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<br />Roundtail Chub <br />1 Population Estimates <br />The model selection function of Program CAPTURE resulted in variability among years in <br />determination of the most appropriate estimator for the roundtail chub capture-recapture data <br />(Appendix II). The jackknife estimator (Mh) ranked highest in 1998 and 2000 (0.85 and 0.88, <br />~ respectively). However, this estimator was inappropriate for the data in 1999 (0.00). The Darroch <br />estimator (Mt) ranked highest in 1999 (1.00). However, this estimator was not appropriate for the <br />data in 1998 or 2000 (0.05 and 0.00, respectively). Considering these results and to allow a better <br />comparison with the population estimate of humpback chub in Westwater Canyon, the null <br />estimator (Mo) was used to determine the population estimates of adult roundtail chub in Westwater <br />~ Canyon, 1998-2000. <br />The adult roundtail chub population estimate was 5,005 individuals in 1998 (Table 3). The profile <br />likelihood interval around this estimate was 3,586 - 19,781 (CV = 0.30; p-hat = 0.026). In 1999, the <br />adult roundtail chub population estimate decreased to 4,234 individuals (Table 3). The profile <br />. likelihood interval around this estimate was 3,349 -12,917 (CV = 0.23) with a slightly higher <br />probability of capture (p-hat = 0.037). The adult roundtail chub population estimate in 2000 <br />increased to approximately the 1998 abundance at 4,971 individuals (Table 3). The probability of <br />capture also decreased at the same time (p-hat = 0.031), while the profile likelihood interval was <br />slightly tighter (3,824 - 16,641; CV = 0.25). The relationship among these three estimates indicates <br />short-term stability in the Westwater Canyon adult roundtail chub population (Figure 7). <br />r <br />CPUE <br />Total trammel net captures for roundtail were 397 in 1998, 481 in 1999, and 521 in 2000 (Table 2). <br />Total captures in 1998 included 389 adults, seven of which were recaptured. One additional subadult <br />~ roundtail chub was captured in the trammel nets. In 1999, 457 adults were included in the total <br />captures. Twelve of these individuals were recaptured. Subadult captures in the trammel nets <br />increased to twelve individuals. The total captures for 2000 included 458 adult roundtail chub. Ten <br />of these were recaptured. Subadult captures included in total trammel net captures for 2000 were a <br />project high of 53 individuals. <br /> <br />Mean catch per unit effort (CPUE) slightly decreased across all passes from 1998 to 2000 (Figure <br />8). The slope of this decreasing trend does not significantly depart from zero. Contrary to this <br />decreasing trend, CPUE appeared to increase among passes within years. The Kruskal-Wallis test <br />supported this observation indicating significant differences (p < 0.05) between passes within and <br />. among years, except for 2000. The Kolmogorov-Smirnov test indicated there were significant <br />differences (p < 0.05) in the distribution of catch rates between passes within and among all years. <br />Comparisons of mean CPUE and the distribution of catch rates between years (all passes combined) <br />indicated significant differences (p < 0.05) between all years except for mean CPUE between 1999 <br />and 2000. <br />S <br />~ 7 <br />