Salish Sea Marine Survival Project researchers studied outmigrating steelhead smolts from the Skagit, Snohomish, Green/Duwamish, and Nisqually rivers and associated marine habitats in Puget Sound. They found high levels of a parasite called Nanophyetus salmincola in steelhead from the Green/Duwamish and Nisqually watersheds. This parasite burrows through the skin of the fish and forms cysts in various organs: primarily the posterior kidney, but also gills, heart, and muscle tissue. The tissue damage caused by the parasite can reduce fish swimming performance and high parasite levels can cause organ damage severe enough to kill the fish. Researchers also found that steelhead in the Nisqually and Green/Duwamish rivers were exposed to persistent organic pollutants (POPs); POP levels in fish tissue exceeded levels associated with increased disease susceptibility and adverse effects. Parasites and POPs likely contribute to low juvenile steelhead survival within Puget Sound. Read more: Chen et al. (2018) Infection by Nanophyetus salmincola and toxic contaminant exposure in out-migrating steelhead from Puget Sound, Washington: implications for early marine survival. DOI: 10.1002/aah.10017
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