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Last modified
7/14/2009 5:02:35 PM
Creation date
5/20/2009 10:52:25 AM
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UCREFRP
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
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CPEs are circled to call attention to what the researchers recall as good catches of humpback chub. In <br />July, 1994, the humpback catch was high at all sites particularly when compared to the coincidental <br />roundtail catch. In July of 1996, catch of humpbacks was not especially high throughout the canyon, but <br />more notable was the poor catch of roundtails. The catch rate and recapture data do not suggest an influx <br />of humpbacks to Westwater Canyon, while the same data does not clearly indicate an exodus of roundtail <br />chub. Humpback chub may have been more active locally during this postrunoff /post spawning period <br />making them more susceptible to our sampling techniques. Conversely, the roundtail may have been <br />more sedentary. <br />The roundtail chub catch rates also fluctuated greatly from trip to trip with a project high of 1.26 <br />fish per hour recorded at the Cougar Bar in October, 1992, and the project low, 0.07, recorded at the <br />same site in April of the same year (Figure 16). Project means by site were: RK 198.6 = .53; RK 194.4 = <br />.44; and RK 192 = .5288. A regression of CPEs against sampling date indicated a strong negative trend _ <br />in roundtail catch at all sites: RK 198.6 (RZ = -.64; p=.045); RK 194.4 (RZ = -.63; p=.07); and RK 192 (RZ <br />_ -.74; p=.013). <br />Sympatric Species <br />Channel catfish were the most abundant Sympatric species in main channel habitats (trammel net <br />catch). However, at 14.3% of the total catch, they were much less abundant than native chubs (refer to <br />Fig. 14). Native suckers (flannelmouth = 3.2 % and bluehead = 7.2%) were the next most abundant <br />species followed by common carp which only comprised 2.3% of the trammel net catch. Despite the <br />abundance of native chubs, only ten Colorado pikeminnow were collected in the nets throughout the <br />study accounting for 0.4% of the total. Incidental collections of white sucker, brown trout and several <br />centrarchids, individually comprising less than 1 % of the catch, completed the catch list. <br />In the shoreline sampling (electrofishing and hoop netting), the catch was more diverse (refer to <br />Fig. 13). Again, native chubs in the aggregate accounted for the majority of the catch, however common <br />carp were the next most abundant species accounting for 8.5% of the electrofishing catch. Native <br />suckers were better represented than in the trammel nets and more abundant than channel catfish. <br />Largemouth bass (n=9) that were not collected in trammel nets were collected electrofishing. <br />PIT Tagging <br />Late juvenile (> 175 mm TL) and adult sized chubs were PIT tagged throughout the study in an <br />effort to compare the species movements, determine growth, and provide mark-recapture information for <br />population estimation. It also provided a method to validate species identification and sex determination. <br />A total of 837 humpback chub and 1070 roundtail chubs were tagged throughout this study (Appendix <br />Tables 5 and 6). Fifty-seven humpback chub (6.8% of the total) were recaptured; three of these were <br />recaptured a second time and one fish three times (Appendix Table 7). Seventy-one roundtail chubs <br />(6.6% of the total tagged) were recaptured; four of those were recaptured a second time, one was <br />recaptured on three occasions, and one roundtail was recaptured four times (Appendix Table 8). The <br />average time elapsed between captures was 574.6 days for humpback chub and 447.8 days for roundtails. <br />Species Identification and Sex Ratio <br />Three of five chubs not initially identified to species were, upon recapture, identified as <br />humpback chub; the remaining two as roundtails. Chubs are more difficult to identify to species at <br />smaller sizes. No humpbacks were ever reclassified as roundtails and vice versa, an affirmation of the <br />distinctive morphology of Gila spp. in Westwater Canyon. Although three trips were conducted in July <br />(1992, 1994, and 1996) fewer than five individuals per trip were tuberculated or expressing reproductive <br />products -virtually all were in post-spawn condition (or immature). Based on the back calculated <br />17 <br />
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