A simulation model of PCB dynamics in the Lake Ontario pelagic food web

Salmonid stocking and reduced phosphorous loading have led to major changes in the Lake Ontario ecosystem over the last 25 years and during the last 15–20 years PCB concentrations in age 4+ lake trout have dropped from ca. 9 to 3 mg kg−1. Here, I present a simulation model that examines PCB dynamics by coupling a dynamic prey supply to a multi-species functional response model of predation. At 1994 target levels of stocking, the model predicts that chinook salmon will increase, but alewife, lake trout and steelhead will decrease in biomass over the next 10 years. PCB concentrations of the sport fish are predicted to be 1.28, 1.77 and 3.06 mg kg−1 for steelhead, chinook salmon and lake trout, respectively. If alewife growth rates are not reduced farther, the model predicts that alewife could recover from a severe winter mortality. Decreases in the growth rates of sport fishes were accompanied by higher PCB concentrations and lake trout always had higher PCB concentrations for a given age class than chinook salmon and steelhead. Therefore if minimal sport fish PCB concentrations are a principal goal, managers should stock less lake trout, and stock more of the faster growing and less contaminated chinook salmon and steelhead.