7055

• UCREFRP Catalog Number: 7055
• Author: Archer, D. L., L. R. Kaeding and B. D. Burdick.
• Title: A Study of the Endangered Fishes of the Upper Colorado River.
• USFW Year: 1985.
• USFW - Doc Type: Grand Junction, Colorado.
• Copyright Material: NO

I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I

Larval Colorado sQuawfish

Larval sampling was conducted between Palisade and the confluence with
the Green River from July through August in 1982, and from July through
October in 1983 and 1984. A total of 148 larval Colorado squawfish was
collected in 1982, 41 in 1983, and 48 in 1984. Larval Colorado squawfish
occurred in 14' of the collections in 1982, 6' in 1983, and 9' in 1984
(Appendix Tables 28-30). Significantly more larval Colorado squawfish were
collected from reaches 2 and 3 during 1982 than during 1983 or 1984 (Reach 2,
p=.Ol [Appendix Table 31]). The upper reach (Reach 4) also contained more
larval Colorado squawfish in 1982 than in 1983 or 1984, but this difference was
not significant. Larval Colorado squawfish were first collected in mid July in
1982 and 1984, but they were not found until the second week of August in 1983
(Figure 3). Because of earlier warming of the river and the effect of
temperature on spawning, larval Colorado squawfish were collected from
downstream areas before they were found in upstream areas within years. Reaches
2 and 3 contained the largest numbers of larval Colorado squawfish during all
three 'years of the study; however, this difference was significant only in 1982
(p=.05). Some larval Colorado squawfish were collected from upper Lake Powell
during 1982 and 1984; however, frequency of sampling there was irregular and
comparisons of resulting data among years or between this and other study
reaches are therefore difficult.

Estimated earliest spawning periods in the lower reaches were early July,
1982, and late July, 1983 and 1984; spawning continued through August and
early September in all years (Table 5). Spawning began in the Grand Valley
(Reach 4) in mid July, 1982 and 1984, and in mid August, 1983. Estimated peak
spawning activity there occurred in early August, 1982 and in late August,
1983 and 1984. In the upper reach, spawning activity was generally associated
with an accumulation of about 500 degree days> 12 C. Estimated peak spawning
in 1982 and 1983 and the beginning of spawning in 1983 and 1984 occurred
within 80 degree days of 500 (Table 6, Figure 4). Spawning in 1982 occurred
when maximum temperatures neared 20 C in the upper reach. However, in 1983
and 1984 spawning occurred after maximum-daily temperatures had been near or
above 20 C for almost one month. Spawning began in 1982 and 1983 when
strea~lows at the Colorado-Utah border were about 9,000 to 12,000 cfs (255 to
3~6 m Isec), and spawning peaked at flows of 5,000 to 9,000 cfs (140 to 255
m Isec (Table 6, Figure 5).3 However, spawning occurred at discharges of 10,000
to 21,000 cfs (280 to 588 m /sec) in 1984 (Table 6, Figure 5).

Post-larval. aQe-O Colorado sQuawfish

One river-wide, systematic collection of post-larval, age-O Colorado
squawfish was made in 1982 (Sept), two in 1983 (Sept and Aug), and three in
1984 (Aug, Sept and Oct). Reach 1 (lake Powell) was not sampled. A total of
56 Colorado squawfish was collected in 1982, 159 in 1983, and 78 in 1984
(Table 7, Figures 6-8, Appendix Tables 32-34). The middle study reaches (2
and 3) contained the largest number of post-larval, age-O Colorado squawfish
during all years. In 1982 and 1984, reach 2 (RM 0-65) contained the highest
concentration of these small fish (p=.OI in 1982 [Appendix Table 35]), whereas
reach 3 (RM 60-110) contained the most fish in 1983 (p=.OI). Post-larval,
age-Q Colorado squawfish were collected in the Grand Valley area for the first
time in 1983 and were again collected there in 1984. They might have been
absent from our samples from this reach in 1982 because they passed through

16