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Last modified
7/14/2009 5:02:36 PM
Creation date
5/24/2009 7:15:19 AM
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UCREFRP
UCREFRP Catalog Number
9545
Author
Chart, T. E. and L. Lentsch.
Title
Flow Effects on Humpback Chub (Gila cypha) in Westwater Canyon - Final Report.
USFW Year
1999.
USFW - Doc Type
Aspinall-46,
Copyright Material
NO
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Table 10. Multinomial analysis for habitat preference by YOY Gila spp. based on actual numbers of <br />fish collected by habitat type in the Westwater Canyon sub-reach (Colorado RK 204 - <br />199.4), of Westwater Canyon, Utah. Data collected in July and August, 1992, 1994, and <br />1996 and July -Sept., 1993 and 1995. <br /> <br />HABITAT <br />TYPE <br /> <br />N= <br />Obs. % of <br />Hab. Type No. of YOY <br />chubs/ <br />habitat type Exp. # of <br />YOY chubs/ <br />habitat type <br />Chi-square <br />factor. <br />BW 28 30.1 78 440 298.2 <br />SH 37 39.8 552 582 1.57 <br />EMB 18 19.3 726 282 697.05 <br />PO 1 1.1 0 16 16.09 <br />1P 3 3.2 13 47 24.43 <br />F'T' 4 4.3 15 63 36.49 <br />SC 2 2.2 79 32 68.09 <br />Overall Chi-square =1141.89; p=0.00; df=6 <br />Overall study catch rates of 0.08 YOY chubs /meter in backwaters, 0.36 along shorelines, and <br />1.19 in the embayments indicate the greatest densities of chubs were found in the embayments as well. <br />In fact, YOY chub CPE's were greater in canyon embayments than backwaters (0.48) above the canyon. <br />The availability (surface area) of the canyon low velocity habitat types was not strongly <br />correlated with flows. Pearson correlation coefficients for the availability of canyon backwaters vs. <br />sample flow (-0.168; p=.787) and annual peak flow (0.032; p=.95) indicated little or no change over the <br />range of flows tested. Embayment habitats increased in availability with increasing sample flows (.972; <br />p=.07) and with the annual peak (.975; p=.02). A similar relationship was found when flows and habitat <br />depths were compared. This analysis incorporated only habitat data collected in August when flows <br />were relatively low and chubs were still occupying low velocity areas. The maximum depth of canyon <br />habitats (all habitats types) was positively correlated with the annual peak flow (RZ = .58; p=0.13). An <br />even stronger positive correlation was found between depth and the flows at the time of sampling (RZ = <br />.97; p=.0016). There is an apparent link between the increased surface area and resulting increased depth <br />of flooded shoreline concavities (embayments) at higher summer flows. There also appeared to be a <br />break point in this flow relationship near 6000 cfs. At higher flows, both of the primary, canyon low <br />velocity habitats (backwaters and embayments) became scarce (Figure 10). <br />Young chubs, however, did not appear to select for the deeper habitats (Table 11). Achi-square <br />analysis of presence /absence of young chubs by habitat depth indicated that chubs were not using the <br />deeper habitats (with maximum depths > 0.7 m) significantly more than was expected (p=0.38). In the <br />summer of 1996, when the highest YOY chub CPEs were recorded, habitat availability (total area of <br />backwaters and embayments combined) and maximum depth of those available habitats ranked third of <br />the five years studied. Total habitat availability and maximum depths were greatest during 1995, the <br />year of the highest spring flows and lowest YOY chub CPE. <br />12 <br />
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