9685

• UCREFRP Catalog Number: 9685
• Author: Tyus, H. M. and C. A. Karp.
• Title: Habitat Use and Streamflow Needs of Rare and Endangered Fishes
• USFW Year: 1989.
• USFW - Doc Type: Flaming Gorge Studies - 2nd Preliminary Draft.
• Copyright Material: NO

review) and the importance of this phenomenon needs further evaluation,
particularly in reintroduction efforts.
The capture and artificial spawning of ripe razorback suckers in the
lower Yampa and upper Green rivers (FWS unpublished data) and the tentative
identification of larvae in upper Green River seine collections (R. T. Muth
and D. Snyder, personal communication) indicates that razorback suckers
reproduce successfully in the upper Green River basin. However, there is
little indication of recruitment to the juvenile stage throughout the Colorado
River basin (Holden 1978; McAda and Wydowski 1980; Hinckley 1983; Tyus 1987;
Marsh and Hinckley 1989; Tyus and Karp, in review). Standing crops of
razorback suckers in the Green River are presumably old fish (Hinckley et al.,
in prep) and no documented recruitment has occurred since the 1960s.
The apparent lack of widespread recruitment has been attributed to
habitat alteration, such as lower water temperatures (Marsh 1985) and
predation by introduced common carp Cyprinus carpio, green sunfish, channel
catfish, flathead catfish Pylodictus olivaris, and other non-native fishes-
(Minckley 1983; Brooks et a]. 1985; Tyus 1987; Marsh and Langhorst 1988;-Marsh
and Hinckley 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 Char]ey Wash and Stewart Lake Drain should be made accessible to
razorback suckers in the spring. The introduction of young fish (reared at
Ouray National Wildlife Refuge from sex products taken from wild fish captured
on nearby Green River spawning grounds) 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 (Hinckley 1983;
Lanigan and Tyus 1989) and the absence of younger life.history stages
(McCarthy and Hinckley 1987; Tyus 1987j. Adult razorback suckers in the Green
River basin are old individuals (Tyus 1987, Hinckley et al ., in prep.) and the
low number of reproducing razorback suckers is considered limiting (Lanigan
and Tyus 1989; Tyus and Karp, in review). High spring flows, warming river
temperatures, and inundated shorelines and bottomlands are considered
essential to successful reproduction in this species.
PART III. SUMMARY AND RECOMMENDATIONS
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. Colorado squawfish, razorback sucker
and other 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.
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