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UBC Theses and Dissertations

Maximum heart rate as a means of rapidly estimating optimal temperature for aerobic scope in salmon : its potential for application Casselman, Matthew Thomas


Knowing the optimal temperature (Topt) for aerobic scope of fishes may be useful for predicting responses to warming environmental temperature because Topt is when fish can allocate the most oxygen to activity. However, the broad application of Topt measurements is hampered by the time required to determine Topt of a species. This thesis sought to develop a rapid method of estimating Topt of Pacific salmon species (genus Oncorhynchus) based on evidence that suggests the decline in aerobic scope above Topt is triggered by a limitation on maximum heart rate (fH). Thus, maximum fH at elevated temperature is thought to limit oxygen convection through the circulatory system, and hence limits both maximum metabolic rate and aerobic scope. Measurements of metabolic rate and fH were taken over a range of temperatures at rest and following exhaustive exercise in juvenile coho salmon (O. kisutch) to confirm the association between Topt and maximum fH. In vivo measurements revealed a maximum fH limitation at the Topt for aerobic scope, supporting the use of fH to estimate Topt. The potential for expediting measurements of maximum fH during acute warming was investigated using anaesthetized coho salmon and pharmacological stimulation of fH. In coho salmon sedated with low doses of anaesthetic, pharmacologically stimulated fH was equivalent to the maximum fH measured in vivo. Breakpoint analysis of the relationship between maximum fH and temperature demonstrated a limitation on maximum fH that corresponded closely with the Topt for aerobic scope. Further, while Topt measurements took three weeks to complete, maximum fH measurements were completed in three days. Therefore, the novel maximum fH technique considerably reduced the time needed to estimate Topt and may be broadly suited to estimating Topt both within and outside of the Oncorhynchus genus. Potential application of this rapid Topt estimation method is discussed in relation to temperature data collected from two local coho salmon-bearing streams. Temperature data also allowed for the examination of stream warming and cooling dynamics and identification of habitat critical to buffering anthropogenic disturbances to stream temperature. These data highlight the importance of riparian areas for maintaining the thermal integrity of waterways.

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