9547

• UCREFRP Catalog Number: 9547
• Author: Tyus, H. M. and J. F. S. III.
• Title: An Evaluation of Recovery Needs for Endangered Fishes in the Upper Colorado River, with Recommendations for Future Recovery Actions - Final Report.
• USFW Year: 1999.
• USFW - Doc Type: Glenwood Springs, CO.
• Copyright Material: NO

EXECUTIVE SUMMARY
~ Native fishes of the upper Colorado River (UCR) basin are declining in abundance due
to anthropogenic alterations to physical and biological components of the natural
riverine environment. Two primary agents of environmental change have been water
resource development and the introduction of nonnative fishes. Construction and
operation of many dams, reservoirs, and diversions throughout the UCR basin have
altered the historic hydrograph, fragmented habitat by blockage, converted riverine to
lacustrine habitat, and changed water quality characteristics (especially temperature
and sediment transport). Concurrent with water resource development, many
nonnative fish species have been introduced in the Colorado River system. Some of
the introduced species are aggressive competitors and predators that occupy habitats
essential for native riverine fishes. Although water resource development undoubtedly
~ has taken a toll on the physical habitat of the native fishes, the presence, proliferation,
and continued addition of nonnative fishes to the river system is arguably the greatest
threat to native fish populations.
The big river fish community has been greatly affected by recent habitat change. As a
~ result, four species of have declined so greatly in abundance and geographical
distribution that they are now listed as endangered under provisions of the Endangered
Species Act. Efforts to recover these four fishes are led by the U.S. Fish and Wildlife
Service, which established recovery teams, completed recovery plans, and determined
critical habitat pursuant to provisions of the Act. However, recovery issues related to
~ physical habitat have been contentious. Perceived recovery needs have constrained
future water development in an area where seven state governments participate in
water allocation through interstate compacts and other legal agreements. Issues
related to control of nonnative fishes also have been nettlesome, in part due to
jurisdictional concerns of state agencies. Resolution of these issues, in part, will require
clarifying the scientific rationale for recovery and by establishing priorities for future
~ actions.
Much has been learned about the life history requirements of endangered big river
fishes during the past twenty years. However, despite large investment in research and
numerous management actions, there has been no apparent success toward recovery,
if judged on the basis of increasing the abundance and distribution of endangered
fishes. Instead, another fish (razorback sucker) has been listed during this period and
natural bonytail populations have virtually disappeared. The razorback sucker has
suffered from poor or no recruitment for many years, and the number of fish in the wild
has declined sharply, especially in the UCR where. very few individuals remain. There
are so few bonytail remaining in nature that for all practical purposes the species is
functionally extinct, i.e., it is essentially extirpated from the upper Colorado River basin.
The remaining two species have fared better. Extant populations of humpback chub
appear to be relatively stable in size, but the species now has a very restricted
geographical distribution. The number of Colorado pikeminnow (formerly Colorado
v