7047

• UCREFRP Catalog Number: 7047
• Author: Tyus, H. M. and C. A. Karp.
• Title: Habitat Use and Streamflow Needs of Rare and Endangered Fishes in the Green River, Utah
• USFW Year: 1991.
• USFW - Doc Type: Final Report.
• Copyright Material: NO

suckers in the Green River are presumably old fish (Minckiey et al., in prep)
and no recruitment has been documented since the 1960s.
The apparent lack of widespread recruitment in razorback sucker has been
attributed to habitat alteration, such as lower water temperatures (Marsh
1985) and predation by introduced common carp Cyprinus car io, green sunfish,
channel catfish, flathead catfish Pvlodictus olivaris, and other non-native
fishes (Minckiey 1983; Brooks et al. 1985; Tyus 1987; Marsh and Langhorst
1988; Marsh and Minckiey 1989). Predation by non-native fishes is believed a
serious threat to the survival and recovery efforts of razorback sucker. The
absence of young fish in the Green River basin population may also be linked
with the reduced availability of inundated shorelines due to curtailment of
spring flooding following closure of Flaming Gorge Dam. Naturally inundated
lowlands such as Old Charley Wash and Stewart Lake Drain that were previously
accessible to razorback suckers in the spring are now not accessible due to
blockage and low water levels. The introduction of young fish (reared at Ouray
National Wildlife Refuge from gametes taken from wild fish) may ultimately
result in natural recruitment if the number of spawning adults, and
consequently the number of young fish, is increased.
Habitat requirements of this species in riverine environments are not
well known because of the scarcity of extant populations (Minckiey 1983;
Lanigan and Tyus 1989) and the absence of younger life history stages
(McCarthy and Minckiey 1987; Tyus 1987). Adult razorback suckers in the Green
River basin are old individuals (Tyus 1987; Minckiey et al., in prep.) and the
low number of reproducing razorback suckers is considered limiting (Lanigan
and Tyus 1989; Tyus and Karp 1990). We consider lower winter flows, high
spring flows, warming river temperatures, and inundated shorelines and
bottomlands as factors influencing the survival, successful reproduction, and
recruitment of this species.
SUMMARY
General
The Green River basin is an important riverine system for the maintenance
and recovery of the endangered Colorado River fishes. Flows of the tributary
Yampa River are singularly important for maintaining a spring peak on the
Green River hydrograph (Figure 3), thereby mitigating some of the adverse
effects of flow regulation by Flaming Gorge Dam on the native fish fauna.
Flows of the Yampa River, particularly spring runoff, may also enhance usable
fish habitat by inhibiting the invasion and proliferation of introduced fishes
that evolved in more mesic environments (Tyus and Karp 1989). Colorado
squawfish, razorback sucker and other native fishes depend on habitats in the
Yampa and Green rivers for fulfillment of various life history requirements,
and thus, the two rivers must be viewed as a single system when determining
flow needs.
The Green River basin supports the largest numbers of Colorado squawfish
(Tyus 1990) and razorback suckers (Lanigan and Tyus 1989) in native riverine
habitats. The humpback chub is presumed self-sustaining in DNM, but low
numbers make its status precarious (Karp and Tyus 1990a). The persistence of
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