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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

distinguished as either the humpback form or the
roundtail form, following a qualitative and quantitative
inspection (Douglas et al. 1989; Karp and Tyus 1989).
This suggests that the morphological variation apparent
in some locations where Gila intermediates occur
(reviewed by Valdez and Clemmer 1982) may be
induced by recent habitat change. Thus, the presence of
intermediate forms in altered systems (e.g., Green River
and Colorado River) and the apparent absence of such
forms in unaltered rivers (e.g., Yampa River and Little
Colorado River) emphasizes the importance of natural
riverine environments for recovery of the humpback
chub.
Juvenile, Post Larvae, Larvae
Thirteen juvenile (168 mm-227 mm) humpback
chubs have been collected between RK 0.16 and 64 in
the Yampa Canyon by U.S. Fish and Wildlife Service
biologists (Karp and Tyus 1989). Classification of
juvenile Gila as the humpback form was based on the
same complex of morphologic characters used to
differentiate the adult life history stage (Karp and Tyus
1989). Most young humpback chubs were captured in
shoreline eddies and runs. Problems with specific
identification of small Gila in the upper Colorado River
basin have hindered the evaluation of habitat needs of
small humpback chubs. However, young-of-the-year
humpback chubs have been tentatively identified in the
lower 64 km of the Yampa Canyon (R. T. Muth and
D. E. Snyder, personal communication).
Bonytail Chub
Habitat requirements of the bonytail chub in the
Green River basin are largely unknown. Fish
collections in Echo Park (DNM) before and after
closure of Flaming Gorge Dam indicated that the
species was present in fair numbers at the confluence of
the Yampa and Green rivers (Vanicek 1967). However,
recent investigations in that area have yielded few
captures. Holden and Stalnaker (1975) reported the
capture of 36 bonytail chubs in the Yampa (lower 16 km)
and upper Green rivers between 1968 and 1970. Holden
and Crist (1981) collected one bonytail chub in the lower
Yampa River in 1979, and Service biologists captured
one suspected juvenile in 1987. Additional habitat use
information is expected from aradio-tracking study of
adult bonytail chubs introduced into the upper Green
River (DNM) in 1988 and 1989 (T. Chart, personal
communication).
Razorback Sucker
Adult
More than 500 adult razorback suckers have been
captured inflat-water sections of the upper Green River
(RK 282-552) and in the lower 21 km of the Yampa
River (Azevedo 1962; Vanicek et al. 1970; Holden and
Stalnaker 1975; Seethaler et al. 1979; McAda and
Wydoski 1980; Miller et a1.1982; Tyus et a1.1982b; Tyus
1987; U.S. Fish and Wildlife Service, unpublished data;
Fig. 5). During the nonbreeding season, adult razorback
suckers were most common in shoreline runs and
mid-channel sand bars in the mainstream Green River,
with an average water depth of < 2 m and an average
velocity of <0.5 m/s (Tyus 1987). Adult razorback
suckers overwinter in the Echo Park area of DNM
(McAda and Wydoski 1980; Valdez and Masslich 1989).
Spawning
Spawning activity of the razorback sucker has been
documented in the lower Yampa River near its
confluence with the Green River and in the upper Green
River (McAda and Wydoski 1980; Miller et al. 1982;
Tyus 1987; U.S. Fish and Wildlife Service, unpublished
data; Fig. 5). Thirty-two ripe razorback suckers
(6 females, 26 males; including 2 recaptures) were
captured on cobble and gravel bars in the lower Yampa
River in 1975,1981,1988, and 1989 at an average depth
of 0.61 m and an average velocity of 0.64 m/s (McAda
and Wydoski 1980; Miller et al. 1982; U.S. Fish and
Wildlife Service, unpublished data}.During this period,
water temperatures were variable but averaged 15°C.
The recapture of a ripe male razorback sucker in the
lower Yampa River (RK 0.16) in 1988 that had originally
been captured in the same locality in 1981 (also ripe),
indicates a fidelity to this spawning site. This fish moved
at least 52.8 km in 1988 from the upper Green River to
reach the lower Yampa River to spawn.
Spawning of razorback suckers occurred on the
ascending limb of the spring hydrograph (Fig. 14;
spawning period in 1988 delineated by a single bar
because ripe fish were collected only one day). This
pattern of razorback suckers spawning during spring
runoff was also noted in the upper Green River (Tyus
1987; U.S. Fish and Wildlife Service, unpublished data).
The capture of ripe razorback suckers in the lower
Yampa and upper Green rivers and the tentative
identification of larvae in upper Green River seine
collections (R. T. Muth and D. E. Snyder, personal
communication) indicates that razorback suckers
reproduce successfully in the upper Green River basin
(McAda and Wydoski 1980; Tyus 1987; U.S. Fish and
Wildlife Service, unpublished data). However, there is
little indication of widespread recruitment to the
juvenile stage throughout the Colorado River basin
(Holden 1978; McAda and Wydoski 1980; Minckley
1983; Tyus 1987; Marsh and Minckley 1989). Habitat
requirements of this species in riverine environments
are not well known because of the scarcity of extant
populations (Minckley 1983; Lanigan and Tyus 1989)
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