Marine Distribution, Life History Traits, and the Accumulation of Polychlorinated Biphenyls in Chinook Salmon from Puget Sound, Washington

Polychlorinated biphenyl (PCB) levels and the factors affecting PCB accumulation in subadult and maturing Chinook salmon Oncorhynchus tshawytscha from Puget Sound were characterized. Specifically, we (1) determined PCB levels in Chinook salmon from Puget Sound and compared them with levels in Chinook salmon front other West Coast populations, (2) determined whether PCB accumulation mainly occurred in the freshwater or marine habitats, and (3) quantified the relative importance of fish age, fish size (fork length), lipid content. and saltwater age (the number of winters spent in saltwater) on PCB concentration. The average PCB concentration measured in skinless muscle tissue samples of subadult and maturing Chinook salmon collected from Puget Sound was 53 ng/g (wet weight), which was 3-5 times higher than those measured in six other populations of Chinook salmon on the West Coast of North America. Concentrations in the Puget Sound samples varied from 10 to 220 ng/g. A comparison of PCB body burdens between subyearling smolts and returning adults revealed that almost all of the PCBs (>96%) were accumulated in the marine habitats. Surprisingly. although PCBs were mostly accumulated in marine habitats. PCB exposure was lowest in the largest fish that spent the most little in saltwater. Collectively, saltwater age. fish size, and lipids only accounted for 37% of the observed variation in PCB concentration, indicating that some other attribute of the fish's marine ecology accounted for the variation in PCB levels among Puget Sound Chinook salmon and for their elevated PCB levels relative to other West Coast populations. We hypothesized that residency in the contaminated Puget Sound environment was a major factor contributing to the higher and more variable PCB concentrations in these fish. This hypothesis was supported with an independent data set from a fishery assessment model, which estimated that 29% of subyearling Chinook-salmon and 45% of yearling out-migrants from Puget Sound displayed resident behavior.