7981

• UCREFRP Catalog Number: 7981
• Author: Tyus, H. M.
• Title: Management of Native Warmwater Fishes of the Upper Colorado River. pages 175-182, in Warmwater Fishes Symposium I. Technical Report RM-207.
• USFW Year: 1991.
• USFW - Doc Type: \
• Copyright Material: YES

f,

J~ ~S
I tqC{ /

Management of Colorado River Fishes1

Harold M. Tyus2

. Abstract.--Native warmwater fishes of the upper Colorado
Rlver basin have declined, and four big-river fishes are in
danger of extinction. Of these, Colorado squawfish Ptvchocheilus
lucius, humpback chub Gila ~, and bony tail g... eleoans
are listed as federally-endangered, and razorback sucker
Xvrauchen texanus, is proposed for listing. Rare status,
continuing habitat change, and lack of-knowledge about their
habitat needs have made management programs difficult to
develop and implement. Recent efforts to recover the listed
fishes have provided some information about all of the native
fishes and prompted some management activities. The future of
native Colorado River fishes is uncertain, but efforts of an
interagency recovery implementation program offers some hope
for them.

INTRODUCTION

have been severly altered by man. Construction
of large mainstream projects began in the early
1900s (Fradkin 1981; Carlson and Muth 1989),
and by the 1960s, much of the mainstream
Colorado River had been converted into a system
of dams and diversions. As a result, the timing,
duration, and magnitude of flows of most r'vers
of the Colorado River basin have been
substantially altered. Today, most mainstream
areas little resemble their natural condition
with respect to native fish habitats.

Native North American fishes are
declining in species and population abundance.
During the past 100 years, 3 genera, 27 species
and 13 subspecies of fishes have become extinct,
and an additional 364 rare fishes are threatened
(Williams et ale 1989). Stream fishes have been
especially impacted, because there are few
rivers remaining in North America whose annual
flow patterns have not been severely altered. It
is unknown whether the rate of loss of stream
faunas can be reduced. The fate of native
Colorado River fishes in the Southwestern United
States is of particular concern, due to a
Widespread and drastic habitat loss which has
severely impacted this unique fauna.

The Colorado River basin comprises about
12% of the land mass of the continental United
States. Located in extremely arid country, its
waters are considered a precious commodity
(Fradkin 1981; Carlson and Muth 1989) and they

These habitat changes were associated with
the decline of native species and proliferation
of non-native forms introduced by man (Minckley
1982; Tyus et ale 1982; Carlson and Muth 1989).
The disappearance of native fishes from greatly
altered habitats were associated with an
invasion by other species, and these changes
have ostensibly occurred too quickly for native
forms to adapt and recover (Minckley and Deacon
1968; Molles 1980). The causes for declines of
endangered fish stocks in less-altered habitats
are not as obvious and they are even more
difficult to determine.

'Paper presented at the first Warmwater
Fishes Symposium, Scottsdale, Arizona, June 6
1991. '

2Harold M. Tyus is Project Leader of the
Colorado River Fishes Project, U. S. Fish and
Wildlife Service, Vernal, Utah.

The U.S. Fish and Wildlife Service (USFWS)
has been in consultation with other federal
agencies in the upper Colorado River basin under
provisions of the Endangered Species Act of 1973
as amended, and has issued over 100 Biological
Opinions pursuant to Section 7 of that Act (Rose
and Hamill 1988). In general, USFWS has
determined that water depletions and dam

t15

07 qg J

~