8031

• UCREFRP Catalog Number: 8031
• Author: U.S. Department of the Interior.
• Title: Fish and Wildlife Service Final Biological and Conference Opinion on Lower Colorado River Operations and Maintenance - Lake Mead to Southerly International Boundary.
• USFW Year: 1997.
• USFW - Doc Type: \
• Copyright Material: NO

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BIOLOGICAL OPINION

Status of the Species

was tied closely to the hydrologic cycle of the river. As flows rose and began to create nursery
habitat, spawning occurred, Ample space and food was provided for the young fish.

Conversely, clear water impoundments provided ideal habitat for a variety of non-native fish.
Impoundments and severely modified flows interrupted this creation of habitat critical for survival.
Non-native fish were introduced and rapidly became established throughout most of the Lower
Basin. Non-natives were effective competitors and predators on native fish. As a result,
essentially all the native fish species are either listed as threatened or endangere d or their numbers
have decreased significantly.

A summary discussion on the species' response to the proposed action is provided for the two
endangered fish species following the fish critical habitat section.

Critical Habitat - Bonytail Chub and Razorback Sucker

Critical habitat is defmed in the ESA to include areas whether occupied or not that are essential
to the conservation of the species. Conservation is defined in the ESA as that needed to bring
about the complete recovery of the species. Efforts to designate critical habitat began with the
proposed rule to list the razorback sucker in 1990.

The May 22, 1990, proposed rule to list the razorback sucker did not contain a proposal to
designate critical habitat. The fmal rule listing the razorback sucker as an endangered species
stated that critical habitat was not determinable at the time of listing. This gave the Service an
additional year to obtain further habitat information. On October 30, 1991, the Service received
a notice of intent to sue from the Sierra Club Legal Defense Fund over failure to desig nate critical
habitat at the time of listing, After review of additional information available, the Service
concluded on December 6, 1991, that designation of critical habitat was both determinable and
prudent. After a ruling that the Service had violated the ESA by not designating critical habitat
with the listing of the species, the U. S. District Court in Denver, Colorado, ordered the Service
to publish a proposed rule to designate critical habitat within 90 days of the Court I s order.

The Service determined that since the habitats of the razorback sucker overlapped with those of the
bonytail chub, Colorado squawfish (Ptychocheilus lucius) and humpback chub (Gila cypha), and
the issues facing these species were very similar, that designating critical habitat for all four specie s
at the same time would be appropriate. The proposed rule was published on January 29, 1993, and
contained proposed critical habitat for the four listed native Colorado River fish. The final rule
to designate critical habitat was published on March 21, 1994, with an effective date of April 20,
1994.

Critical habitat for the bony tail chub includes portions of the Colorado, Green, and Yampa Rivers
in be occupied at the time of designation. Within the project area, critical habitat includes the

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