Zooplankton Production and Planktivore Consumption in Lake Pend Oreille, Idaho

This paper assesses the feeding demand of planktivores in Lake Pend Oreille in relation to crustacean zooplankton food availability. The copepods Diacylops bicuspidatus thomasi and Diaptomus ashlandi accounted for 75% of the standing zooplankton biomass over a two-year study period, whereas Daphnia spp. were the cladocerans of highest biomass. Annual zooplankton production, estimated using temperature-dependent empirical models that relate production to biomass, was 97.11 and 139.19 kg·ha−1. During the same study years, we estimate that zooplankton consumption by the lake's two primary planktivores, kokanee Oncorhynchus nerka, and the opossum shrimp Mysis relicta, comprised 56 and 42% of total zooplankton production. Consumption of cladoceran zooplankton, the preferred prey for both planktivores, was estimated to be 63% of production over the study period. Although few studies exist that relate zooplankton production to consumption by the planktivore community, data suggest high levels of zooplankton consumption in relation to production in Lake Pend Oreille, and that insufficient zooplankton abundance may exist to support management efforts to increase kokanee abundance.