7735

• UCREFRP Catalog Number: 7735
• Author: Bates, B., T. Chart and M. Moretti.
• Title: Colorado Squawfish Interagency Standardized Monitoring Program, Utah, 1986-90, Lower Green and Colorado Rivers.
• USFW Year: 1993.
• USFW - Doc Type: Publication Number 93-11,
• Copyright Material: NO

10

In an attempt to better understand the relationship between
habitat temperature and concentrations of YOY, the resultant CPUE
of each seine haul was plotted against the appropriate
temperature gradient (Figures 8 & 9). Temperature gradient
refers to difference between habitat and main channel
temperature. Linear regression analyses revealed only a weak
positive correlation between the variables on the Green
(r=0.028) and Colorado (r=0.36) Rivers.

Catch per unit effort was also compared to temperature data
to determine if YOY squawfish were selecting backwaters based on
temperature (Appendix III). No relationship was found using the
wilcoxxon Matched Pairs test (P > 0.05).

The results of these analyses seem to indicate that
temperature may not be the major habitat component that young
squawfish are keying in on in the fall.

By the time the YOY fish community is sampled each Fall, age
0+ squawfish appear to be randomly distributed throughout the
lower 120 miles of the Green River (Figure 10). Squawfish
distribution on the lower Colorado was less uniform (Figure 11).
From 1986-1900 the overwhelming majority (89.6%) of YOY squawfish
were collected from Colorado RM 65 downstream to the confluence.
Interestingly 1986, the highest flow year on the Colorado, was
the only year squawfish were found upstream of RM 65 in
appreciable numbers. ~

Hydrographs for the 2 rivers from 1986 to 1990 were examined
to determine differences that may have led to changes in mean
catch rate and mean total length (Appendix IV). Flows were
higher and of greater duration, with lower temperatures in 1986.
Spawning dates and growing seasons for YOY squawfish were
estimated using criterion developed by Nessler et al (1987) and
McCada and Kaeding (1989), which indicates that spawning occurs
during an increase in flows after peak flows during the
descending portion of the hydrograph, and when the water
temperature is near 20oC.

Growth of YOY squawfish stops when water temperature drops
below 13oC, (Tables 3 & 4.) (Thompson 1989). Spawning was
apparently later in 1986, and temperatures dropped below those
conducive to optimal growth earlier.

Growth rates for YOY Colorado squawfish were similar on the
rivers. Mean total length was lowest basinwide in 1986, and
highest in 1988 on the Colorado and 1990 on the Green. (Figures
12 & 13). Multiple regressions to estimate YOY total length in

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