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the recaptured young Colorado pikeminnow were within the same 5-mile section where they were <br />originally marked. <br />Overwinter movement (between autumn and spring sampling) was about 3 miles or less. <br />Young Colorado pikeminnow apparently make local movements on a diel basis in response to <br />environmental conditions. <br />We were unable to draw conclusions about whether typical winter flow operations at Flaming <br />Gorge Dam affected overwinter survival of young-of-year Colorado pikeminnow. Survival could <br />not be estimated because population estimates of the fall and the following spring were too <br />imprecise and the level of winter flow fluctuations may have been too low to affect survival. <br />Ice jams were observed in the Ouray Backwater Complex that resulted in stage changes up to <br />0.75-1.50 m and transformed backwaters into flow-through environments. <br />Prior to ice formation, seining was the most efficient method for catching age-0 Colorado <br />pikeminnow. All gear types including baiting traps and using neon lights were ineffective in <br />capturing young Colorado pikeminnow under ice. The most effective technique for under ice <br />sampling was an underwater camera and video cassette recorder. Diurnal, nocturnal, and <br />crepuscular fish activity were observed, and total number were counted over a 6 to 8 h time <br />frame. <br />Movement Rates under Simulated Winter Conditions <br />The temperature-dependent response of fish movement in the absence of disturbance <br />(spontaneous) was best approximated by an exponential model with the form y = 0.0895eo.1532t <br />where y is body lengths/s (bVs) and t is temperature (°C). <br />Activity declines exponentially with temperature, but young Colorado pikeminnow remain active <br />during winter, even when water temperatures approached 0°C. <br />xix