9316

• UCREFRP Catalog Number: 9316
• Author: Camp Dresser & McKee Inc.
• Title: Replacement of the Plateau Creek Pipeline.
• USFW Year: 1996.
• USFW - Doc Type: Denver.
• Copyright Material: NO

backwater areas in the spring of their first year but they are difficult to find after spring
runoff, apparently because they begin using deeper habitats.
By the time the fish have reached subadult size (250 - 400 mm), they become
increasingly piscivorus. Gradually, the subadults begin moving upstream, perhaps
drawn to more suitable habitat and abundant supplies of larger food items. Over a
period of years, these fish move downstream into adult habitat many miles from the'
nursery area. Because the movement is so gradual, they become widely distributed in
the system. Male Colorado pikeminnow do not mature until about 6 years of age and
females do not mature until at least 7 years of age (USFWS 1991).
The life history of the razorback sucker has been documented in less detail, but there is
still a large body of information derived from many years of research (reviewed by
USFWS 1998). Adult razorback suckers spend most of the base flow period
(September-April) in low velocity habitats (e.g., backwaters, eddies, etc.) of the main
channel. They remain active even in cold water, but movements are local. In the
spring, when temperatures warm, photo period lengthens, and flows increase during
runoff, the adults begin spawning migrations. The fish move into off-channel staging
areas (backwaters, oxbows, flooded bottomlands) where warmer temperatures
probably facilitate the final maturation of gametes. Females remain ripe for an
extended period of time (perhaps weeks) in such areas. Responding to some stimulus,
the ripe females eventually move into the main channel where they deposit eggs in
flowing water over coarse (gravel and cobble) substrate. Hatching occurs dur9~g, or
slightly before peak runoff. Historically, larvae would have access to flooded
bottomlands and probably spent a few weeks there. When water levels receded in the
overbank areas, the larvae would have returned to the main channel. Adult razorback
suckers can survive and apparently do well as individuals in large reservoirs (e.g.,
Bradford et al. 1999), but there, as elsewhere, recruitment of young fish is virtually
nonexistent, presumably due to predation (Minckley et al. 1991, Marsh and Langhorst
1988, Pacey and Marsh 1998, Johnson and Hines 1999,)
In contrast to the Colorado pikeminnow and razorback sucker, the humpback chub was
historically restricted to only a few river reaches. This species is relatively sedentary
(i.e., not known to make extensive migrations). Its populations are now isolated from
each other due to dams and lack of intervening preferred habitat (USFWS 1990b).
Less is known about its life history requirements than in the preceding two species
accounts, especially in the UCR basin. The fish may remain in or near specific eddies
for extended periods of time. The fish spawn shortly after peak runoff with increasing
water temperatures . In the UCR basin, spawning has been recorded between mid-
June and late July when the ripe fish are captured mainly in shoreline eddies. In
general, humpback chub exhibit certain preferences for distinct geomorphic reaches
(USFWS 1990b) and also make use of various types of cover (Converse et al. 1998).
Life history information about the bonytail is scant and its habitat requirements are
virtually unknown (USFWS 1990a). Most of the information available has been
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