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Butler, Natalie Ann

University of British Columbia

Pacific salmon are now experiencing temperatures in freshwater that can reach or exceed their upper thermal limits. The aims of this thesis are to evaluate the role of acclimation on the Upper Thermal Tolerance (UTL) in stream-type juvenile Chinook salmon (Oncorhynchus tshawytscha), to evaluate how different methods in measuring UTL affect the measured outcome, and determine how acclimation temperature affects post-swim mortality. Both parr and fry life stages were acclimated for two weeks at temperatures spanning present and expected future summer levels (15°C, 18°C, 20°C, 24°C). Using fish from each acclimation temperature, we measured post-swim mortality following an endurance trial (Eswim), whereby swimming fish were exposed to increasing speeds at each temperature, and subsequently returned to their initial acclimation trough and monitored for 48 hours. The effect of acclimation temperature on critical thermal maximum (CTmax) was measured by two means: stationary (CTmax stat) and swimming (CTmax swim). CTmax stat was determined by water evenly heated at 0.3°C/min in a stationary bath, with loss of equilibrium (LOE) as the indicator of CTmax stat. CTmax swim was determined using a swim flume heated at 1°C/30min with fish swimming at a fixed speed of 4 BL/s, and cessation of swimming as the endpoint. Fish acclimated to higher temperatures generally exhibited higher thermal tolerance until 24°C, where fish were not able to acclimate to higher temperatures. Based on CTmax stat trials, parr showed a consistent increase in acclimation up to 24°C, with increasing CTmax temperatures, though in CTmax swim trials, there was a distinct thermal ceiling at that temperature. Fry exhibited a greater sensitivity to increased temperatures, with a drop in CTmax at 24°C for both stationery and swimming trials. There was high post-swim mortality following the 24°C acclimation groups in the Eswim trials in both parr and fry, indicating an upper thermal limit where impaired recovery. This work highlights the need for varied metrics in studying thermal tolerance and the influence that such metrics have on the measured outcome. Warm temperatures exceeding 20°C are now routinely occurring in the study population region, so we expect increasing mortality rates of fish in coming year.

Text

2024-02-06

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/87415

Forestry

University of British Columbia

UBCV

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