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Expansion of the American white pelican Pelicanus erythrorhynchoscolony on Blackfoot Reservoir, Idaho, and the associated declines in adfluvial Yellowstone Cutthroat Trout Oncorhynchus clarkii bouvieriin the upper Blackfoot River drainage has generated concern about the impact of pelican predation on this native trout stock. During a 4-year study, 4,653 wild Yellowstone Cutthroat Trout were tagged using a combination of radiotelemetry and PIT tags. Annual predation rate estimates were made by recovering Yellowstone Cutthroat Trout tags from the nesting islands of American white pelicans. On-island tag recovery rates were corrected for ingested tags that went undetected during island searches and for tags that were deposited away from the nesting islands. American white pelicans consumed tagged Yellowstone Cutthroat Trout ranging from 150 mm to 580 mm TL and showed no size selection within that range for their prey. Predation rates on adult and juvenile Yellowstone Cutthroat Trout generally exceeded 20%, and the highest values were above 60%. Our independent methods (telemetry and PIT tagging) for estimating pelican predation on adult Yellowstone Cutthroat Trout produced similar results. Annual river flow conditions varied markedly and may have contributed to some of the observed range in predation rate estimates. Predation by the pelican colony appears to be a likely contributor to the recent collapse of Yellowstone Cutthroat Trout in the upper Blackfoot River drainage. In the past, overexploitation by anglers severely reduced the trout population and was remedied by implementing catch-and-release regulations. The current predation impact poses a greater management challenge, namely, finding a balanced approach for conserving both the native trout stock and the pelican colony. Received April 29, 2014; accepted February 5, 2015

AbstractExpansion of the American white pelican Pelicanus erythrorhynchoscolony on Blackfoot Reservoir, Idaho, and the associated declines in adfluvial Yellowstone Cutthroat Trout Oncorhynchus clarkii bouvieriin the upper Blackfoot River drainage has generated concern about the impact of pelican predation on this native trout stock. During a 4-year study, 4,653 wild Yellowstone Cutthroat Trout were tagged using a combination of radiotelemetry and PIT tags. Annual predation rate estimates were made by recovering Yellowstone Cutthroat Trout tags from the nesting islands of American white pelicans. On-island tag recovery rates were corrected for ingested tags that went undetected during island searches and for tags that were deposited away from the nesting islands. American white pelicans consumed tagged Yellowstone Cutthroat Trout ranging from 150 mm to 580 mm TL and showed no size selection within that range for their prey. Predation rates on adult and juvenile Yellowstone Cutthroat Trout generally exceeded 20%, and the highest values were above 60%. Our independent methods (telemetry and PIT tagging) for estimating pelican predation on adult Yellowstone Cutthroat Trout produced similar results. Annual river flow conditions varied markedly and may have contributed to some of the observed range in predation rate estimates. Predation by the pelican colony appears to be a likely contributor to the recent collapse of Yellowstone Cutthroat Trout in the upper Blackfoot River drainage. In the past, overexploitation by anglers severely reduced the trout population and was remedied by implementing catch-and-release regulations. The current predation impact poses a greater management challenge, namely, finding a balanced approach for conserving both the native trout stock and the pelican colony.Received April 29, 2014; accepted February 5, 2015

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.