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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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Catch rates above the canyon were greatest during the summer of 1993 and 1996; average to <br />above average water years. Catch rates within Westwater Canyon were less variable throughout the <br />study indicating spawning success within the canyon (i.e. humpback chub spawning success) may be less <br />dependent on the magnitude of the spring flows. Based on these five years of data, there appeared to be <br />little correlation between spawning success as measured by YOY captures and river flows, however <br />some relationships with other environmental variables were evident (Table 5). <br />Table 5. Pearson Correlation coefficients /associated probabilities for YOY chub CPEs vs a variety <br />of flow and temperature parameters (see Table 1 for descriptions). Catch rates are from two <br />sub-reaches (above and within Westwater Canyon) during the months of July and August, <br />1992 -1996. <br />FLO{YPARAMETERS ABOVE _ JUI..Y ABOVE -AUG CANY -JULY CANY -AUG <br />STPK -.53 / .47 .38 / .52 -.56 ! .32 -.06 / .91 <br />STPKPRE .98 / .016 .14 / .82 .97 / .004 .72 / .17 <br />CISPK -.56 / .43 .41 / .49 -.587 / .30 -.10 / .87 <br />PRPKFLO -.56 / .43 .15 / /81 -.57 / .31 -.18 / .77 <br />POSPKFLO -.45 / .54 .45 / .45 -.49 / .40 -.OS / .93 <br />PREPKIO .22 / .77 -.71 / .17 .22 / .72 -.25 / .67 <br />POSPK20 .73 / .27 .04 / .94 .75 / .14 .19 / .7G <br />CISMAYDEV -.681 / .383 -.004 / .99 -.17 / .78 -.58 / .31 <br />CIS.TUNDE V .25 / .74 -.96 / .008 .07 / .90 -.47 / .42 <br />Very few significant correlations were found. There was a strong positive correlation found <br />between July YOY chub catch rates (both above and within the canyon) and previous years' <br />instantaneous peak runoff. By August, the effect of the previous year's flows had apparently <br />diminished, but still explained a considerable portion of the variability in canyon catch rates (RZ=.72). <br />The other significant correlation resulted when YOY chub catch rates upstream of Westwater Canyon <br />were regressed against the absolute amount the observed June monthly mean deviated from the historic <br />mean (24,000 cfs). In other words, the closer the observed June monthly mean flows were to the <br />historic June monthly mean flow the greater our catch of YOY chubs in August, above the canyon. <br />Similar, but not significant, relationships were found when comparing the August canyon catch rates, and <br />when looking at a similar flow analysis incorporating May monthly averages. <br />The simple relationship between flow and chub reproductive success, as indexed by catch rate, <br />does not appear to be linear (Figure 8). In this graphical representation, it appears that on average chub <br />reproductive success was maximized when the Colorado River peaks near 30,000 cfs as they did in 1996. <br />Flows much less than this and flows much greater are likely outside the optimum flow window. <br />YOY chub habitat <br />Low velocity habitats in the three sampling strata were sampled under a variety of flows. The <br />majority (48.3%) of YOY sampling trips (Appendix Table 3) occurred when the Colorado river was <br />8 <br />
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