7202

• UCREFRP Catalog Number: 7202
• Author: Osmundson, D. B. and L. R. Kaeding.
• Title: Studies of Colorado Squawfish and Razorback Sucker Use of the '15-Mile Reach' of the Upper Colorado River as Part of Conservation Measures for the Green Mountain and Ruedi Reservoir Water Sales
• USFW Year: 1989.
• USFW - Doc Type: Final Report.
• Copyright Material: NO

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INTRODUCTION

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The range of the Colorado squawfish (Ptychocheilus Lucius) and razorback
sucker (Xyrauchen texanus) has been reduced by about 75% since the turn of
the century (Seethaler 1978, McAda and Wydoski 1980). Although both fish
are rare in their remaining habitat, only the Colorado squawfish is feder-
ally listed as 'endangered', despite the fact that the razorback is con-
siderably more rare than the squawfish and may be near extirpation in
nature (Tyus 1987). The razorback sucker is protected by the states of
Utah, Colorado, Arizona, Nevada and California.
Colorado squawfish are restricted to the upper basin of the Colorado River
system above Glen Canyon Dam, inhabiting the Colorado and Green rivers and
various large tributaries. The razorback sucker is also largely restrict-
ed to the upper basin, though a remnant population of old adults persists
in Lake Mohave, a lower basin reservoir.
Loss of habitat for these rare fishes has occurred over many years.
Construction of dams and diversions has had a major impact by altering
natural flow and temperature regimes. Habitat in the lower basin has been
altered to such an extent that it no longer supports self-sustaining
populations of Colorado squawfish or razorback sucker (Minckley 1973,
1983). Although the upper basin supports populations of the endangered
fishes, their continued existence there is far from assured. Because
demands for municipal and agricultural water continue to increase, the
accompanying loss of suitable habitat for these fishes in the upper basin
may be paralleling that which occurred in the lower basin. In the upper