Date Approved
8-19-2026
Graduate Degree Type
Thesis
Degree Name
Biology (M.S.)
Degree Program
Biology
First Advisor
Mark Luttenton
Second Advisor
Carl Ruetz III
Third Advisor
Eric Snyder
Academic Year
2025/2026
Abstract
Climate change threatens the persistence and resilience of coldwater ectotherms. Stream- dwelling salmonids such as the Brown Trout (Salmo trutta) have a narrow thermal tolerance that influences growth, survival, and distribution. Trout can mitigate thermal stress by migrating to a source of thermal refuge and behaviorally thermoregulating. I used radio telemetry with temperature-sensitive transmitters to observe movement patterns, habitat selection, and thermoregulatory behavior of Brown Trout during July and August in the North Branch of the Au Sable River (NBAR), a groundwater-dominated stream in Northern Michigan, USA. I tracked 15 Brown Trout from July 1 to August 19, 2025 while the environmental variables of temperature, light, and water depth were logged concurrently by passive sensors. Contrary to expectations, Brown Trout exhibited limited evidence of population-wide thermoregulation despite the availability of thermal refuge throughout the study segments and area. Most individuals maintained body temperatures similar to ambient stream temperature, and only one individual consistently occupied thermal refuge. Stream temperature was not associated with the probability of movement from the homesite, whereas stream depth and light significantly influenced movement. Environmental variables did not explain movement distance, and most of the variation was attributed to the individual fish. These findings suggest Brown Trout do not consistently use thermal refuge to avoid physiologically stressful temperatures or maintain body temperatures beneficial to growth. Instead, widespread use of thermal refuge may occur only during extreme thermal events with sustained elevated temperatures.
ScholarWorks Citation
Clark, Logan D., "Thermal Refuge Use and Movement of Brown Trout in the North Branch Au Sable River, Michigan, USA" (2026). Masters Theses. 1198.
https://scholarworks.gvsu.edu/theses/1198
