walleye mean length whereas the prey abundance at which 90% of C max is attained (D 90 , prey per litre) increased initially and then declined with mean length. Prey size had no significant effect on C max whereas D 90 declined significantly with increasing prey size. Selection for relatively larger prey and selection for large cladocerans relative to cyclopoid copepods increased significantly with walleye mean length. Walleye larvae consistently selected most strongly for relatively uncommon prey. Selection for relatively smaller prey and selection for cyclopoid copepods relative to large cladocerans increased significantly with total prey abundance in field studies and some laboratory studies. Variance in prey selection showed a significant, negative relationship with prey abundance in laboratory studies. Selection for medium (≥ 0.3–0.6 mm body width) relative to small (< 0.3 mm) prey declined significantly with increasing temperature in field studies. Our results suggest that the feeding success of walleye larvae may be limited by both the abundance and size composition of the zooplankton communities in natural environments.