Abstract
Lake Michigan coho (Oncorhynchus kisutch) and chinook salmon (O. tshawytscha) PCB concentration data from 1974 to 1990 were examined. The mean and variance of the concentrations exhibited a generally decreasing pattern in each species. Three alternative models, an exponential decay model, a double exponential decay model, and an exponential decay model with a nonzero asymptote, were fit to the data. The double exponential model provided the best fit for both species. Estimated rate coefficients for this model indicated that an early rapid decrease in PCBs has slowed and that PCBs may currently be increasing in coho and chinook salmon. These PCB increases may be the indirect result of a decline in the alewife (Alosa pseudoharengus) forage base that occurred during the 1980s. Parameter estimates from the nonzero asymptote model suggested that PCB levels may not decrease substantially below the current 2 mg/kg FDA action level. Significant decreases of PCB concentrations in coho and chinook salmon may depend on fisheries management practices that promote higher fish growth rates.
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