Assessing the Threat of Toxic Contaminants to Early Marine Survival of Chinook Salmon and Steelhead Trout in Puget Sound and the Columbia River Basin

Juvenile Pacific salmon migrating from freshwater through nearshore marine waters to the Pacific Ocean encounter water quality conditions ranging from relatively clean to highly contaminated, depending on their migration route and time spent in contaminated habitats. We sampled juvenile steelhead trout and Chinook salmon at major rivers, nearshore marine bays, and offshore basins of Puget Sound, and juvenile Chinook salmon from the Columbia River to determine if they are exposed to chemical contaminants that may impair their early marine survival. Levels of contaminants measured in wild steelhead from most Puget Sound sample locations were below thresholds for adverse effects to fish health, except for elevated levels of flame retardants in some Nisqually River samples. In contrast, the results indicated that contaminants are likely a significant factor affecting early marine survival of Chinook salmon. Chinook salmon migrating through developed river and bays, and some offshore sites, had concentrations high enough to affect multiple measures of fish health. Results from this work will be used to assess the effectiveness of current toxic reduction strategies and actions, inform future pollution reduction efforts, and enhance recovery of steelhead trout and Chinook salmon.