PERMFILE50679

• Permit No: C1980004A
• IBM Index Class Name: Permit File
• Doc Date: 5/13/2002
• Section_Exhibit Name: APPENDICES K - P
• Media Type: D
• Archive: Yes

• FWSJGJ-6-CO-92-F-007 Page 3
River system. Behnke and Benson (1983) summarized the decline of the natural
ecosystem. They pointed out that dams, impoundments, and water use practices
are probably the major reasons for drastically modified natural river flows
and channel characteristics in the Colorado River Basin. Dams on the mainstem
have essentially segmented the river system, blocking Colorado squawfish
spawning migrations and drastically changing river characteristics, especially
flows and temperatures. In addition, major changes in species composition
have occurred due to the introduction of nonnative fishes, many of which have
thrived as a result of changes in the natural riverine system (i.e., flow and
temperature regimes). The decline of endemic Colorado River fishes seems to
be at least partially related to competition or other behavioral interactions
with nonnative species, which have perhaps been exacerbated by alterations in
the natural fluvial environment.
The Colorado squawfish currently occupies about 1,030 river miles in the
Colorado River system (25 percent of its original range) and is presently
found only in the upper Colorado River Basin above Glen Canyon Dam. It
inhabits about 350 miles of the mainstem Green River from its mouth to the
mouth of the Yampa River. Its range also extends 140 miles up the Yampa River
and 104 miles up the White River, the two major tributaries of the Green
River. In the mainstem Colorado River, it is currently found from Lake Powell
extending about 201 miles upstream to Palisade, Colorado, and in the lower 33
• miles of the Gunnison River, a tributary to the mainstem Colorado River (Tyus
et al. 1982). Recent investigation found adult Colorado squawfish inhabit the
San Juan River as far upstream as 163.3 miles above Lake Powell.
The life stages that appear to be most critical are from egg fertilization
through its first year of life. It has been demonstrated that these phases of
Colorado squawfish development are also closely tied to some specific habitat
requirements. It is imperative that proper flows and temperatures are
provided during these essential life stages. The Conservation Measures
outlined below will help further investigate and meet the habitat requirements
of the Colorado squawfish, thus offsetting project-related impacts and the
likelihood of jeopardy for the species.
Humoback chub
Humpback chub generally do not make migrational movements in the upper
Colorado River and tend to reside throughout the year within a limited reach
of river. Humpback chub are found inhabiting narrow, deep canyon areas, and
are relatively restricted in distribution. They seldom leave their canyon
habitat (Service 1982). While humpback chub are regularly found dispersed in
the Green and Yampa Rivers, the only major populations of humpback chub known
to exist in the upper Colorado River basin are located in Black Rocks and
Westwater Canyons on the Colorado River. Conservation Measures outlined below
will contribute to providing proper habitat conditions for humpback chub, thus
offsetting the likelihood of jeopardy for the species.
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