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

During spring and early summer, humpback chub are most prevalent in
high-gradient, whitewater reaches dominated by rocky runs, riffles and rapids.
Adult fish are most often collected in seasonally flooded shoreline eddies
that are downstream of large boulders and upstream of rapids. Juveniles appear
to be more common in smaller eddies in rocky shoreline runs. Humpback chub
remain rare in DNM, only 133 juvenile and adult fish were captured during
spring sampling efforts from 1986-1989 (Karp and Tyus 1990a). Feeding habits
of humpback chub are relatively unknown in the Green River basin, but stomachs
of a few fish contained hymenopterans and plant debris. Humpback chub also
feed on Mormon crickets and presumably other foods at various levels within
the water column (Karp and Tyus 1990a). The paucity of humpback chub in
canyons of the upper Green River may be linked with a reduction in the number
of invertebrate taxa (noted by Pearson 1967) following construction of
Flaming Gorge Dam.
Although fall and winter habitat requirements of humpback chub are not
well known, some observations in DNM suggest that the fish remain in pools
and eddies of impounded water and rapids in low flow conditions (Karp and
Tyus 1990a). Minimum flows required to maintain such habitats from mid-summer
through late winter have not yet been determined.
In DNM, humpback chub spawn in spring and early summer following highest
spring flows at river temperatures about 20o C (Figure 7; Karp and Tyus
1990a). This included May and June in low- (e.g., 1987, 1989) and average-
(e.g., 1988) flow years but extended into July during the 1986 high-flow
year. Ripe fish are predominantly captured in shoreline eddy habitats in the
upper 48 km of Yampa Canyon and there is some indication that these fish
remain in or near specific eddies for extended periods and return to the same
eddy during the spawning season in different years (Karp and Tyus 1990a}. It
is unknown where humpback chub deposit eggs, but we consider the use of
shoreline eddies associated with boulder/sand substrates important to the
breeding requirements of humpback chub in DNM. Availability of shoreline eddy
habitat is greatest with spring flooding and decreases thereafter with
decreasing summer flows; these habitats are formed and maintained by spring
runoff in DNM. Loss or reduction of spring runoff could reduce availability of
spawning habitat and consequently adversely affect humpback chub reproduction.
Habitat alteration may also promote hybridization with other species (Valdez
and Clemmer 1982). Flow reductions and decreased temperatures have been
implicated as factors curtailing successful spawn and increasing competition
in the Colorado River (Kaeding and Zimmerman 1983).
In DNM, adult humpback chub were captured in association with 19 other
fishes, but were most commonly captured with roundtail chub and the
introduced channel catfish when angling. The high number of channel catfish in
habitats used by mature humpback chub (35% angling catch, Karp and Tyus
1990a), in addition to their potential ability to compete with and prey on
humpback chub and their omnivorous feeding behavior (Kaeding and Zimmerman
1983; Tyus and Nikirk 1990; Karp and Tyus 1990a; C. 0. Minckley, personal
communication), suggests that channel catfish may adversely affect survival of
humpback chub in DNM. Channel catfish may avoid periods of low flow in
tributary streams and they may be using mainstream habitats in the Green River
for winter refugia as in some other river systems (Newcomb 1989). Flows
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