PCB CONCENTRATION TRENDS IN LAKE-MICHIGAN COHO (ONCORHYNCHUS-KISUTCH)AND CHINOOK SALMON (O-TSHAWYTSCHA)

Lake Michigan coho (Oncorhynchus kisutch) and chinook salmon (O. tshaw ytscha) PCB concentration data from 1974 to 1990 were examined. The me an and variance of the concentrations exhibited a generally decreasing pattern in each species. Three alternative models, an exponential dec ay model, a double exponential decay model, and an exponential decay m odel with a nonzero asymptote, were fit to the data. The double expone ntial model provided the best fit for both species. Estimated rate coe fficients for this model indicated that an early rapid decrease in PCB s has slowed and that PCBs may currently be increasing in coho and chi nook salmon. These PCB increases may be the indirect result of a decli ne in the alewife (Alosa pseudoharengus) forage base that occurred dur ing the 1980s. Parameter estimates from the nonzero asymptote model su ggested that PCB levels may not decrease substantially below the curre nt 2 mg/kg FDA action level. Significant decreases of PCB concentratio ns in coho and chinook salmon may depend on fisheries management pract ices that promote higher fish growth rates.