Coping with a Warm Environment: Behavioral Thermoregulation by Lake Trout

Temperature-sensing ultrasonic transmitters were used to monitor the behavior of eight individual lake trout Salvelinus namaycush in two lakes: a shallow lake that becomes isothermal (15–20°C) during late summer and a typical dimictic lake with a cold hypolimnion. Use of a cool, nearshore groundwater discharge site, a behavior never before documented for lake trout, was observed among some fish in the shallow lake when ambient lake temperatures exceeded the speciesˈ preferred thermal range of 6–13°C. We suggest that during very warm years, groundwater refugia may be important habitat for lake trout and that these refugia should be protected.