Surviving Bycatch: Interactions of Temperature, Stressor Severity, and Physiological Disease Processes

For Pacific salmon, lifetime fitness hinges on the completion of an arduous migration and successful spawning at the adult life stage. An understanding of the multiple stressors affecting adult success rates, such as high river temperature and fisheries capture-and-release, is crucial to maintaining productivity of valued Pacific salmon into the future. Furthermore, the mechanisms underpinning premature mortality, such as infectious disease processes, and their interactions with various stressors must also be quantified. We performed long-term holding studies with controlled application of thermal and fisheries stressors, using wild populations of salmon from the Fraser River, BC. Our approach takes non-lethally and lethally sampled tissues from treated and untreated fish throughout the holding period until death, then uses high-throughput qPCR technology on multiple tissue types as well as several blood plasma indices of stress and immunity to quantify changes in fish resilience and microbe productivity over time. By taking a holistic and ecological perspective to disease processes in wild fish, we hope to characterize mechanisms contributing to premature mortality of adult salmon in freshwater, identify microbes of special concern to BC salmon, and develop management recommendations as river temperatures increase across the world and demand for fisheries resources continues to climb.