PISCIVORES, PREDATION, AND PCBsIN LAKE ONTARIO’S PELAGIC FOOD WEB

Abstract

PCB concentrations in Great Lakes sport fishes continue to concern managers. Proposed reductions in consumption advisories, if adopted, would increase pressure to further reduce contaminant concentrations. However, management of Great Lakes pelagic food webs for minimum PCB concentrations and maximum sustainability represents a potential conflict. Here I use a detailed age-structured chinook salmon–alewife model to examine the potential for changes in stocking rates to further reduce contaminant concentrations in Lake Ontario’s chinook salmon. Uncertainty surrounding recruitment of alewife, the principal prey of all stocked salmonids, is considered, and sustainability of alewife is cast in probabilistic terms. The interaction between size-selective predation and chinook salmon growth rates leads to a relatively narrow range of chinook salmon stocking that should keep the alewife eaten small (thus having relatively low PCB concentrations) but not reduce the age structure of the alewife population to few reproductive individuals. Stocking rates necessary to achieve PCB consumption advisories ≤0.5 mg/kg fish mass carry ≈90% probability of an alewife population crash. Modest increases (25%) in current stocking rates would decrease PCB concentrations of chinook salmon without a large increase in the probability that the alewife population would crash. These results are applicable to other salmonids (coho salmon and lake, rainbow, and brown trout), because they too exhibit size selective predation, and their recruitment is largely determined by stocking.