Skaha Lake Kokanee 2005-10: Recruitment, Growth, Survival, and Competition with Mysis, Lake Whitefish and Stocked Age-0 Sockeye

Complex multi-species interactions among predators, prey and competitors in pelagic communities make prediction of introduced or invasive species impacts highly uncertain.  We used bioenergetics, production and consumption analysis to investigate the impacts of introducing sockeye salmon (Oncorhynchus nerka) into an existing pelagic food web comprising 7 species of zooplankton consumed by lake whitefish (Coregonus clupeaformis), kokanee (O. nerka) and mysids (Mysis relicta).  Mysids were the most important pelagic predators.  They invaded Skaha Lake in the 1970s, consumed 0.4% d^-1 of zooplankton biomass, caused periodic declines in Bosmina longirostris and Daphnia thorata, and were associated with the extirpation of 5 zooplankton species.  However, mysids also contributed 30-60% of the biomass consumed by older kokanee and whitefish.  The second most important predators were age 2-3 kokanee which consumed 0.1% d^-1 of zooplankton and 2% d^-1 of mysid standing-stocks.  Whitefish consumed 0.3% d^-1  of mysid standing-stocks.  Stocked age 0 sockeye consumed too little zooplankton (<0.01% d^-1 of standing stock) to serve as a serious food competitor of wild kokanee.