8185

• UCREFRP Catalog Number: 8185
• Author: Valdez, R. A. and B. R. Cowdell.
• Title: Annual Summary Report-1992\
• USFW Year: 1993.
• Copyright Material: NO

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3.2.3 1991 Year Class

A total of 525 age-O Colorado squawfish were captured in this reach in fall 1991, resulting in a CPE of
3.71/100 m2. Catch rate dropped 67% to 1.20/100 m2 in spring 1992. Total number of squawfish captured
dropped by 65%, from 525 to 184.

3.3 REACH 1 . THE LOWER COLORADO RNER

Reach 1 on the Colorado River extends from Fish Ford (RM 106) to the confluence of the Green and
Colorado Rivers (RM 0). Data presented here for Reach 1 includes only the lower 50 miles, above the
confluence. Backwater habitats, sampled in this reach since 1987 averaged 2.3 ft deep. Temperatures during
fall were typically 2.10C warmer than the mainchannel, and backwaters in spring were 2.80C warmer than the
mainchanneL Analyses of overwinter survival for Reach 1, including catch rates of sympatric species and catch
rates and numbers of Colorado squawfish were performed by the Service, Grand Junction CRFP Field Station.
A brief summary of CPE's and total numbers are presented here for purposes of comparison.

3.3.1 1987 Year Class

A total of 31 age-O Colorado squawfish were captured in the lower 50 miles of this reach in fall 1987 (Table
6), while only 8 were captured in spring 1988. CPE in fall was 1.24/100 m2, compared to 0.45/100 m2 in
spring. CPE and total numbers decreased by 64% and 74%, respectively.

Fish captured in fall averaged 44 mm TL, while those captured in spring, about 6 months later, averaged 57
mm TL. Average growth of age-O squawfish during the 6-month winter period was 13 mm; most of the growth
probably occurred during October, 1987, which remained a relatively warm and mild month. Average length
of age-O squawfish in this reach was greater than in Reach 3 of the Green River in both fall (34 mm TL) and
spring (43 mm TL). Fish from the Green River were usually larger in both fall and spring (Personal
communications with Miles Moretti, UDWR, April 1987), because water temperatures were generally higher
than in the Colorado River.

Two juveniles were captured in this reach in fall 1987, and one was captured in spring 1988 (Table 7). No
CPE statistics were computed considering the small numbers of fish involved. Juveniles caught in fall ranged
from 71 to 112 mm TL, while the fish captured in spring was 80 mm TL.

3.3.2 1988 Year Class

Total numbers and CPE of the 1988 year class showed increases over the winter. From fall 1988 to spring
1989, total numbers increased from 89 to 186, and CPE increased from 2.64 to 4.92/100 m2. This magnitude
of increase can be explained by immigration of age-O from upstream regions as indicated by changes in CPE
for lO-mile sections (Figure A-14; Courtesy of C. McAda, U.S. Fish and Wildlife Service, Grand Junction,
CO). Average change in length for these fish from fall to spring was from 42 to 45 mm TL

As in the Green River, several seine hauls were taken along the shoreline, off the mouths of backwaters to
determine if any numbers of age-O Colorado squawflsh were occupying other habitats. No squawtish were
found in such efforts. It was noted that the Colorado River was slightly warmer than the Green River, and
that backwaters sampled were 1 to goC warmer than the main channel.

The number of juvenile Colorado squawtish was also high in the Colorado River, as previously discussed for
the Green River. The numbers decreased from 36 to 2.4 juveniles from fall 1988 to spring 1989. These fish
ranged in length from 61 to 99 mm TL in fall and from 71 to 116 mm TL in spring, and were all considered
from the 1987 year class.

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