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Hydro-system related mortality and in-lake behaviour of migrating adult sockeye salmon in the Seton-Anderson Watershed, British Columbia Roscoe, David William


Pacific salmon carry out long distance spawning migrations from ocean feeding grounds to natal freshwater streams. Because many salmon rivers are dammed, fishways are required to enable individuals to pass through dams and reach upstream spawning areas. However, many fishways are ineffective, preventing or delaying upstream passage, suggesting a need to monitor and evaluate these facilities. I conducted a literature review of studies evaluating the effectiveness of fishways to assess what taxa and life-stages have been studied, the questions asked during evaluation, and how these varied by time or geographic location. The majority of studies focused on adult fishes (68%) and the order Salmoniformes (58%). Many studies evaluated exogenous mechanisms of passage failure, such as environmental or structural factors (69%). Few studies examined endogenous (i.e. physiological) factors or post-passage consequences, information that is necessary to understand passage failure and inform mitigation strategies. A field study was carried out to evaluate the impact of a dam and fishway on the spawning migrations of sockeye salmon in the Seton-Anderson watershed in British Columbia. I used acoustic telemetry, non-lethal biopsies, and an experimental approach, releasing fish either up- or down-stream of the dam and comparing behaviour and mortality between the two groups. Fishway passage efficiency was 80% and most failure was associated with failing to locate the entrance. Attraction to the fishway entrance varied with water discharge volume from the dam, with the longest delays and highest failure rate at the highest discharge. Fish released downstream of the dam suffered higher mortality in lakes upstream of the fishway (27%) compared to fish released downstream of the dam (7%), suggesting post-passage consequences that reduce survival. Sockeye migrating through two thermally stratified lakes upstream of the dam were used as models to investigate the hypothesis that temperatures selected by sockeye salmon are related to an individual’s reproductive status and energy reserves. As predicted, I found that energy and estradiol were positively related to thermal experience. Sockeye salmon with low energy and advanced reproductive status may have selected cooler temperatures in order to reduce metabolic energy expenditure and avoid over-ripening of gametes.

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