Impact and Adaptation Responses of Okanagan River Sockeye Salmon (<i>Oncorhynchus nerka</i>) to Climate Variation and Change Effects During Freshwater Migration: Stock Restoration and Fisheries Management Implications

Abstract

We summarized existing knowledge on behavioural and physiological responses of Okanagan sockeye salmon (O. nerka) adults to annual and seasonal variations in aquatic thermal regimes during migration. This enabled us to identify an underlying set of ‘decision rules ’ as a biophysical model of how temperature mediates en–route delays as a specific element of annual migrations by sockeye salmon. Several sets of results indicate that adult sockeye migrations stop as seasonal water temperatures increase and exceed 21oC and then restart when temperatures decrease and fall below 21oC. Model predictions of annual variations in the duration of migratory delay exhibited close agreement with independent estimates of observed delays available from a subset of years (predicted delay = 1.23 observed delay + 2.08, r2 = 0.92, p &amp;lt; 0.001, n = 10). We applied the model in a retrospective analysis of the likely impacts of climate variation and change events on adult sockeye migrations in freshwater over the 70 plus year interval between 1924 and 1998. Results indicate that migration delays for a significant portion of the sockeye population averaged