Temperature-Related Changes in Habitat Quality and Use by Bonneville Cutthroat Trout in Regulated and Unregulated River Segments

Abstract

The availability of suitable habitat is often viewed as one of most important limiting factors for animal populations. In this study, we examined the composition and spatial distribution of stream habitat based on summer water temperature using airborne thermal imagery, floating temperature surveys, and fixed temperature data loggers in a regulated and unregulated segment of the Bear River in Idaho and Wyoming. We also used temperature-sensitive radio telemetry tags to measure water temperature in habitats used by Bonneville cutthroat trout Oncorhynchus clarkii utah. We found that when available water temperatures increased in the Bear River, cutthroat trout in the regulated segment continuously selected cooler habitats that followed a similar rate of increase as available water temperatures. In the unregulated segment, cutthroat trout did not select significantly cooler available water temperatures when measured over the entire study period. However, cutthroat trout in the unregulated segment did select cooler water temperatures during the peak period of high water temperatures in July. In the regulated river segment, patches of habitat with hospitable water temperatures were small, infrequent, and widely distributed. Whereas, in the unregulated river segment, habitat patches with hospitable water temperatures were larger, more frequent, and in closer proximity to one another. Our data indicate that during the peak of summer temperatures the availability of habitat below the thermal maxima of cutthroat trout becomes very limited, but they are able to locate and use these small patches of habitat during the warmest part of the summer.