9391

• UCREFRP Catalog Number: 9391
• Author: Watts, G., W. R. Noonan, H. R. Maddux and D. S. Brookshire.
• Title: The Endangered Species Act and Critical Habitat Designation
• USFW Year: 1997.
• USFW - Doc Type: An Integrated Biological and Economic Approach.
• Copyright Material: NO

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endangered fishes in each river system and their habitat needs are similar both studies cover
multiple species. The four listed fish species in the Colorado River basin are the Colorado
squawfish (Ptychocheilus Lucius), the razorback sucker (Xyrauchen texanus), the humpback
chub (Gila sypha), and the bony tail (Gila elegans). The Virgin River listed species are the
woundfm (Plagopterus argentissimus) and the Virgin River chub (Gila seminuda). 3

Endemic fish populations in both study regions have been declining since the turn of the
century. The declines are a result of physical and biological changes in the river systems:
stream flow alterations, habitat fragmentation and modification, contaminants, and competition
with and predation by introduced non-native fish. The natural hydrography of the systems
have been significantly altered by the construction of dams and increasing consumptive water
uses. Current consumptive water uses include agricultural, municipal and industrial, and
reservoir evaporation (Maddux et al. 1993, 1995). In order to enhance consumption over
time, a series of dams have been constructed throughout the Colorado River system. A total
of 43 major dams and diversions that have been constructed.

Determination of critical habitat requires consideration of physical and biological features that
are essential to species conservation. The critical habitat designated in both river basins was
aimed at creating biological conditions that enhance the constituent elements for the target
species. These features, referred to as constituent elements, include: (1) space for populations;
(2) food, water, or other nutritional or physiological requirements; (3) cover or shelter; (4)
sites for breeding, reproduction, and rearing of offspring; and (5) habitats that are protected
from disturbance or are representative of the historical and ecological distribution of species.

J The Colorado squawfIsh and the humpback chub were listed as endangered species on March 11, 1967
(32 Federal Register 4(01), and thus were originally listed under the auspices of the Endangered Species
Preservation Act of 1966. The razorback sucker was listed as endangered on October 23, 1991 (56 Federal
Register 54957), the bonytail on April 23, 1980 (45 Federal Register 27713). The listing of the woundfm
occurred on October 13, 1970 (35 Federal Register 16047), and the listing of the Virgin River chub on August 24,
1989 (54 Federal Register 35305).

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