8211

• UCREFRP Catalog Number: 8211
• Author: U.S. Bureau of Reclamation and Fish and Wildlife Service.
• Title: Final Environmental Assessment
• USFW Year: 1997.
• USFW - Doc Type: Providing Fish Passage at the Grand Valley Irrigation Company diversion Dam on the Colorado River.
• Copyright Material: NO

APPENDIX A
BACKGROUND MATERIAL ON THE ENDANGERED FISHES
The two endangered fish species considered in this EA, the Colorado squawfish and razorback
sucker, are known to be highly or moderately migratory (Tyus and McAda 1984; Tyus 1987;
Tyus 1990; Tyus 1991). The construction of dams in the Upper Colorado River Basin present
barriers to the natural migration tendencies of these two fishes (Burdick and Kaeding 1990; U.S.
Bureau of Reclamation and U.S. Fish and Wildlife Service 1995).
The Colorado squawfish can be termed a highly migratory species while the razorback sucker is a
moderately migratory species, based on tagging studies (Tyus 1985, 1986; Tyus and Karp 1990;
Mickey et al. 1993; Wick et al. 1982). Movement and use of habitat varies by life stage (age) for
both species and various habitats appear to be important to survival in their life history. Recovery
of the fish involves the development of self-sustaining populations through natural reproduction;
therefore, recovery efforts must consider all aspects of the life history and habitat requirements if
development of self-sustaining populations is to be realized.
Presently, the Colorado squawfish is absent from its historic range in the river from the Price-
Stubb Dam upstream to Rifle, and razorback suckers are extremely rare upstream from Palisade.
Colorado squawfish larvae (when fish emerge from eggs, they are termed larvae) drift
downstream from spawning areas, perhaps over 90 miles or more and this may serve as a way to
disperse young into suitable backwater areas (Haynes et al. 1984; Nesler et al. 1988; Tyus and
Haines 1991). As the larvae grow to a larger size, they move upstream to establish a "home area"
used for feeding and resting during most of the year (Tyus 1991). Adult squawfish exhibit a high
fidelity to return to specific spawning sites but migrate back to a "home area" for feeding after
spawning (Tyus 1985, 1990; Tyus and McAda 1984).
Larval squawfish drift downstream from spawning areas and occupy warm, shallow, backwaters
as they become larger (Tyus 1991). Small juveniles remain in backwater areas and larger
juveniles or subadults move upstream to occupy the mainstem and major tributaries as feeding and
resting areas that may be a long distance from spawning sites (Tyus and Karp 1989). The
squawfish is considered a "large river" fish that inhabits the mainstem of the Colorado and Green
Rivers and major tributaries such as the Gunnison, White and Yampa Rivers. Young-of-the-year
and juveniles were generally captured in backwaters that were 3 feet or less in depth over silt or
sand substrates, with low water velocities (Twedt and Holden 1980). Haynes et al. (1984)
reported that young squawfish occupy areas where water velocity is less than 0.1 feet per second.
Adult squawfish occupied;habitats with sand, gravel, or cobble substrates with water velocities of
0.08 to 0.39 feet per second'(Twedt and Holden 1980). Adults occupy pool and eddy habitats
along the river shoreline with a medium depth (3 to 6 feet) during pre- and post-runoff periods.
During periods of high flow, adults prefer backwater areas and the flooded mouths of tributaries.
Spawning fish use specific cobble bars in runs to deposit their eggs but return to resting-staging-
feeding areas in pools and eddies in other parts of the basin (Tyus 1990).
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