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<br />Several factors contributed to within year variability of CPUE, among them differing discharges, <br /> <br />water clarity, and crew skills. <br /> <br />Simulation showed that CPUE, measured at a precision characterized by a CV = 0.31, <br /> <br />was unlikely to detect the kinds of trends needed for monitoring humpback chub populations <br /> <br /> <br />(Figure 6). When CPUE was annually decreased by 1 %, after 20 years of annual monitoring <br /> <br />(18% decrease CPUE), a significant decline was detected 18% of the time. When CPUE was <br /> <br /> <br />annually decreased by 5%, after 10 years (40% decline in CPUE), a significant decline was <br /> <br />detected 37% of the time. And when the CPUE was annually decreased by 10%, after 10 years <br /> <br /> <br />(65% decline in CPUE), a significant decline was detected 79% of the time. <br /> <br />Discussion <br /> <br />Adult captures. Electrofishing and, to a lesser extent, angling were effective for capturing <br /> <br /> <br />adult humpback chub in Yampa Canyon. We captured 86 (83 different fish and 3 recaptures) <br /> <br /> <br />adult humpback chub> 150 mm TL in 1998-2000, primarily by electrofishing with rafts at a rate <br /> <br /> <br />of 0.80 fish per hour and by angling at a catch rate of 0.04 fish per hour. An earlier study <br /> <br /> <br />conducted by the Colorado River Fish Project in 1987-1989 captured 130 humpback chub <br /> <br /> <br />mostly by electrofishing at a rate of 1.03 perhour and angling at 0.65 per hour (Karp and Tyus <br /> <br /> <br />] 990). Because of uncertainties of how electro fishing hours were defined in the 1987-1989 <br /> <br />study and different anglers involved in the two studies, we are hesitant to compare catch rates for <br /> <br />information about population trend. <br /> <br />Although we did not observe any electrofishing mortality or other harmful effects, others <br /> <br />12 <br />