MODELING CHANGES IN GROWTH AND DIET ON POLYCHLORINATED BIPHENYL BIOACCUMULATION IN COREGONUS-HOYI

Restrictions on the release of PCBs into the environment began in the early 1970s, resulting in reduced PCB concentrations in Lake Michigan bloaters (Coregonus hoyi). However, since 1980, PCB concentrations in bloater have declined only slightly. The bloater population also incre ased 40-fold during 1970 through 1984, resulting in a diet shift and a density-dependent decline in growth. Our goal was to determine how th ese changes in diet and growth may have affected PCB accumulation in L ake Michigan bloater. We evaluated the consequences of these two chang es on bloater PCB concentrations by developing a bioenergetics-based P CB bioaccumulation model. Bloater PCB concentrations increased little when we increased the amount of Diporeia hoyi, the most contaminated p rey, in the bloater diet. By comparing constant growth (similar to tho se of the 1970s) to observed decline in growth rates, we found that lo wer growth rates during the 1980s placed older, more contaminated bloa ters in the size range most vulnerable to predators and in the size ra nge sampled by PCB monitoring programs. Bloater PCB concentration tren ds may be influenced by the sampling methodology of the United States Geological Survey. If fish PCB trends are to be used as an indicator o f system-level PCB trends, sampling should include a representative sa mple of fish of known age from the population.