For more information on species & ecosystem science:

Wildlife Science
360-902-2515
wildthing@dfw.wa.gov

Fish Science
360-902-2700
fishpgm@dfw.wa.gov

Habitat Science
360-902-2534
habitatprogram@dfw.wa.gov

 

Wild Coho Production and Survival

 

Lead Scientist: Mara Zimmerman

Ecoregions: Puget Trough, Northwest Coast

Ecological Systems: Not available for instream habitats  

   
 
Male coho spawner caught in upstream weir
   
 
Coho migrate to the upper most extents of each watershed
to spawn
   

The Wild Salmonid Production Evaluation (WSPE) Unit began studies of wild coho salmon in Washington State in the late 1970s. The initial purpose was to determine the freshwater capacity for wild coho stocks. Freshwater capacity is the maximum number of juveniles that can be produced during the freshwater life stage. This capacity is defined by the characteristics of the watershed, although an adequate number of spawners are needed to maximize juvenile production. Understanding freshwater capacity is important for harvest management because the number of juveniles entering the ocean environment limits the number of fish that will recruit into the fishery. Therefore, defining freshwater capacity and identifying the number of spawners needed to adequately seed the watershed will benefit both wild coho stocks and the fishery.

Coho production and survival is measured at two life stages – smolt and spawner. Smolts are measured using juvenile traps placed near the mouth of the watershed. The WSPE Unit has measured wild coho smolt production in over 20 watersheds in Washington State. These watersheds have ranged from massive systems such as the Skagit and Chehalis rivers to small lowland watersheds such as Big Beef and Little Anderson creeks. Within watersheds, freshwater production typically varies 2 to 4-fold among years. Most of the inter-annual variability can be explained by stream flows at key life stages (spawning, incubation, summer rearing, and overwinter rearing). In addition, coho in Deschutes River have demonstrated remarkable freshwater life history diversity in response to depressed abundance of this stock.

Marine survival of wild coho is estimated from long-term monitoring stations in Puget Sound (Deschutes River, Baker River, Big Beef Creek) and coastal Washington (Bingham Creek). Smolts are coded-wire tagged and released during their downstream migration. Coded-wire tags are recovered during sampling of coast-wide fisheries and from coho intercepted in upstream weir traps. Marine survival is the sum of harvest rate and escapement rate for each group of tagged fish. The populations selected for this study were from watersheds with fixed weir or fish ladder structures. These structures allow for a complete census of returning spawners and greatly improve the accuracy of adult coho data. Correlations between jack (age-2) and adult (age-3) return rates are identified in each data set and are used to predict adult marine survival based on a given year’s jack returns. However, the jack-adult correlation has not been consistent over time. We are currently examining metrics of ocean conditions in order to identify additional, and potentially more consistent, predictors of coho marine survival.

Projects

  • Deschutes River
  • Baker River (Skagit)
  • Big Beef Creek
  • Bingham Creek
  • Chehalis River
  • Elk Creek (historical)
  • SF Skykomish River (historical)
  • Dickey & Bogachiel Rivers (historical)

Advisory Wild Coho Forecasts