Impaired health of juvenile Pacific salmon migrating through contaminated estuaries

Juvenile chinook salmon (Oncorhynchus tshawytscha) and chum salmon (Oncorhynchus keta) accumulate polycyclic aromatic hydrocarbons, polychlorinated biphenyls and other chemical contaminants in tissues, fluids and stomach contents while utilizing contaminated estuaries of Puget Sound during their out-migration from fresh water to open ocean. Field studies show that they have impaired health (reduced immunocompetence, increased mortality after disease challenge, reduced growth) resulting from migration through these areas. A series of laboratory investigations has shown that all of these effects can be elicited by exposure to either specific compounds or classes of compounds present in the contaminated waterways, or to complex mixtures of chemicals extracted from the sediments of the waterways. These results provide corroboration for a cause-and-effect relationship between impaired health of Pacific salmon and their exposure to chemical contaminants from urban estuaries. Specific information on the nature of the dose–response relationship is lacking, but studies are planned to address that question. With the impending listing of Pacific salmon stocks in Puget Sound under the Endangered Species Act, these studies take on added significance.