Pollutant transport by introduced Pacific salmon to Great Lakes tributaries

Persistent organic pollutants can be transported globally through both physical processes and biological transport.  We assessed the magnitude and distribution of pollutant transport to Great Lakes tributaries by migratory Pacific salmon (Oncorhynchus spp.).  In 10 streams, brook trout (Salvelinus fontinalis), sculpin (Cottus spp.), and blacknose dace (Rhinichthys atratulus) were sampled from stream reaches with or without salmon and analyzed for polychlorinated biphenyls (PCBs), polybrominated biphenyl ethers (PBDEs), and 1,1-dichloro-2,2-bis(p-chlorophenyl) ethylene (DDE).  Pollutant levels were nearly 6x higher in salmon from Lake Michigan than from Lake Superior, and pollutant levels in stream-resident fish were positively correlated with salmon contamination.  In Lake Michigan, stream fish were 10-100x more contaminated in salmon reaches than in non-salmon reaches, while stream fish from Lake Superior tributaries were 1.2-3.3x more contaminated in salmon reaches.  Gut content analysis suggests that consumption of salmon material is the primary route of contaminant uptake.  These data suggest that salmon runs bring a significant influx of contaminants to streams, but the magnitude of contamination varies considerably between lake basins.  Management practices in Great Lakes tributaries, such as dam removal, have the potential to spread these contaminants to new stream reaches.