Testing Temperature Preference and Critical Thermal Maximum Across Walleye Populations

Abstract

Intraspecific variation in fish, particularly temperature preference and critical thermal maximum (CTmax), can reflect the vulnerability of species to extreme warming events in the face of climate change. Using fingerling fish, we examined the temperature preferences of three Michigan walleye (Sander vitreus) populations across a latitudinal gradient using a shuttle-box arena. We then tested the CTmax of the same fish. We found no significant difference in temperature preference across the test populations; however, the CTmax of the northern population was about 0.6°C lower than one of the southern populations. We found several limitations in the use of shuttlebox experiments to reliably capture differences in thermal preferences for walleye. Additionally, we developed a new method for calculating preferred temperature which excludes periods where fish do not appear to regulate temperature. With this new method, we found an adjusted preferred temperature for Michigan walleye juveniles of 22.75 ± 2.59°C (mean±SD); this closely mirrors the reported temperature of optimal growth. The average estimated CTmax was 33.71 ± 0.43°C. Results suggest that walleye from northern populations may be more vulnerable to extreme warming events than southern populations.