Responses of Okanagan Sockeye Salmon Adults to Environmental Extremes Encountered during Freshwater Migration

Okanagan sockeye salmon exist at the southern end of this species range and face an arduous 900 km freshwater migration to reach spawning grounds in British Columbia. Annual to seasonal fluctuations in environmental conditions (temperature, river discharge, oxygen) pose variable challenges to success within their freshwater migration corridor. Historic and recent year studies suggest that temperature differentials at the confluence of the Columbia and Okanagan rivers may induce migration delays in Wells Pool varying from 0 to >50 days in a given year. Further, multiyear mean delays appear to vary in accordance with Pacific Decadal Oscillation (PDO) phase changes. By contrast, temperature and oxygen conditions in the south and central basins of Osoyoos Lake present an acutely stressful set of conditions that migrating sockeye must endure in all years in order to reach the north basin of Osoyoos Lake where sockeye may hold for weeks to months prior to spawning. Newly documented behavioural responses of sockeye to seasonal variations in temperature and oxygen gradients while holding and maturing in the north basin of Osoyoos Lake provide important clues to limits on the adaptive capacity of sockeye salmon to survive current and future environmental extremes associated with climate variation and change.