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Physiological, behavioural and survival effects of assisting the post-capture ventilation of adult sockeye salmon exposed to capture and release in fresh water Robinson, Kendra Alexis


Fish that are released from fisheries capture exhibit physiological and behavioural changes that can result in mortality. The ability to release fish that do not experience subsequent fitness consequences is fundamental to fisheries conservation and management tools that mandate live release. Thus, researchers have evaluated methods that fishers can use to reduce the potential for negative capture-related effects. Indeed, modifying capture and landing practices can limit the severity of the physiological and behavioural impairments. Moreover, release techniques that enhance the metabolic recovery process essential for mitigating capture-related physiological changes may help to enhance survival. Because this essential recovery process requires oxygen consumption that exceeds basal metabolic needs, I evaluated a ventilation assistance technique that forced a high flow of water over the fish’s gills in an attempt to provide additional oxygen. This assisted ventilation technique mimics manual recovery attempts that are recommended by fisheries managers and often employed by recreational anglers. The physiological, behavioural and survival responses of adult migrating Fraser River sockeye salmon (Oncorhynchus nerka) to capture and release, with and without ventilation assistance, were assessed in laboratory and field experiments. A simulation of capture and release consisting of 3 minutes of strenuous exercise and 1 minute of air exposure resulted in significant physiological impairment in the laboratory experiment. In a field experiment, this simulation resulted in an approximate 30% overall reduction in post-release survival to reach natal spawning grounds. Female fish exposed to simulated capture and release exhibited poorer survival relative to control females and males of all treatments in both of these experiments. The 1-minute assisted ventilation technique did not enhance survival. In fact, further reductions in survival were observed in the laboratory experiment for females subjected to ventilation assistance before release from capture. Capture and release can result in delayed mortality and it appears that a recovery technique recommended by fisheries managers to recreational fishers does not help to reduce capture-related mortality. Mitigating negative capture-and-release effects by disseminating capture and landing best practices, while incorporating scientifically-defensible post-capture mortality rates into management plans, may be the best approach to meeting conservation and management objectives.

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