Physiological Metrics Effectively Assess Thermal Stress and Habitat Quality of Redband Trout

Thermal habitat degradation is a substantial concern in salmon-bearing streams, particularly in eastern Oregon.  We have developed a method that can rapidly, effectively, and non-lethally monitor thermal habitat quality by evaluating the physiological status of individual fish.  We tested this method during summer of 2009 in the John Day River (JDR; summer water temperatures >25°C), compared results to the Crooked River (CR; temperatures ~10°C), and performed a comparable laboratory study to isolate the effects of temperature.  In the latter, 3 tanks per treatment were raised to either 25°C or 23°C for 25 days, then returned to 13°C for 55 days, with 3 tanks held at 13°C (control) during the 80 day experiment.  For both studies we examined the effects of thermal stress by looking at changes in body size, heat shock protein 70 (hsp70), and ability to accumulate whole body lipids (WBLs). In the laboratory fish were fed 2% body per day, while prey consumption was examined in fish from JDR and CR.  For both field and laboratory studies, fish were weighed and measured, livers and fin clips were analyzed by for hsp70 using Western blot analysis, WBLs measured by proximate analysis, and stomach contents removed, identified, weighed, and ash free dry mass (AFDM) was determined.   Levels of hsp70 increased in liver and fin clips from JDR fish, indicative of thermal stress, and they did not increase length or weight. No thermal response was observed in CR fish, which did increase in size over the study period.  These results were echoed in laboratory studies; fish at 23°C and 25°C had elevated hsp70 up to 25 d following thermal stress exposure, and thermally stressed fish grew less than controls.  Likewise, fish WBLs increased over the course of the summer only in the coolest streams (CR) and in the coolest experimental tank(s), or in field fish that were able to increase food consumption.   Overall, we conclude that fish in warm waters likely use energy for hsp70 production and not growth under extreme heat stress, while fish from the cooler waters (e.g. CR) are less thermally stressed, have greater WBLs, and are better able to grow than those in warm streams (JDR).  Laboratory study results support this conclusion.  Overall, our work shows that measures of hsp70 and WBLs provide simple metrics to evaluate thermal habitat quality, and can serve as indicators of restoration success in thermally impacted systems.