9305

• UCREFRP Catalog Number: 9305
• Author: U.S. Fish and Wildlife Service.
• Title: Final Biological Opinion for the Operation of Flaming Gorge Dam.
• USFW Year: 1992.
• USFW - Doc Type: Denver, CO.
• Copyright Material: NO

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In Dinosaur, humpback chub spawn in spring and early summer following highest
spring flows at river temperatures about 20 °C (Karp and Tyus 1990a). This
included May and June in low (e.g., 1987 and 1989) and average (e.g., 1988
flow years but extended into July during the 198b high-flow year. Ripe fish
are predominantly captured in shoreline eddy ha~;itats in,-the upper 30 miles of
Yampa Canyon, and there is some indication that these fish remain in or near
specific eddies for extended periods and return to the safe eddy during the
spawning season in different years (Karp and Tyus 1990a). It is unknown where
humpback chubs deposit eggs, but the use of shoreline eddies that are
associated with boulder/sand substrates is considered important to the
breeding requirements of humpback chub in Dinosaur. 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. Loss or reduction of spring runoff could reduce availability of
spawning habitat and consequently adversely affect humpback chub reproduction.
Habitat alternation also may promote hybridization with other species (Valdez
and Clemmer 1982). Flow reductions (absence of spring peak) and decreased
temperatures were implicated as factors curtailing successful spawn and
increasing competition in the Colorado River (Kaeding and Zimmerman 1983).
Larval and Juvenile
Larval and young-of-year humpback chub are generally found in low velocity
microhabitats associated with backwaters and eddies. Fish grow from 7.5-
10.5 cm during their first year of life, and by age-2 many are 200 mm
(8 inches). Males begin reaching sexual maturity at age-2 and females at
age-3. Once humpback chubs reach sexual maturity growth slows considerably.
BONYTAIL CHUB
Status and Distribution
Historically, the bonytail chub occurred throughout the Colorado River main
stem and its major tributaries, including the Gila and Salt Rivers in the
lower basin and the Green, Yampa, White, Gunnison, and San Juan Rivers in the
upper basin. Recent collections indicate the fish is extremely rare and is
extirpated from much of its former range, although individual fish are still
occasionally collected from the upper and lower basins. Supplemental stocking
from hatchery fish and maintaining stocks in hatcheries may be necessary to
preclude this species from becoming extinct. The recovery goal for bonytail
chub (U.S. Fish and Wildlife Service 1990b) is to "prevent immediate
extinction."
Adults
Habitat requirements of the bonytail chub in the Green River basin are little
known. Fish collections in Echo Park (Dinosaur) before and after closure of
Flaming Gorge Dam indicated that the species was present in moderate numbers
at the confluence of Yampa and Green Rivers (Vanicek 1967). But, more recent
investigations in that area yielded few captures. Holden and Stalnaker (1975)
reported the capture of 36 bonytail chubs in Yampa (lower 10 miles) and upper
Green Rivers from 1968 to 1910. Holden and Crist (1981) collected one