Influence of Postcapture Ventilation Assistance on Migration Success of Adult Sockeye Salmon following Capture and Release

Abstract

AbstractCatch and release is a tactic employed in recreational fisheries to help conserve and sustain fish populations, but postrelease mortality can occur when fish fail to recover from the stress and exhaustion of capture. Depending on factors like the duration of the stressor and whether air exposure occurs, fish can be lethargic or have negative equilibrium upon release; some anglers are motivated to attempt to manually revive fish upon release by assisting with water flow across the gills. Indeed, some management agencies and angling groups recommend different recovery techniques, but very little scientifically defensible evidence exists about the utility of assisted ventilation. We conducted two separate field experiments on Sockeye Salmon Oncorhynchus nerka in the lower Fraser River basin in which fish were (1) exposed to a standardized exercise stressor with air exposure or (2) angled by volunteer anglers and air exposed, with a subset of fish in each experiment then being provided with 1 min of assisted ventilation before release with a radio transmitter. Assisted ventilation took the form of simply holding the fish below the water surface, facing into a flow of ∼0.5 m/s. Postrelease behavior and migration success were examined in both experiments by radio‐tracking fish, using a combination of fixed stations and manual tracking. Our results from both experiments provide no support for the utility of this revival technique in benefiting the migration success of Sockeye Salmon exhausted from a capture‐and‐release event. Future experiments should test the survival and physiological benefits of different revival techniques and durations for fish at different levels of postcapture impairment.