Ten Years of Lab and Telemetry Studies on Canada's Largest Salmon River Finds Exceptionally High Mortality of ‘Handled' Migrating Female Sockeye: The Need for Sex-Specific Guidelines in Catch and Release Fisheries?

Over the past 10 years our research group has ‘handled’ several thousand adult Fraser River salmon during their homeward migration.   This handling has involved capturing fish using a variety of gear types, implanting physiological or conventional transmitters, and tracking them to study migration success, and lab studies examining survival and physiological recovery following exhaustive exercise. We routinely find that when ‘handled’ individuals encounter challenging conditions (e.g. high or turbulent flows, high temperatures, confinement) towards the end of their migratory period, females suffer 2-5X higher mortality than males.  The causes of this phenomenon could be multiplicative as females must allocate large energy levels to gonads and do not eat so could exhaust reserves, they maintain high levels of circulating plasma cortisol which enhances physiological stress responses including making them more immunocompromised and less resistant to pathogens, and they have relatively poorer cardiac performance under fast swimming speeds.  Any of these issues following capture-release could accelerate natural morality rates when migratory conditions become arduous.  The implications of this to catch and release fisheries, and conservation will be reviewed.