7157

• UCREFRP Catalog Number: 7157
• Author: Haynes, C. M., et al.
• Title: Larval Colorado Squawfish ‎(
• USFW Year: 1984
• Copyright Material: YES

:JO

The Southwestern Naturalist

vol. 29, no. I

km downstream (rom the Yampa confluence) since closure of the dam.
Holden and Crist (1978) compared flow and temperature records at Jensen
for both pre- and post-impoundment periods and found that average June
through August temperatures for the period 1957-1959 were 17.8, 22.2, and
21.10C, respectively. Following dam closure, mean water temperatures for
these months were reduced i.e. 16.8,20.1, and 19.20C (1963-1966); 16.7, 19.2,
and 17.70C (1967-1977). Similarly, mean June pre-impoundment flows were
reduced from nearly 395 m3/sec (1951-1962) to approximately 195 m3/sec
(1963-1966) and 306 m3/sec (1967-1977). Squawfish reproduction had not
been documented above Jensen since 1967. Holden and Crist (1978) reported
the capture of three yearling squaw fish in 1978 at Island Park (Dinosaur
National Monument), approximately 48 km above Jensen. These fish were
apparently spawned during the drought year of 1977 when mean June flows
at Jensen were less than 50% of those for 1967-1977 and water temperatures
averaged 2IOC, i.e. 4-50 greater than the 1967-1977 mean. They concluded
that optimal water temperatures for squaw fish spawning were met in 1977.
The collection of only three yearlings suggested that, although water
temperature was appropriate for reproduction, the drought-reduced flow of
the Yampa was not sufficient to substantially augment the regulated flow of
the Green, thereby reducing spawning and/or increasing egg or larval
mortality.
Other evidence tends to corroborate the contention that the reproductive
cycle of Colorado squawfish is regulated by water temperature. Hamman
(1981) obtained spawning at 180C only by induction with carp pituitary
injections, whereas spawning occurred spontaneously at 20-2IOC. Beames-
derfer and Bjornn (1980) observed that peak spawning of the closely related
Northern squawfish (P. oregonensis) in Idaho was correlated with water
temperatures of 1O-130C and that spawning ceased at 16-180C. A reduction
in spawning was also observed following a storm-induced temperature
decline of about 50.
Our observations would appear to support the hypothesis that spawning
in Colorado squawfish is correlated with the occurence of receding water
levels and rising water temperatures (Vanicek and Kramer, 1969; Seethaler,
1978; Holden, 1979, 1980). It appears likely that high spring flows serve
importantly for flushing spawning substrate and flooding shoreline embay-
ments which would serve as rearing areas, while spawning is induced by
rapidly rising water temperatures. Other exogenous factors, such as photope-
riod, water clarity, water quality, etc. may also exert a regulatory role in
this species, but they have not been investigated. For example, as De
Vlaming (1972) stressed, w~ter temperature and photoperiod effects are not
readily separable in cyprinids since few studies have adequately controlled
these variables experimentally. Additionally, more than 40 agricultural
chemicals were applied in the Colorado River watershed above Grand
Junction in 1980 (R. Valdez, pers. comm.); however, the possible longterm
sublethal effects of these compounds on squawfish reproduction and larval
survivorship have not been studied. Further, lordosis has been observed in
1981 Colorado River squawfish YOY (Haynes, unpublished) and in
roundtail chub (Gila robusta) YOY in both the Colorado and Yampa rivers