9406

• UCREFRP Catalog Number: 9406
• Author: Osmundson, D. B.
• Title: Importance of the '15-Mile Reach' to Colorado River Populations of Endangered Colorado Pikeminnow and Razorback Sucker.
• USFW Year: 2000.
• USFW - Doc Type: Grand Junction.
• Copyright Material: NO

is at the top of the15-mile reach (Fig. 6).
Thus, in terms of forage and suitable temper-
ature regime, the 15-mile reach may be
located in or near the most optimal part of
the Colorado River for Colorado pikemin-
now.
Low water temperature might also in-
hibit successful spawning by pikeminnow in
reaches upstream of Palisade. In De Beque
Canyon, temperatures necessary for spawn-
ing are met, but the overall thermal regime
may be less than optimal in some years. The
initiation of spawning in the Colorado River
generally occurs when river temperatures
exceed 18 ° C and spawning activity lasts 3-8
weeks (Trammell and Chart 1999). Hamman
(1981) reported that females held in race-
ways did not spawn until temperatures ex-
ceeded 20°C. In controlled experiments,
Marsh (1985) found that for eggs spawned
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Ch
20
N
L
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a? 15
L
CL 10
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and fertilized at 18 ° C, hatching success and
embryo survival was highest at 20°C.
Although some spawning occurs at cooler
temperatures (see Bestgen et al. 1998),
most spawning in the Colorado, Green, and
Yampa rivers occurs at water temperatures
between 18-22'C (McAda and Kaeding
1991, Tyus 1990, Bestgen et al. 1998,
Anderson 1999, Trammel and Chart 1999).
Analyses of temperature records at Cameo
(1986-1996) indicate that 18°C is exceeded
in both wet and dry years, but in wet years,
20'C may be only briefly attained (Fig. 7).
Thus, in some years suitable conditions for
spawning may be of short duration. In
addition, the delayed annual warming of
upstream reaches will likely delay the onset
of spawning, resulting in larvae having a
shorter first-year growing season than if
produced in more downstream reaches.
20 C Y STATE LINE
SPAWNING 18 C ---- - _?,X__ _
CAMEO
1993
MAY JUN JUL AUG SEP OCT
Month
Figure 7. Main channel temperatures (May-October) at two sites in the Colorado River during
a wet year, 1993. Measurements are from USGS gauging stations at Cameo and the
Colorado-Utah state line. Plotted daily values are the average of the daily maximum and
minimum readings. Timing and duration of temperatures in excess of 18 ° and 20 ° C (see text)
at the two sites are shown for comparison.
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