1108

• UCREFRP Catalog Number: 1108
• Author: Valdez, R. A.
• Title: Fisheries Biology And Rafting Annual Summary Report - 1987
• USFW Year: 1988.
• USFW - Doc Type: ‎(Contract no. 6-CS-40-03980)‎.
• Copyright Material: NO

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Summary of Endangered Fish Captured

Colorado Squawfish

A total of 1016 Colorado squawfish were captured during the eight trips through
Cataract Canyon. Included were 2 adults, 69 juveniles (Table 19), 834 YOY, and
111 larvae (Table 20). All of the adults and juveniles were returned alive, as
well as all YOY that could be field identified. The remainder of the YOY and
all of the larvae were preserved and sent to the Larval Fish Laboratory for
identification. Of the 2235 specimens identified by the LFL, 279 were larvae
or YOY Colorado squawfish (Appendix C). The following is a breakdown by age
category of the squawfish handled and associated information.

Adults. Table 19 summarizes all of the adult (400 mm+ TL) Colorado squawfish
handled during the 1987 Cataract Canyon study. Only two adults were captured;
one in April at RM 16.2, near Indian Creek; and one in July at the confluence,
RM 216.3. Although sampling conditions were good during most of the eight
trips, no other adult squawfish were seen or captured. Four adults were
captured in 1985, and 5 were captured in 1986.

Juveniles. A total of 69 juvenile Colorado squawfish were handled during this
investigation. A list of these fish and associated information is presented in
Table 20. Although the usual length range for juveniles is 60-400 rom TL, some
of the juveniles (immature fish greater than one calendar year of age) were in
the 40 and 50 rom size range. The relatively small size for the 1986 year class
may be explained by their relatively late hatching dates. A further explana-
tion of this phenomenon is presented in the following section.

Young-Of-The-Year and Larvae. A total of 834 YOY and 111 larval (<60 rom TL)
Colorado squawfish were handled during this investigation. The YOY were
defined as those fish past their larval stage of development and less than one
calendar year of age. The larval fish are defined as described by Snyder
(1985). A list of the YOYand larvae with associated information are presented
in Table 20. To minimize mortality to these fish from handling, only some were
measured in the field. These lengths, along with those provided by the Larval
Fi sh Lab (LFL), from specimens sent for identification, are included in
Appendix B. The reports of the LFL are also included in Appendix C of this
report.

i. Distribution. The distribution of YOY squawfish is examined in the
Cataract Canyon study area for 1985, 1986, and 1987. Since the distribution of
these fish was not uniform and appeared to be influenced by habitat and the
geographical nature of the river, the area was stratified into four regions
(Figure 2): (1) Green River from Mineral Bottom to the confluence, RM 50.0-
0.0; (2) Colorado River from the confluence to the first rapid in Cataract, RM
216.5 - 212.5; (3) Colorado River in Cataract Canyon, RM 212.5 - 201.5; and
(4) Lake powell inflow from above Ten Cent Rapid to Palmer Canyon, RM 201.5-
195.0. In all three years examined, numbers of YOY captured by seining,
percentage of total catch, and CPE was highest in region 1, followed by regions
2, 3, and 4, in that order. CPE of YOY squawfish in region 1 in all three
years exceeds the minimum of 0.9 fish/lOm2, established to designate high-

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