Influence of Variable Interannual Summer Water Temperatures on Brook Trout Growth, Consumption, Reproduction, and Mortality in an Unstratified Adirondack Lake

Abstract Stressful water temperatures negatively affect physiological processes in fishes, yet evidence for how elevated temperatures influence population-level characteristics is rare. An 8-year field study of brook trout Salvelinus fontinalis in an unstratified Adirondack lake revealed that an aggregate measure of chronically stressful summer water temperatures strongly influenced brook trout population-level characteristics. We quantified chronic thermal stress using the cumulative degree-days over which bottom temperatures exceeded a range of thresholds (18–22°C) and found that the strongest relationships were with cumulative degree-days over 20°C (DD>20). Across years with similar brook trout densities, warmer summer water temperatures resulted in decreased brook trout growth, but growth was not reduced in a year with high water temperatures and low density. Maximum stomach fullness was negatively related to water temperature. Reproductive activity was negatively correlated with stressful summer ther...