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Last modified
7/14/2009 5:02:36 PM
Creation date
6/1/2009 12:40:11 PM
Metadata
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UCREFRP
UCREFRP Catalog Number
9531
Author
Hudson, J. M. and J. A. Jackson.
Title
Populaiton Estimates for Humpback Chub (Gila cypha) and Roundtail Chub (gila robusta) in Westwater Canyon, Colorado River, Utah, 1998-2000.
USFW Year
2003.
USFW - Doc Type
Salt Lake City.
Copyright Material
NO
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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 />
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