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Last modified
7/14/2009 5:02:34 PM
Creation date
5/24/2009 7:15:36 AM
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UCREFRP
UCREFRP Catalog Number
8291
Author
Chart, T. E. and L. D. Lentsch.
Title
Flow Effects on Humpback Chub (Gila Cypha) Populations in Westwater Canyon.
USFW Year
1997.
USFW - Doc Type
Aspinal-46,
Copyright Material
NO
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Westwater Carryon. . <br />In this 4.5 mile sub-reach there were only three backwaters that formed consistently and varied <br />minimally from year to year. Young of the year chubs did not select for backwaters in Westwater <br />Canyon. Due to the paucity of low velocity habitats in the canyon proper, shorelines were the <br />most commonly (44.4%) sampled habitat followed by backwaters (27.3%), embayments (17.9%) <br />and others (see Table 6 above). The backwater and embayment sampling effort was <br />representative of actual availability. Conversely, shoreline habitats were less discrete and were <br />even more abundant than the relative abundance values would suggest. The Chi square analysis <br />for presence /absence of YOY chubs by habitat type indicated that there was selection for <br />embayments, slight selection against shorelines and backwaters were utilized approximately as <br />much as,was expected (see Table 7). Overall study catch rates of 0.08 YOY chubs /meter in <br />backwaters, 0.36 along shorelines, and 1.19 in the embayments indicate the greatest densities of <br />chubs were found in the embayments as well. In fact YOY chub CPE's were greater in canyon <br />embayments than backwaters (0.48) above the canyon <br />The availability of the canyon habitat types was not strongiy correlated with flows. Pearson <br />correlation coefficients for the availability of canyon backwaters vs. sample flow (-0.168; p=.787) <br />sail annual peak flow (0.032; p=.95) indicated little or no change over the range of flows tested. <br />F.mbayment increased in availability with increasing sample flows (.972; p=.07) and with the <br />annual peak (.975; p=.02). The sample flows anc! the peak flows were linked, i.e. during the years <br />of high peak flows summer sampling flows remained high. There was never the opportunity to <br />test a late summer low flow immediately following a high spring peak Based on obsen+ation, <br />embayment habitat availability was a function of instantaneous flows or more importantly river <br />stage. These habitats are not formed as by sediment transport, but are supply a process of the <br />river inundating or stranding shoreline geology. The magnitude of the spring flood had very little <br />effect on the availability of embayments or any low velocity habitat in Westwater Canyon. The <br />few backwaters that did form in Weslwater formed in the same places from year to year. YOY <br />chubs did.use the available backwater but did not select for them. This general use of low <br />velocity areas is likely a life history strategy more common of G cypher than G robusta. <br />D_ RAFT <br />. ~ 20 <br />
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