Climate warming and high salmon migration mortality

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Pacific salmon support the most valuable commercial and recreational fisheries in western Canada generating over $1 billion of revenue annually. They are an important component of the food chain, are integral to mythology, spiritual integrity, and local economies of Pacific coast First Nations, and are icons for the general public, with abundant salmon confirming healthy and pristine environments. Most stocks of Pacific salmon now encounter warmer rivers during their up-river spawning migration than in any time since records were kept. The Fraser River is Canada's most productive salmon system and has experienced in the past 10 years eight of the hottest summer water temperatures on record, and climate models predict even warmer temperatures in the near future. Associated with these high temperatures have been high levels of migration mortality costing the fishery significantly with millions offish disappearing during migrations or dying unspawned. This phenomenon constitutes a severe conservation risk and puts the sustainability of Fraser sockeye in doubt. New policies have shifted sockeye salmon harvesting from cool ocean to warm river locations which puts salmon in double jeopardy if they escape or are released from capture because struggling under high temperatures can lead to mortality hours after release. We will conduct experiments to establish criteria which can predict mortality rates from expected thermal exposure and interactions with different levels of non-retention in-river fishing, and to assess effects of adult migratory thermal exposure on eggs and offspring. Our findings will provide important information that will be used to help the fisheries management agencies, our partners in this project, with their task of predicting migration mortality, predicting future stock sizes, and managing habitat to conserve the resource.