8056

• UCREFRP Catalog Number: 8056
• Author: Hamill, J.
• Title: Restoring and Protecting Instream Flows for Endangered Fish in the Upper Colorado River Basin.
• USFW Year: 1992.
• USFW - Doc Type: Denver, CO.
• Copyright Material: NO

Introduction

An understanding of the strategies and problems associated with
providing instream flows for the endangered Colorado River fish
requires an appreciation of the fish, why they are endangered,
and the importance of the Colorado River as a source of water for
municipal, industrial, and agricultural purposes. The Colorado
River yields less water per square mile than any other major
river in the United states, yet provides 25 million people with
water for municipal, agricultural, industrial, and recreational
purposes. Water in the basin has been completely divided up
between the upper and lower basin states according to Interstate
Compacts made in 1922 and 1948. Dozens of large dams have been
constructed to harness the flows in the basin and make those
flows available for consumptive (beneficial) use. The river has
been altered to control its water to the point that it has been
described as the most heavily used, controlled, and fought over
river in the world.

Several unique large river fish evolved in the turbulent,
sediment laden rivers in the Colorado River Basin. Seventy-four
percent of the native fish fauna is endemic to the Colorado
River. Four of the endemic Colorado River fish--the Colorado
squawfish, the humpback chub, the bony tail chub, and the
razorback sucker--are now threatened with extinction due to low
numbers and inadequate recruitment. All four are listed as
endangered under the Endangered Species Act. Two others, the
flannelmouth sucker and the roundtail chub, are identified as
candidate species for listing under the Endangered Species Act.

These fish are endangered because they have been unable to adjust
to the changes in the environment brought about by the activities
of man. Changes in streamflow and water temperature, direct loss
of habitat due to inundation by reservoirs, blockage of migration
routes, and interaction with introduced, nonnative fish species
(predation and competition) are the primary factors responsible
for the decline of these native fish that once ranged throughout
the Colorado River Basin.

The plight of the native fish in the Colorado River Basin is not
an isolated problem. The extinction of 3 genera, 27 species and
13 subspecies have been documented in North America during the
past century (Miller et ale 1989). According to the American
Fisheries Society, over 364 fish in Canada, the united States,