7404

• UCREFRP Catalog Number: 7404
• Author: Masslich, W. J. and A. Wasowicz.
• Title: Interim Report - 1990 Overwinter Survival of Age-0 Colorado Squawfish in the Green and Colorado Rivers.
• USFW Year: 1990.
• USFW - Doc Type: Logan, Utah.
• Copyright Material: NO

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RESULTS
Flow and temperature ranges for the Green and Colorado Rivers during sampling periods are
presented in Table 1. Length-frequency histograms were developed for each region (Figures 1-4) to
help identify the size range of the cohort and distinguish YOY from juveniles. From these histograms
and from observations of individual fish in the field, it was decided that the maximum sizes of YOY
in fall and spring were 60 and 70 mm, respectively, for the 1987 and 1988 year classes, and 70 and
75 mm, respectively, fo`r the 1989 year class. A length of 60 mm was set as the maximum size of the
199(? year class sampled in Fall 1990.
Tables 2 and 3 present results of Fall 1990 sampling, for primary and secondary backwaters. For
subsequent analysis of overwinter survival of YOY and juvenile Colorado squawfish presented in this
report, data from primary and secondary hackwaters were pooled. Table 4 presents analysis of
sympatric species collected in the first seine haul of the primary backwater.
Reach 3 -Lower Green River
A total of 415 YOY Colorado squawfish, averaging 40 mm TL, were captured in this reach during
the fall of 1990, resulting in a catch rate of 7.7 YOY/I00 mZ (Table b). A total of 21 juvenile
squawfish, ranging from 61 to 88 mm TL were also captured (Table 7). Primary and secondary
backwaters were located in all reaches except for two; secondary backwaters could not be located in
RMI 110-105 and RMI 95-90.
The distribution of YOY Colorado squawfish in collected Reach 3 in fall and spring for the 1987,
1988 and 1989 year classes are presented in Figures 4, 5 and 6, respectively. Figure 7 shows the
distribution of the 1990 year class squawfish in Fall 1990. Results from plotting the distribution of
the 1987 year class are inconclusive due to the small size of the reach analyzed. Possible movement
of fish into the area from upstream likely created noise in the data that made interpretation of any
distribution shifts difficult to interpret. Expansion of the study reach beginning Spring 1990 allowed
for a more comprehensive view of possible shifts in distribution between fall and spring. Although
results are still inconclusive, the data suggests the possibility of downstream shift in distribution of fish
from fall to spring. Of the 12 sample reaches in the upper 60 miles of the study area, one reach
(RMI 70-75} had higher numbers in the spring. In the 12 sampling reaches of the lower half of the
study area, three reaches (RMI 15-20, 30-35 and 45-50) had higher numbers of YOY Colorado
squawfish in the spring than in fall. The effects of habitat availability on the distribution of fish will
be investigated further when aerial photography becomes available for the study reach.
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