Scenarios for Climate Change Impacts on Thermal High Seas Habitats of Pacific Salmon in the North Pacific Ocean and Adjacent Seas

We developed spatially-explicit representations for seasonal high-seas (open ocean) thermal habitats for six species of Pacific salmon (Oncorhynchus spp.), and then used these to evaluate the effects of natural climate variability and predicted changes under three IPCC scenarios of future greenhouse gas emissions. Changes in the high-seas thermal habitat of Pacific salmon (Oncorhynchus spp.) due to natural climatic variation in the 20th Century were small relative to those under scenarios of anthropogenic climate change for the middle to late 21st Century. Under a multi-model ensemble average of global climate model (GCM) outputs using the A1B (medium) emissions scenario, projected winter habitats of sockeye (O. nerka) decreased by 38%, and summer habitat decreased by 86% for Chinook (O. tshawytscha), 45% for sockeye, 36% for steelhead (O. mykiss), 30% for coho (O. kisutch), 30% for pink (O. gorbuscha), and 29% for chum (O. keta) salmon by 2100. Projected decreases were 25% lower for B1 (lower) emissions and 7% higher for A2 (higher) emissions scenarios. Projected habitat losses in both seasons were largest in the Gulf of Alaska and subarctic North Pacific. The potential for substantial losses of high-seas salmon habitat area in the future highlight the need to develop new tools and consider alternative strategies for salmon management.