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WESTWATER CANYON:.1992-1994 <br /> ,REL. CHUB COHORT STRENGTH <br />0 <br />5 25 <br /> „ <br />. <br />. ~~„~ <br />~ <br /> <br />~ 0.4 . as.s.~ n; <br />..._. ._____._._. ~ _.........._._.._.---___.___. ____.._. <br />20 .... <br />r <br />~- m <br />N 0.3 - __~._..---_.... ._..._. 15 LL <br />~ -- <br />v <br /> <br />2 <br />0 <br /> <br />10 W <br />a <br />N ~ <br />. - - --- <br /> <br />O <br />~ ~ n; <br />Dane <br />a~f <br />~ ~ <br />W <br />a 0.1 <br />5 W <br />a <br /> <br />~ 0 <br /> 1992 1993 1994 <br /> <br /> <br />Figure 9. Relative abundance of three cohorts (1992, 1993, and 1994) of chubs collected in <br />Westwater Canyon, Colorado River, 1992.1996. Age 0 CPE reads off the primary Y-axis and <br />represents catch from the dates indicated as-well as the size of the YOY at that time; data is from <br />the canyon sub-reach only. Age 1+ and 2+ read off the secondary y-axis and represents a mean <br />catch of the two fish community trips that year -all sites combined. <br />:, <br />Relative abundance of the 1992, 1993, and 1994 cohorts is graphically presented in Figure 9. <br />Obvioulsy, AgeO and Ageland 2 CPEs are not comparable (seine catch vs electrofsihing). <br />Therefore the ifrtention is to compare the relative abundance of similar age groups between <br />cohorts. Catch rates of the 1992 and 1993 cohort increased through time (Age 1 to Age 2) <br />which suggests either, c~ differential sampling eff ciency (larger fish are more susceptible to <br />electrofishing) and / or b. immigration of juvenile chubs into the study area.- The 1995 cohort, <br />as discussed in the YOY catch analysis, was simply non-eadstent, which was substantiated in the <br />1996 electrofishing sampling (refer to Appendix Table 4) . If chubs were produced in stronger <br />numbers either upstream or downstream of the studied areas in 1995, canyon immigration did not <br />occur. Survival of the 1996 cohort, the strongest of the five YOY cohorts studied, was beyond <br />the scope of the present study. .~ <br />DRAFT <br />25 <br />