Kokanee Foraging: ADaphniain the StomachIs Worth Two in the Lake

Abstract

Abstract We estimated percent dry matter per unit biomass of ambient Daphnia spp. and of Daphnia spp. (both predominately D. pulex) from stomachs of kokanee Oncorhynchus nerka to test the hypothesis that kokanee can reduce the water content of their prey. Percent dry matter of consumed Daphnia did not differ from that of ambient Daphnia in May–June, but was approximately double that of ambient Daphnia in July and August. We also found that percent dry matter of zooplankton in kokanee stomachs did not increase with decreasing gut fullness. Consequently, water reduction probably occurred during ingestion and enabled kokanee to pack a larger number of prey into their stomachs. The results suggest that kokanee may be able to capture twice as many Daphnia per unit time than previously predicted. Additionally, consumption estimates from a bioenergetics model that used wet-mass energy density of prey derived from field samples resulted in P-values (proportion of maximum consumption) greater than 1.0, whereas wet...