Ecological Indicators of Chinook, Coho, and Steelhead Marine Survival in Puget Sound, Washington

Pacific salmon stocks are known for their high variability in marine survival and the resultant difficulty in forecasting stock size to support sustainable harvest management. This variability has sometimes resulted in poor forecasts of adult returns, a situation that can complicate conservation and constrain commercial, tribal, and recreational fishing. Consequently, much interest has developed across the Pacific Coast in using ecosystem indicators to improve predictions of productivity and adult abundance. We describe an effort to apply a suite of ecosystem indicators to coho, steelhead and Chinook salmon stocks in Puget Sound. Anadromous salmon stocks spawn in six sub-basins with distinct geomorphology and oceanography. We compiled climate, hydrologic, and biotic indicators from the late 1970s to the present, and tested for temporal and spatial covariation among indicators and covariation of indicator sets with sub-basin-specific survival estimates. Using this information, we developed a suite of indicators specific to sub-basins, and tested their predictive power by applying them to independent datasets. We discuss the potential utility of using these indicators as forecasting tools in the face of long-term population declines of the three species.