Salish Sea salmon and steelhead survival trends

Investigating Agencies: Washington Department of Fish and Wildlife, Department of Fisheries and Oceans, NOAA Northwest Fisheries Science Center, Tulalip Tribes, Lummi Nation, Skagit River System Cooperative, Nisqually Tribe

Chinook, coho, and steelhead marine survival time series were aggregated and analyzed to determine:

  1. What are the marine survival trends for Salish Sea salmon and steelhead populations? How do these trends compare to nearby populations outside of the Salish Sea (i. e., control group)?
  2. Does survival differ for stocks entering the Salish Sea within different sub-basins (in particular, comparing oceanographic basins of Puget Sound to the Strait of Georgia)? If so, where, when, and to what degree has it varied?
  3. Does marine survival more strongly predict adult returns than freshwater survival?
  4. How much does marine survival differ between hatchery stocks and naturally spawning populations?
Coho marine survival over time. Blue represents wild stocks. Image credit Zimmerman et al. 2015.

Coho marine survival has consistently declined within the Salish Sea since the 1970s, whereas coastal coho populations do not show this pattern. In all areas, wild coho survived better than hatchery coho. Marine survival patterns were strongly synchronized among neighboring populations (i.e., populations geographically close to each other survived at similar rates), suggesting that early marine conditions impact overall coho survival to adulthood. Read more here:

Chinook marine survival patterns also differed between Salish Sea and coastal populations. Salish Sea chinook displayed high inter-population variability, and many Salish Sea populations exhibited sharp declines and/or consistently low survival since the early 1990s.

Steelhead marine survival patterns differed among coastal, Columbia River, Strait of Juan de Fuca, and Puget Sound populations. Survival declined over time for all regions except Juan de Fuca, and Puget Sound populations have had the lowest survival of any region since the 1990s. Neighboring populations had similar survival patterns, indicating that early marine conditions are important to steelhead survival.

These analyses provide the framework and foundation for future analyses to determine how ecosystem conditions affect survival and contribute significantly to the baseline data required for ongoing and proposed analysis and modeling activities, listed below. Participants are also interested in using the outcome of this work as a template for long-term monitoring.