Effect of Facilitated Recovery and Water Temperature on Capture-Release Survival and Sub-Lethal Responses of Sockeye Salmon

The incidental capture and subsequent release of non-target fish can have sub-lethal and possible lethal consequences. Increased water temperatures can result in additional stress and mortality. The timely recovery of these fish following release is crucial to their subsequent performance. This study integrates the effects of different water temperatures with a catch-and-release event, and explores how recovery may be aided through the assisted ventilation of exercised sockeye salmon. We employed a lab-based experimental approach focused on (i) physiological, (ii) behavioural, and (iii) survival responses. Migrating adult sockeye salmon were obtained by beach seine from the Fraser River and transported to the Fisheries and Oceans Canada Cultus Lake Laboratory. We compared two temperature treatments: a historical average temperature (16°C) and a current peak temperature (21°C) experienced by these summer run sockeye salmon. Two-thirds of all fish were subject to three minutes of manual chasing and one minute of air exposure to simulate the exercise and stress associated with a capture event. Half of these fish were subject to facilitated recovery in which the fish were orientated into a high flow water source for a maximum of one minute to assist ventilation. Thirty minutes after the simulated fisheries encounter, all fish were blood sampled to examine physiological stress parameters. We also made observations of ventilation rates and equilibrium loss. Following experimentation, fish were maintained in their respective temperature treatments for up to five weeks to examine survival. Survival analysis for fish subject to the simulated capture event suggests that the assisted ventilation did not affect survival. Fish held at 21°C experienced 100% mortality within the first three days following treatment, preceding all fish held at 16°C. At 16°C, the simulated capture event resulted in decreased survival and an elevated physiological stress response compared to controls. The females held at 16°C exhibited decreased survival compared to males of the same treatment. The results of the simulated capture events and the ineffectiveness of the recovery technique have catch-and-release management implications. Furthermore, the relatively rapid mortality of all fish following chronic exposure to peak water temperatures highlights the consequences of warmer migration temperatures. Integrating our understanding of thermal and capture stressors with facilitated recovery methods will be important in conserving Fraser River sockeye salmon stocks in the future.