WHY ARE THE PCB CONCENTRATIONS OF SALMONINE INDIVIDUALS FROM THE SAMELAKE SO HIGHLY VARIABLE

An individual-based model (IBM) was applied to the Lake Michigan rainb ow trout (Oncorhynchus mykiss) population, with the objectives of expl aining the observed variation in growth and in polychlorinated bipheny l (PCB) concentration within the population. When variation in prey PC B concentration was incorporated into the model, variability in PCB co ncentration among individual rainbow trout was fully explained by the IBM. Although number of spawnings and number of years spent in a strea m prior to first entering the lake were factors in determining growth, these life history characteristics appeared to have only a minor impa ct on PCB accumulation rate in rainbow trout. The IBM application to t he rainbow trout population was compared with an application to the La ke Michigan lake trout (Salvelinus namaycush) population. Modeling res ults indicated that the lower observed PCB concentrations in rainbow t rout compared with lake trout were chiefly due to greater longevity in lake trout. The IBM simulations identified gross growth efficiency, a ssimilation efficiency of PCBs from food, and diet as other important sources of variability in salmonine PCB concentrations.