Marine Survival of Puget Sound Coho Salmon: Deciphering the Climate Signal

Marine Survival of Puget Sound Coho Salmon: Deciphering the Climate Signal

William D. Pinnix

Marine Survival of Puget Sound Coho Salmon: Deciphering the Climate SignalThis is part of Ecosystem Approaches for Fisheries Management
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Description

Each year the State of Washington forecasts the number of adult coho salmon (Oncorhynchus kisutch) that will return to Washington waters. The abundance forecast is conducted jointly by the Washington Department of Fisheries and Wildlife (WDFW) and the Northwest Indian Fisheries Commission in January and February of each year to aid the Pacific Fisheries Management Council in West Coast salmon allocation. This forecast relies on accurate predictions of marine survival combined with hatchery and wild smolt abundance estimates. Historical estimates of the number of hatchery and wild smolts have been quite accurate, whereas marine survival for Puget Sound hatchery coho has been underestimated in the recent past.

Recent studies have implicated localized oceanographic conditions at the time of ocean entry as the critical phase of marine survival for Pacific salmon (Oncorhynchus) species. Coded wire tag (CWT) data are used to calculate time series of coho salmon marine survival for Puget Sound, the Washington coast, west coast of Vancouver Island, and the Strait of Georgia. Several climatic variables related to Puget Sound’s freshwater input are analyzed by principal component analysis.

A conceptual model is presented to visualize how interannual climatic variability affects marine survival of coho salmon in Puget Sound. Changes in climatic variables coincide with changes in marine survival at the decadal scale. The Strait of Georgia and Puget Sound show different patterns in marine survival of hatchery coho salmon due to differences in the freshwater input to volume ratio of these two estuarine systems.

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