Economic Analysis of Critical Habitat Designation in the Colorado River Basin for the Razorback Sucker, Humpback Chub, Colorado Squawfish, and Bonytail April 1994

• Description: Economic Analysis of Critical Habitat Designation in the Colorado River Basin for the Razorback Sucker, Humpback Chub, Colorado Squawfish, and Bonytail April 1994
• State: CO
• Basin: Colorado Mainstem
• Date: 4/1/1994
• Title: Economic Analysis of Critical Habitat Designation in the Colorado River Basin for the Razorback Sucker, Humpback Chub, Colorado Squafish, and Bonytail April 1994
• Water Supply Pro - Doc Type: Report/Study

include, but are not limited to, alterations adversely modifying any of those physical or
biological features that were the basis for determining the habitat to be critical.
B. Listing History and Habitat Designations
1. Listing History
The Colorado squawfish and humpback chub were listed as endangered species on March 11,
1967 (32 FR 4001). The bonytail was listed as endangered on April 23, 1980 (45 FR
27713). On May 16, 1975, USFWS published a notice of its intent to determine critical
habitat for the Colorado squawfish, humpback chub, and numerous other species (40 FR
21499). On September 14, 1978, USFWS proposed critical habitat for the Colorado
squawfish (43 FR 41060). The proposed area included 623 miles of the Colorado, Green,
Gunnison, and Yampa rivers. This proposal was later withdrawn (44 FR 12382; March 6,
1979) to comply with 1978 amendments to the Act (16 U.S.C. 1531 et seq.), that required
USFWS to include critical habitat in the listing of most species and to complete the listing
process within 2 years from the date of the proposed rule or to withdraw the proposal from
further consideration. USFWS did not complete the listing process within the 2 -year
deadline. The razorback sucker was proposed for listing as a threatened species on April 24,
1978 (43 FR 17375). The proposal was withdrawn on May 27, 1980 (45 FR 35410) in
accordance with 1978 amendments to the Act that require a determination of critical habitat
in the listing of most species. The razorback sucker was listed as endangered in 1991 (56
FR 54957). Critical habitat for all four endangered species was proposed on January 29,
1993 (58 FR 6578).
2. Historical and Current Habitat
a. Razorback Sucker
The razorback sucker is part of a unique fish fauna endemic to the Colorado River Basin.
Historical riverine systems provided a wide variety of habitats that razorback suckers
occupied, including backwaters, sloughs, and oxbow lakes. The razorback sucker was once
abundant throughout the 3,500 miles of the Colorado River Basin, primarily in the mainstem
of the Colorado River and its major tributaries in Arizona, California, Colorado, Nevada,
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