Facilitating Recovery from Capture Stress in Pacific Salmon

Commercial, recreational, and aboriginal fisheries that target Pacific salmon frequently capture non-target species or stocks of salmon that are co-migrating with the target species. Regulations typically require live release of non-target fish in order to protect populations for which conservation concerns exist. However, fisheries capture can result in severe physiological disturbance, characterized by the use of anaerobic pathways during exhaustive exercise and hypoxia. Given the oxygen debt incurred and the latent effects of a massive release of stress hormones, capture can have impacts on fitness. An efficient and successful physiological recovery from capture is crucial for salmon to be able to resume and complete their already challenging upstream migrations. Therefore, we evaluated the use of recovery gear for facilitating the physiological recovery of Pacific salmon, prior to release from fishing gear in freshwater. A specially designed recovery box, the Fraser box, is already mandatory in marine fisheries for facilitating recovery of coho salmon prior to release, following its validation as a method for reviving coho severely impaired by capture. The Fraser box works by using a powered pump to ram ventilate fish. Using sockeye salmon as a model, we tested three recovery techniques: a low-flow Fraser box (0.2 L s^-1), a high-flow Fraser box (0.9 L s^-1) and an in-river flow-through recovery bag. The recovery bag was cylindrical in shape, 1 m long x 0.2 m in diameter, made of black hypalon, and had coarse mesh ends to enable river flow through the bag and across the gills of the fish. Sockeye were beach seined in the Harrison River (British Columbia), air exposed for 3 minutes to induce severe capture stress, immediately sampled, or placed in one of the three recovery treatments for either 15, 30, 60, or 120 minutes. Following recovery, we quickly assessed reflex actions and sacrificed each individual to sample blood and white muscle. In the laboratory we analyzed physiological indices of stress and exhaustion in plasma and white muscle, and compared those metrics over the 2-hour recovery time course. This study demonstrates that recovery gears can be successfully adapted for use in freshwater to facilitate recovery from capture and in turn, contribute to the sustainability of Pacific salmon fisheries.