9375

• UCREFRP Catalog Number: 9375
• Author: Kimball, J. F.
• Title: Flow Effects on Humpback Chub ‎(Gila cypha)‎ in Westwater Canyon.
• USFW Year: 1999.
• USFW - Doc Type: Salt Lake City.
• Copyright Material: NO

Table 16. Growth of three size classes of humpback and roundtail chub recaptured in Westwater
Canyon, Colorado River; 1992-1996. Time elapsed between capture is not factored in
average growth values.
Humpback Chub
Length Group n Average TL (mm) Average Growth (mm)
175 - 225 13 210 18.7
226 - 250 19 239 16.2
> 250 30 283 8.67
Roundtail Chub
Length Group n Average TL (mm) Average Growth (mm)
175 - 225 29 205 46.6
226 - 250 18 237.8 15.6
> 250 31 277.5 12.6
Growth of the humpbacks slows earlier than that of the roundtail chubs. Roundtails tagged
between 175 and 225 mm TL grew on average an additional 46.6 mm, whereas humpbacks of similar
size at the time of capture only grew 18.7 mm. Taking into account the greater average time between
capture for humpback chub we presume they persist /survive longer in Westwater Canyon than do
roundtails.
Population Estimates
Recapture rates were too low to run estimates through the closed population models available in
the CAPTURE program. Sequential (year to year) Lincoln-Peterson estimates were run to get a feel for
population size. Obviously, based on the varying capture probabilities, the estimates vary as indicated by
the confidence intervals (Table 17).
There was one instance where a humpback chub population estimate exceeded its CI: the 1996
estimate of 1050 humpbacks at Cougar Bar (RK 194.4). However, there were some trends in CPE that
were reflected in these population estimates: the Hades population was the smallest, the upward trend at
the Miner's Cabin site (RK 198.6) and the slight downward trend at Hades Bar (RK 192). The roundtail
chub population at Miner's Cabin was estimated at 1760 in 1993 and declined to 721 in the final year of
study, which follows the trend in CPE discussed earlier. The population of roundtails at Cougar Bar was
estimated at 1210 in 1993. A similar population size was estimated at the Hades Bar site in 1992, where
population estimates were generally less than the sites upstream and declined in the latter portion of the
study as did the CPE's.
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