Zooplankton Community Changes at Pend Oreille Lake, Idaho: Testing Implications for Age-0 Kokanee Prey Selection, Digestion, and Growth

Abstract

Abstract We used laboratory and field experiments to investigate how spring and autumn zooplankton community changes at Pend Oreille Lake, Idaho, characterized by reduced cladoceran abundance, have affected the prey selection, growth, and digestion of age-0 kokanee Oncorhynchus nerka. In prey selection trials using newly emerged kokanee alevins (mean total length (TL) = 25 mm) with varied levels of stomach fullness and that were fed different ratios of cladocerans to copepods, cladocerans were selected except when their relative abundance was the lowest. Alevins ate more zooplankton when cladocerans were relatively more abundant and when their stomachs were empty, but stomach fullness did not influence the prey type selected. Alevins ingested prey that were larger than available prey at each level of stomach fullness, the greatest size selectivity occurring on empty stomachs. Underyearling kokanee (48–57 mm TL) that were fed cladoceran zooplankton ingested more biomass in 1 h than did those fed copepod zo...