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• UCREFRP Catalog Number: 7300
• Author: Tyus, H. M. and C. A. Karp.
• Title: Habitat Use and Streamflow Needs of Rare and Endangered Fishes, Yampa River, Colorado.
• USFW Year: 1989.
• USFW - Doc Type: Biological Report 89‎(14)‎,
• Copyright Material: NO

by a reduction in spring runoff. A gradual decrease in
summer flows, following spring scouring, with a
concomitant decrease in sediment load, aids in
preventing siltation of cobble bars. Thus, timing and
duration of flushing flows must be evaluated as potential
limiting factors for successful reproduction by Colorado
squawfish.
Reproductive success of Colorado squawfish is
believed to be limited by the low number of spawning
adults. Captures of adult Colorado squawfish with lures
and bait in the Yampa River (Saile 1986; U.S. Fish and
Wildlife Service, unpublished data) suggest that large
individuals are susceptible to angling pressure. Service
records (Vernal, Utah) show that in some years up to
10% of the tagged Colorado squawtish are captured by
anglers. Martinez (1986) also noted several instances of
incidental captures in the White River. Thus,
protection of adult Colorado squawfish should be
encouraged because of the small number of juveniles,
the long time required to attain maturity (> 5 years), and
the susceptibility of large individuals to angling and
other incidental captures.
Competition with introduced fishes for food or space
and predation by nonnative forms are two factors that
potentially limit survival of adult Colorado squawfish in
the Yampa River. Capture of northern pike (Esox
Ittcitts) and channel catfish in habitats shared by adult
Colorado squawfish (Wick et al. 1985; U.S. Fish and
Wildlife Service, unpublished data) suggests that these
nonnative predators may be competing with or preying
on Colorado squawfish. Also, although Pimental et al.
(1985) found that Colorado squawfish did not prefer
channel catfish as prey, observations of channel catfish
lodged in throats of adult Colorado squawfish (McAda
1983; Pimental et a1.1985; Wick et a1.1985) indicate that
these introduced fish may adversely affect survival of
Colorado squawfish.
Flow fluctuations in winter have the potential for
disturbing preferred winter habitats, and the resultant
movement patterns suggest that such disruptions may
stress Colorado squawfish (Wick and Hawkins 1989).
Thus, significant fluctuations in water surface level in
winter are undesirable.
Larvae and Postlarvae
Factors potentially limiting the distribution and abun-
dance of young Colorado squawGsh in the Yampa River
include the alteration of natural flow and temperature
patterns and alteration of natural sediment and nutrient
loads. Such alterations may negatively affect availability
(quality and quantity) of critical nursery habitat in the
Green River. In addition, proliferation of nonnative com-
petitors and predators is considered limiting.
Mortality of drifting larvae is directly related to flow,
river temperature, availability of backwater habitat, and
predator load. Young Colorado squawfish are routinely
collected in isolated pools in the Green River system
(U.S. Fish and Wildlife Service, unpublished data).
These pools form when decreasing flows strand water
from the main channel. Natural fluctuations in river level
usually make this a gradual process and allow entrapped
fish an escape route. However, abrupt fluctuations in
river level, as is characteristic of some regulated systems,
could increase mortality of small fishes by cutting off
escape routes and thereby increasing potential for
competitive interactions and exposure to terrestrial
predation. Herons (Ardeidae), raccoons (Procyon
lotor), garter snakes (Thantttopltis sp.), and other
animals have been observed feeding on fishes trapped
in isolated pools (Erman and Leidy 1975; U.S. Fish and
Wildlife Service, unpublished dataj.
Effects of competition and predation by introduced
fishes on growth and survival of young Colorado
squawfish has yet to be adequately assessed, but the
common use of backwater habitats and foods by young
Colorado squawfish and other small introduced fish
species (Jacobi and Jacobi 1982; McAda and Tyus 1984;
U.S. Fish and Wildlife Service, unpublished data)
indicates the potential for significant interspecific
interaction. Karp and Tyus (in press) suggest that
growth and survival of young Colorado squawfish may
be adversely affected by introduced green sunfish
(Lepomis cyanellus), red shiner (Notropis lutrensis), and
fathead minnow (Pintepltales prontelas), particularly
when increases or decreases in river level reduce the
availability of quality backwater habitat.
There is some indication that abundance of
nonnative fishes may be decreased by periods of high
flows, whereas native species seem to be little affected
(Haynes and Muth 1984; Minckley and Meffe 1987; T.
Nesler, written communication). These preliminary
relations support the hypothesis that native fishes
exhibit greater tolerance to fluctuating flow regimens.
Late summer and fall are critical periods for growth
and survival of young Colorado squawcsh, and flows in
the Green River system at this time are historically and
predictably low. Tyus et al. (1987) noted that abundance
and growth of young Colorado squawfish in the Green
River was negatively correlated with late summer and
fall flows (r = -0.73, P < 0.06 for abundance; r = -0.88,
P < 0.01 for growth). During late summer and fall, catch
and growth were highest in 1979 and 1980, when
discharge ranged from 45.28 to 53.77 m3/s at Jensen,
Utah, and lowest in 1983 and 1984, when discharge
ranged from 84.9 to 118.86 m3/s (Tyus et al. 1987). In
1983 and 1984, unusually high releases from Flaming
Gorge Dam in late summer and fall inundated
backwater nursery areas, and survivorship of young
Colorado squawf-sh was low. These relations suggest
that flows optimizing growth and survival of small
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