Pacific salmon and steelhead : life in a changing winter ocean

How Pacific salmon and steelhead (Oncorhynchus spp.) respond to climate-driven changes in their oceanic environment is highly uncertain, in part due to limited information on winter distribution in international waters (high seas) of the North Pacific Ocean and Bering Sea. We review what is known and summarize what should be known to properly address the question: Where do Pacific salmon go in the high seas during winter and why, and how might this be affected by climate change? Historical high-seas research (1950s–1970s, all seasons) discovered that there are species and stock-specific distributions in the high seas; winter survey results provided some clues as to important winter locations and dominant oceanographic features of winter habitat. In succeeding decades (1980–2015), new fisheries-oceanographic survey methods, stock-identification techniques, remote-sensing technologies, and analytical approaches have enabled us to expand our knowledge of the winter distribution and ecology of salmon, although empirical data are still very limited. In general, we learned that the ‘why’ of ocean distribution of salmon is complex and variable, depending on spatio-temporal scale and synergies among heredity, environment, population dynamics, and phenotypic plasticity. The development of quantitative multispecies, multistage models of salmon ocean distribution linked to oceanographic features would help to identify key factors influencing winter distribution and improve understanding of potential climate change effects.