Fish caught in the fall exhibited a smaller rate
of increase in PCB concentration with length, but small fish had larger PCB concentrations than similar size fish caught in the summer. Large fish had similar PCB concentrations in both seasons. The interaction between chinook length and % lipid was very similar to the corresponding interaction found for coho: there was a steeper rate of increase in PCB concentration with body length for fish with low values of % lipid. As with models for coho, the chinook model with interactions among predictor variables reflected minor changes in the relationships found in the simpler model without interactions. Models developed using coho and chinook PCB records from 1975 to 2010 show a steep selleck inhibitor decline in filet total PCB concentrations prior to the mid-1980s and less dramatic declines after the mid-1980s. We found the best models for both species included piecewise linear time trends, body length, % lipid in filet, and collection season as predictor variables. The intersection of the two trends was 1984 for coho salmon
and 1985 for chinook. Our data demonstrates a dramatic decline in PCB concentrations before the mid-1980s of − 16.7% and − 23.9% per year for chinook and coho, respectively, likely reflecting implementation of restrictions on PCBs. For the period between the mid-1980s to 2010, PCB concentrations declined at a rate of − 4.0% per year (95% CI: − 4.4% to − 3.6%) and − 2.6 per year (95% CI: − 3.3% to − 1.9%) for chinook and coho, respectively. Chang et al. (2012) reviewed recent check details estimates of temporal trends of PCBs in a variety of media types (air, sediment, water, gull eggs, lake trout) and while the time period examined varied, annual decreases have been estimated to
be less than 10% over the Great Lakes. They estimated that whole body PCBs declined 8.1% annually in the long-lived and high lipid SPTLC1 Lake Michigan lake trout during the period 1999–2009. Because lake trout may live up to 20 years (Becker, 1983), these trend estimates may still reflect dramatic PCB ban effects. French et al. (2006) found exponential decay models best described temporal trends in the sum of PCB congeners in Lake Ontario chinook and coho salmon over the time period 1983 to 2003. The exponential decay rates estimated by French et al. equate to annual percentage changes of − 7.87% for chinook and − 9.61% for coho. While PCB trends exhibited by different Lake Michigan species, media or time periods are expected to differ (Hu et al., 2011 and Lamon et al., 2000), our estimates may best reflect the more recent PCB reductions in Michigan salmon. This information should be useful in evaluating contemporary efforts to reduce PCB sources to Lake Michigan.