7984

• UCREFRP Catalog Number: 7984
• Author: Maddux, H. R., L. A. Fitzpatrick and W. R. Noonan.
• Title: Colorado River Endangered Fishes Critical Habitat - Draft, Biological Support Document.
• USFW Year: 1993.
• USFW - Doc Type: Salt Lake City, Utah.
• Copyright Material: NO

floodplain, which when inundated provide spawning, nursery, feeding and rearing habitats,
or access to these habitats.
Biological Environment--Food supply, predation, and competition are important elements of
the biological environment and are considered components of this constituent element. Food
supply is a function of nutrient supply, productivity, and availability to each life stage of the
species. Predation, although considered a normal component of this environment, may be
out of balance due to introduced fish species in some areas. This may also be true of
competition, particularly from nonnative fish species.
These primary constituent elements are interrelated in the life history of the four endangered
fishes. This relationship was a prime consideration in selection of proposed critical habitat
for the fishes.
Critical habitat may only be seasonally occupied by the fish, but such habitat may be
important for their conservation. Life history requirements of the Colorado squawfish and
razorback sucker include inundated backwaters and floodplain areas which provide feeding
and nursery habitat when inundated to include these areas. Proposed critical habitat for these
two species includes the 100-year floodplain. Only those areas in the 100-year floodplain
that contain the constituent elements will be considered part of critical habitat.
ADDITIONAL SELECTION CRITERIA FOR THE RAZORBACK SUCKER
Because a recovery plan for the razorback sucker has not yet been prepared, additional
selection criteria were developed to assist the Service in making a determination of which
areas to propose as critical habitat. Previous Service findings, other published and
unpublished literature sources, and discussions with individual members of the Colorado
River Fishes Recovery Team were utilized to develop the constituent elements and additional
selection criteria.
The razorback sucker has displayed a degree of versatility in its ability to survive and spawn
in different habitats. However, razorback sucker populations continue to decline and are
considered below the survival level (moving in direction of extinction). Thus, as versatile as
the razorback sucker appears to be in selecting spawning habitat, there has been little
recruitment of young to the adult population. Therefore, special consideration was given to
habitats required for its reproduction and recruitment.
The following selection criteria were used by the Service to help determine areas necessary
for survival and recovery of the razorback sucker.
1. Known or suspected wild spawning populations, although recruitment may be
limited or nonexistent.
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