Potential climate change impacts on thermal habitats of Pacific salmon (Oncorhynchus spp.) 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 evaluated the effects of natural climate variability and projected changes under three Intergovernmental Panel on Climate Change scenarios of future greenhouse gas emissions. Changes in high-seas habitat due to natural climatic variation in 20th century were small relative to that under anthropogenic climate change scenarios for the middle to late 21st century. Under a multimodel ensemble average of global climate model outputs using A1B (medium) emissions scenario for the entire study area (North Pacific and part of Arctic Ocean), projected winter habitats of sockeye (Oncorhynchus nerka) decreased by 38%, and summer habitat decreased by 86% for Chinook (Oncorhynchus tshawytscha), 45% for sockeye, 36% for steelhead (Oncorhynchus mykiss), 30% for coho (Oncorhynchus kisutch), 30% for pink (Oncorhynchus gorbuscha), and 29% for chum (Oncorhynchus keta) salmon by 2100. Reductions were 25% lower for B1 (lower) emissions and 7% higher for A2 (higher) emissions scenarios. Projected habitat losses were largest in the Gulf of Alaska and western and central subarctic North Pacific. Nearly complete losses of Gulf of Alaska habitat for sockeye in both seasons and Chinook in summer raise important policy issues for North American fishery managers and governments.