UBC Theses and Dissertations
The cumulative effects of physiology, temperature, and natal water cues on the migration behaviour and survival of adult sockeye salmon during passage through the Seton River hydroelectric system, British Columbia Middleton, Collin Thomas
Upriver migrating adult Pacific salmon home to natal sites following natal water cues while also undergoing a suite of physiological changes to prepare for spawning. Migrants can encounter myriad environmental conditions that are physiologically and energetically challenging throughout these journeys. Many freshwater migration corridors have also been converted into hydroelectric systems (hydrosystems) that can change the composition of flows such that the availability and concentration of natal water cues can vary substantially. How such flow composition changes affect migration behaviour has rarely been examined, while the cumulative effects of environmental and physiological factors on the fate of migrating adult salmon in regulated rivers are not well understood. Using the Seton hydrosystem in British Columbia and two populations of sockeye salmon as a model, I conducted a field radio-tagging study that examined how physiology, temperature, and natal water concentration affected the behaviour and fate of adult salmon migrating through a regulated river while enroute to natal spawning sites. Most tagged migrants (89%) delayed in the outlet of the Seton powerhouse that discharges strong concentrations of natal water, and subsequently wandered in the mainstem Fraser River before continuing their upstream migration into the Seton River, where natal water cues can also vary. I found few associations between physiological stress and reproductive hormone levels with powerhouse delays and wandering, although fish with higher energy content were generally slower migrating through the whole hydrosystem. Higher temperatures and elevated natal water concentrations were associated with shorter delays at the powerhouse and less wandering, but only among late-run migrants. I found little evidence that the cumulative effects of physiology and environmental conditions during hydrosystem passage were related to survival to natal sites, suggesting that other factors aside from those encountered during hydrosystem passage (e.g. environmental factors prior to reaching the hydrosystem) may have played a role in influencing survival post dam-passage. My thesis provides the first detailed account of how varying natal water concentrations affects the homing behaviour of wild migrating adult salmon and how the cumulative effects of physiology and environmental conditions experienced during passage through a regulated migration corridor influences survival to natal sites.
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