9375

• 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

Table 13. Multinomial analysis for habitat preference by YOY Gila spp. based on actual numbers of
fish collected by habitat type in the Below Canyon sub-reach (Colorado RK 185.6 - 176.0),
of Westwater Canyon, Utah. Data collected in July and August, 1992, 1994, and 1996 and
July -Sept., 1993 and 1995.

HABITAT
TYPE

N=
Obs. % of
Hab. Type No. of YOY
chubs/
habitat type Exp. # of
YOY chubs/
habitat type
Chi-square
factor.
BW 24 52.2 49 58 0.98
SH 6 13.1 44 14 G3.1
EMB 4 8.7 1 7 7.49
PO 2 4.3 8 4 2.43
IP 2 4.3 0 4 4.64
FT 7 15.2 6 20 6.59
SC 1 2.2 0 2 2.37
Overall Chi-square = 87.62; p=0.00; d,~6
However, overall study catch rates of 0.05 YOY chubs /meter in backwaters, 0.06 along
shorelines, .017 in the embayments, and 0.02 in the flooded tributary mouths indicate they were scarce
throughout. This habitat use is likely indicative of the shift in Gila species abundance from roundtail /
humpback community in the canyon upstream to a sparse, mono-specific population of roundtail chubs
in this section.
Sympatric Species
Four other native species were collected throughout the course of the study none of which were
as numerous as YOY Gila spp. In decreasing order of abundance they were: speckled dace, bluehead
sucker, flannelmouth sucker and Colorado pikeminnow (refer to Appendix Table 3). Only 12 YOY
Colorado pikeminnow were collected; six upstream of the canyon, five within Westwater Canyon, and
one below. Nursery habitat investigations on the Green and Colorado rivers (Trammel and Chart 1998a
and 1998b) revealed a YOY pikeminnow preference for scour channel backwaters in most study reaches.
Although like habitats were scarce in Westwater Canyon they were readily available both above and
below the canyon. The subject study site was likely too close to spawning areas to harbor significant
numbers of YOY pikeminnow. Catch rates of speckled dace and bluehead sucker were positively
correlated with the peak flow at the State Line gage (Table 14) as well as the cumulative flow metrics:
pre-peak flow and post-peak flow.
Nonnative cyprinids dominated the low velocity habitat collections in each of the three study
areas. Throughout the project, fathead minnows were the most numerous, followed in decreasing order
of abundance by red shiners and sand shiners. Catch rates varied among the three study areas (Figure
11). Canyon catch rates were usually lower than those upstream and downstream, with the exception of
sand shiners.
14