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UBC Theses and Dissertations

Influences of temperature on the mortality and physiological impairment of sockeye salmon after simulated capture and release Gale, Marika Kirstin


Pacific salmon experience intense fishing pressure as they commence their freshwater spawning migration, frequently encountering commercial net fisheries and recreational hook and line gear. Untold numbers of fish escape by their own volition or are released by fishers at a range of water temperatures, including those above metabolic and physiological optimums. This thesis focuses on the mortality and sublethal consequences of escape or release from fishing gears by migrating adult Pacific salmon, with a specific focus on how temperature mediates those effects. The role of temperature in the capture and release of fish was investigated in a comprehensive literature review. This revealed that 70% of studies examining mortality or sublethal effects at various temperatures found both to be magnified at warmer temperatures. Collectively, the results suggest that capture-release mortality increases at temperatures within, rather than above, species-specific thermal preferenda. Notably, there were no studies examining temperature effects on capture-release for adult migrating Pacific salmon. In two experiments, migrating adult sockeye salmon were intercepted during the early part of their freshwater migration held in a laboratory at three temperatures corresponding with the range of temperatures spanning the historic, current and predicted future migration conditions experienced by their run-timing group (13°C, 19°C, 21°C for summer-run fish in 2009, and 13°C, 16°C, 19°C for late-run fish in 2008). Fish were exposed to a simulated capture treatment including three minutes of burst exercise ± 60 seconds of air exposure. In both experiments, simulated capture treatments resulted in elevations of plasma lactate concentrations, most markedly after air exposure. The highest mortality was seen in the late-run females at 19°C. Late-run fish who died within 24 hours of capture treatment were characterized by higher hematocrit, plasma lactate and cortisol, and lower glucose, sodium and chloride concentrations than survivors. Air exposure and warm temperatures were associated with longer equilibrium loss and slower ventilation rates post-treatment, which significantly predicted 24-hour survival in late-run fish. Collectively, these results indicate that released or escaped sockeye salmon may be at higher mortality risk when river temperatures are exceedingly high, and that reducing or eliminating air exposure may result in greater survival.

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