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sizeable portion of the catch, particularly when compared with catch rates in Desolation Canyon <br />where catfish dominate main channel and shoreline catches. The habitats available in Westwater <br />Canyon, partiarlarly during high flows, appear to keep the resident channel catfish population in <br />check. This is likely key to the success of the native chubs in Westwater Canyon as well as Black <br />Rocks. . <br />PIT Tagging <br />Late juvenile (> 175mm 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 <br />information for population estimation. It also provided a method to validate species identificaxion <br />and sex determination. A total of 837 humpback chub and 1070 roundtail chubs were tagged <br />throughout this study (Appendix Tables 5 and 6). Fifty-seven humpback chub (6.8% of the <br />total) were recaptured; three of these were recaptured a second time and one fish three times <br />(Appendix Table 'n. Seventy -one roundtail chubs (6.6% of the total tagged) were recaptured; <br />four of those were recaptured a second time, one was recaptured on three occasions, and one <br />roundtail was recaptured four tunes (Appendix Table 8). The average time elapsed between <br />captures was 574.6 days for humpback chub and 447.8 days for roundtails. <br />Speceis Identification and Sex Ratio <br />Three of five chubs not initially identified to species were, upon recapture, identified as humpback <br />chub; the remaining two as roundtails. Chubs are more difficult to identify to species at smaller <br />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 <br />in July (1992, 1994, and 1996) fewer than five individuals per trip were tuberculated or <br />expressing~reproductive products -virtually all were in post-spawn condition (or immature). <br />Based on the back calculated hatching dates (see above) sampling occurred closest to the spawn <br />in 1996, but even that trip was several weeks subsequent to the calculated spawning peak. <br />DRAFT <br />38 <br />