Distinct Contaminant Fingerprints in Chinook Salmon Reflect Their Marine Distribution and Feeding

Levels of persistent organic pollutants (POPs) in Pacific salmon and other fishes depend on where they live and what they eat.  Salmon may be exposed to contaminants in freshwater and estuarine habitats but most of the adult body burden of POPs is accumulated in marine habitats where almost all growth occurs. Adult Chinook salmon may accumulate higher POP concentrations than other salmon species because their more coastal distribution keeps them in proximity to land-based contaminant sources, they feed at a higher trophic level which exposes them to greater levels of POPs in prey biomagnified through the food web, and their high fat content retains lipophilic contaminants.  Chinook salmon populations feeding along more developed coastlines in close proximity to land-based sources contaminants may accumulate POPs at sufficient concentrations to impact their health and also the health of their predators, including humans and killer whales. To evaluate the extent to which POPs accumulate in Chinook salmon, we measured whole body concentration of POPs in sub-adult and adult fish from 5 populations originating from streams ranging from northern British Columbia to Puget Sound and northern California. Chinook salmon feeding in marine waters near land-based sources of contaminants had higher concentrations of several POPs.  For example, levels of PCBs and PBDEs were highest in Chinook salmon that originated from and resided in Puget Sound, followed by Puget Sound-origin populations that migrated to the ocean, and were lowest in populations from northern British Columbia, distant from urban areas.  DDT levels were highest in Chinook salmon populations originating from California that migrate and feed northward off the coast of California and Oregon, reflecting greater use of that pesticide in that region.  POP levels among Chinook salmon populations were not correlated biological traits such as fat content or trophic status.  The relative abundance of six POP classes (PCBs, PBDEs, DDT, HCB, Chlordanes, and HCHs) among these Chinook salmon populations provided distinct chemical fingerprints of their exposure to land-based sources of contaminants and contaminated prey. The marine distributions inferred from these distinct contaminant fingerprints were consistent with independent assessments of the migration patterns and distribution of the populations.  The contaminant fingerprints identified here may therefore be a useful comparative tool to help elucidate marine distribution or migration patterns of other Pacific salmon species, other Chinook salmon populations, and individuals within populations.