Molecular, physiological and behavioural responses to capture in Pacific salmon commercial fisheries : implications for post-release survival of non-target salmon species

With total landings from global commercial fisheries in decline despite increases in fishing effort, there is increasing interest in enhancing fishery sustainability. Estimates suggest that bycatch, the non-target organisms incidentally captured in fisheries, comprises 40 percent of global catches, most of which dies. One means to increase the sustainability of fisheries is to limit bycatch mortality. The research herein uses Pacific salmon purse seine fisheries as a model system to test a series of hypotheses. Merging various techniques in experimental research aboard commercial vessels, I test how both the conditions of capture and intrinsic fish characteristics (e.g., population, sex, maturity) influence post-release survival probability and the magnitude of physiological disruption. The relative importance of intrinsic fish characteristics and capture experience was context dependent, but results suggest that capture situations resulting in dermal injuries are particularly detrimental. In a telemetry study, severity of scale loss predicted mortality and in containment studies, dermal injuries were associated with lasting impairment of blood ion homeostasis and immune function, as indicated by gene expression in the gill. Intrinsic characteristics also played a role: females and less mature fish were more likely to sustain dermal injuries. Capture methods resulting in extended durations of air exposure and to a lesser extent, confinement during capture, also caused substantial cellular disruption. Air exposure led to widespread down-regulation of stress and gill immune genes for up to 5 days, which I contend is an energy-saving strategy. Through evaluating physiological parameters both during and after exposure to capture stressors, I also identified thresholds in capacities to cope with capture stress, information that is valuable for informing best handling practices that could improve fish survival. Finally, through interviews with fishers, I revealed that increased transparency between management and fishers may improve compliance with suggested best handling practices. Collectively the present work improves fundamental knowledge of the effects of acute stress on the physiology of fish and can be directly applied to improving the welfare of discarded fishes, particularly in purse seine fisheries targeting Pacific salmon.Forestry, Faculty ofGraduat