Potential Loss of Thermal Habitat for Brook Trout, Due to Climatic Warming, in Two Southern Ontario Streams

Abstract

I calibrated a hydrometeorological model of stream temperature to two southern Ontario streams in the summer to estimate potential reductions, due to climatic warming, of thermal habitat for brook trout Salvelinus fontinalis. Summer habitat for brook trout in both streams, determined from electrofishing surveys during 1987 and 1988, was delimited downstream by a thermal barrier of about 24°C. Tagging data for one stream suggested that brook trout moved upstream to summer habitat as water temperatures in downstream areas increased during spring and summer. To estimate upstream movement of the thermal habitat barriers and concomitant reductions in summer habitat for brook trout due to climatic warming, I forced the calibrated stream models with the changes in mean July and August air temperatures (increase, 4.1°C) projected for the region by the climate warming scenario of the Goddard Institute for Space Studies. I also adjusted the temperature of groundwater discharging to the streams by the projected change in mean annual air temperature (increase, 4.8°C). Elevated air and groundwater temperatures increased maximum summer stream temperatures and moved the thermal habitat barriers upstream, which reduced summer thermal habitat for brook trout in the two streams by 42 and 30%.