Fraser River Sockeye Salmon in an Era of Climate Change

Climate change induced increases in summer water temperature have been repeatedly associated with elevated mortality of adult Fraser River sockeye salmon (Oncorhynchus nerka) during their upriver spawning migration. There are over 100 genetically and geographically distinct populations within the Fraser River watershed which encounter different migration distances (100-1,100 km), elevation gain (10-1,200 m), river temperature (9-22°C) and river flow (2,000-10,000 m³ s^-1). We hypothesized that sockeye salmon populations have locally adapted through natural selection to meet their specific migration challenges. Populations with the most challenging migrations have higher somatic energy at the start of the migration, fewer eggs, a more fusiform body shape, higher swim performance, greater aerobic scope, greater cardiac scope, and larger hearts with an enhanced oxygen supply via the coronary circulation. In addition, functional thermal tolerance has been determined for 9 of the major populations. Chilko sockeye salmon emerged as the champions of high temperature tolerance, able to maintain maximal cardiorespiratory performance up to 21^oC. These results are currently being used by management agencies to help predict escapement and manage fisheries.