Ecological significance of movement patterns of Bonneville cutthroat trout in a western Wyoming watershed (Oncorhynchus clarki utah)

I studied the seasonal movement patterns of Bonneville cutthroat trout, Oncorhynchus clarki utah, in the Thomas Fork drainage of western Wyoming and eastern Idaho. My objectives were to determine if high water temperature affected movement patterns, the complexity of cutthroat trout movement patterns could be simplified into distinct groups, movement varied across season, movement was related to growth differences throughout the drainage, and movement patterns differed between males and females. Although water temperatures in some tributaries exceeded lethal limits for Bonneville cutthroat trout, fish did not emigrate from these tributaries. It appears that the large diel water temperature cycle in these tributaries provided enough recovery time at night to allow fish to survive despite spending a few hours each day above lethal water temperatures. I determined that fish could not be divided into discrete groups of mobile and sedentary individuals, rather movement was a continuum, based on movement patterns of fish after spawning. Post-spawning movements ranged from 0.5 to 82 km, and larger fish moved farther than smaller fish. Movement did not seem to be related to growth rates, which were similar in the tributaries and the mainstem. Fish movement during spring was extensive, but no movements greater than 0.5 km occurred during the summer. Variation in movement across seasons supported the idea that fish populations cannot be categorized into mobile and sedentary components. There was no difference in movement patterns based on sex. Cutthroat trout in the Thomas Fork tolerate extreme conditions during the summer and move over a continuum of distances downstream throughout the watershed in the spring but remain relatively stationary throughout the summer. Given the range of movements of this population, fragmentation by irrigation diversions is probably detrimental. Maintaining or re-establishing drainage connectivity will be a critical component to conserving cutthroat trout in this and other watersheds.