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Freshwater Production and Survival of Puget Sound Salmonids

  Upper Dungeness River

Declining numbers of salmon, steelhead, and char in the Pacific Northwest have been of increasing concern for natural resource managers. In the Puget Sound region, four species – Chinook, summer chum, steelhead and bull trout – are currently listed as “threatened” under the Endangered Species Act. At the time of listing, little was known about the juvenile abundance or diversity for many populations of these Puget Sound species.

Juvenile migrants are the product of the freshwater environment and determine the number of fish entering the ocean environment, recruiting into fisheries, and returning to the river to spawn. The number and diversity of juvenile migrants are impacted by the combined management of hatchery, harvest, habitat and hydropower. For example, when the number of spawners is too low, the number of juvenile migrants will also be low. In this case, an effective management action may be to reduce harvest and allow more spawners to return to the river. However, when the number of spawners is high enough to fully use available habitat, the number of juvenile migrants is primarily limited by interactions in the freshwater environment. Under this second scenario, effective management actions may be to improve freshwater habitat or minimize interactions between hatchery and wild spawners.

In order to improve understanding of abundance, survival, and diversity of salmon, trout, and char in Puget Sound, the Wild Salmonid Production Evaluation (WSPE) Unit has implemented long-term studies in multiple watersheds. Juvenile studies are currently conducted in the Skagit, Lake Washington, Green, Nisqually, Duckabush, and Dungeness rivers. An adult study was initiated in the Elwha River beginning in the summer of 2010.

Questions currently addressed by this research program include:

  • What factors determine juvenile abundance and life history diversity of Puget Sound Chinook?
  • How do natural and hatchery fish contribute to re-colonization of the Elwha River watershed?
  • How do stream temperatures influence the outmigration timing of Hood Canal summer chum?
  • What limits freshwater survival of Lake Washington sockeye?
  • How do the number of pink and chum salmon influence anadromous bull trout?