FEEDING ECOLOGY OF LARVAL FISHES IN LAKE ROOSEVELT, WASHINGTON

Food habits, feeding selectivity, and diet overlap were analyzed for l arval walleye (Stizostedion vitreum), yellow perch (Perca flavescens), sculpins (Cottus spp.), and suckers (Catostomus spp.) collected in La ke Roosevelt, Washington, in May to July 1982. Larval diet of fishes i n this unique co-occurring species mix has not been previously describ ed. Larval fishes 4-25 mm long were sampled weekly with 0.5-m townets from nearshore sites at two stations. Zooplankton was collected with M iller samplers to characterize food availability. The most abundant fo od items were calanoid copepods in walleye stomachs, calanoid and cycl opoid copepods in yellow perch stomachs, and cyclopoid copepods in scl upin stomachs. Larval walleyes 9 to 24 mm long also preyed upon larval fishes. Cladocerans were important food only to larval suckers, which fed almost exclusively on Bosmina and Chydorus. Feeding selectivity, determined by Wilcoxon's nonparametric signed-rank analysis, showed po sitive selection for several prey items among the fish taxa. Schoener' s niche overlap values indicated significant diet overlap between wall eye and yellow perch. During our study period, effects of competition on growth, survival, and character divergence of larval walleye and ye llow perch was minor. Annual variation in reservoir conditions could r esults in stronger or weaker competitive interactions than we observed since zooplankton composition is known to influence fry feeding succe ss and growth.