Wednesday, November 18, 2009

Research on Puget Sound Marine Survival

Early marine survival is a critical life history stage for outmigrating salmon and steelhead smolts, and growth and survival during the first few weeks at sea plays a large role in determining the adult return within a given cohort. Biologists in our area have long suspected that low marine survival in outmigrating smolts is a large part of why Puget Sound wild steelhead are continuing to decline. A new paper by NOAA researcher Megan Moore and coauthors Barry Berejikian and Eugene Tezak may provides some insight into patterns of migration and survival during the first few weeks of ocean life. The group used acoustic tags, which they implanted in outmigrating smolts. These tags allowed them to track survival and movement as fish passed out of Hood Canal and ultimately out the Strait of Juan De Fuca. Results show high early mortality and in 2006 only 31% of the outmigrating smolts even passed the Strait of Juan de Fuca acoustic array (about half way out), and mortality probably declined substantially after the first few weeks of life. Still, normal lifetime marine survival in healthy populations of steelhead in typically between 10 adn 25% and if almost 70% of fish die within the first few weeks at sea it is unlikley that their survival over the next two to three years is high enough to see 10% lifetime marine survival.

As a consequence of this low marine survival, many populations of steelhead in Puget Sound may still be producing as many smolts as they were during periods of better adult returns. However because of low marine survival, the return on the same number of smolts is substantially lower. Their findings are in line with a number of studies of early marine survival in Southern BC, an area which has seen concurrent declines in wild steelhead productivity since the mid 1990s. Melnychuk et al (2007) found nearly identical early marine survival for smolts from the Cheakamus and Squamish Rivers.

Lower marine survival is likely being driven by a number of factors including variation in food availability, predation pressure, and competition for resources with hatchery steelhead and salmon. See the abstract of the paper at AFS Journals

Those interested in reading the full paper or more info on the current reserach relating to early marine survival can email us at

Also, more information on the Hood Canal Steelhead Project on Long Live the Kings website.

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