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Cardiorespiratory physiology and temperature tolerance among populations of sockeye salmon (Oncorhynchus nerka)

University of British Columbia

Elevated summer water temperature has been associated with high mortality in adult sockeye salmon (Oncorhynchus nerka) during their once-in-a-lifetime migration up the Fraser River (British Columbia, Canada) to their spawning grounds. There are over 100 genetically distinct populations of sockeye salmon in the Fraser River watershed, varying in migration distance, elevation gain, river temperature and river flow. This thesis studied the physiological basis for temperature tolerance in sockeye salmon and examined the overall hypothesis that each sockeye salmon population has physiologically adapted to meet their specific upriver migration conditions. Swimming and cardiorespiratory performance were compared over a range of temperatures across six wild, migrating adult sockeye salmon populations. All populations maintained maximum performance across the entire range of temperatures typically encountered during their upriver migration, with Chilko sockeye salmon emerging as the most high temperature-tolerant. In addition, populations with more challenging migrations had greater aerobic scope, larger hearts and improved coronary supply. These results suggest that sockeye salmon populations have physiologically adapted to cope with their local upriver migration conditions, despite never before having performed the upriver migration. Temperatures exceeding the population-specific thermal optimum resulted in severely impaired aerobic scope and swimming performance. This study suggests that population-specific thermal limits are set by physiological limitations in aerobic performance. Specifically, fish may be unable to swim at warm temperature due to insufficient oxygen supply to meet demand, triggered via a cardiac limitation due to reduced scope for heart rate. Given the key role of the heart in limiting thermal tolerance, the role of cardiac adrenergic stimulation was examined as a potential mechanism underlying the observed differences in thermal tolerance across sockeye salmon populations. Chilko sockeye salmon had a greater density of ventricular β-adrenoceptors, which may provide greater cardiac capacity and protection at temperature extremes, thereby expanding their breadth of thermal tolerance compared to other populations. This thesis suggests that sockeye salmon populations will be differentially affected by warming river temperatures, raising conservation concerns for biodiversity. This work provides important insight into local adaptation in sockeye salmon and identifies a possible cause for in-river mortality associated with warm temperatures in sockeye salmon.

Text

2011-08-30

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/37013

Zoology

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/4.0/