7225

• UCREFRP Catalog Number: 7225
• Author: Kaeding, L. R., D. B. Osmundson and C. R. Berry.
• Title: Temperature as a Resource Limiting Colorado Squawfish in the Upper Colorado River Basin.
• USFW Year: 1985.
• USFW - Doc Type: \
• Copyright Material: YES

Wyoming
N "
Yampa
~i
Q. White
0 100 200
~ A
Kilometers ~ Colorado
~
Utah
Gunnison
Nevada
et
J
Cp~o
Q;~
rado
San Juan
B
New Mexico
Arizona
California
C
Gila River
Mexico
Figure 1. Map of the Colorado Hiver basin showing rivers that historically"
provided habitat for Colorado sgauwfish (light lines) and those
that presently contain Colorado squawfish (heavy lines). (Modified
from Seethaler 1978.) Sites of temperature-data collection in
upper (A), middle (ii) and lower (C) river reaches are indicated.
Seethaler (1978) examined the gonads of 147 upper-basin Colorado
squawfish 184--652 mm long and concluded that the onset of sexual maturity
occurred about 428 mm TL (6 years of age) (Figure 2). Spawning of Colorado
squawfish in the upper basin normally begins in July or August, when water
temperatures reach 20-22 C. This conclusion is based on probable spawning
activity of radiot"egged adult. Colorado squawfish (Tyus and McAda 1984), on the
subsequent occurrence of larvae (Haynes et al. 1984), and on observations on
the spawning activity of captive adults (Hammon 1981). Additional information
on the life history of Colorado squawfish was provided by Seethaler (197$) and
Holden and Wick (1982).
The Colorado squawfish of the upper basin is relatively slow--growing and
late-maturing--life-history characteristics unusual to be those of a principal
piscavore. Normally, successful predators grow rapidly (to better use prey
148
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