9417

• UCREFRP Catalog Number: 9417
• Author: U.S. Department of the Interior.
• Title: Final Environmental Assessment
• USFW Year: 1998.
• USFW - Doc Type: Acquisition and Enhancement of Floodplain Habitats along the Upper Colorado, Green, and Gunnison Rivers as part of the Recovery Program for Endangered Colorado River Fishes.
• Copyright Material: NO

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reducing spring flooding and increasing base flows.
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Changes to the natural nydrograph have altered
aquatic habitats, partichlarly backwaters and
floodplains, considered imPortant to the survival of
native and endangered fishes. In addition, levees
have been built in soine areas, reducing or
eliminating the possibility bf flooding. These levees
do not allow the current Ihydrograph to inundate
floodplain habitats and provide resources for the
survival of larvae.

F. Endangered Fish

F our native fish species lndemic to the Colorado
River system - razorback sucker, Colorado
squawfish, bonytail, and humpback chub - have
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been listed as endangered under the Endangered
Species Act of 1973 as akended. In addition to
altered hydrographs and levee construction, the
endangered fishes in the Upper Basin have been
and continue to be impacted by other factors,
including:

.Iwater depletions resulting
. f I
consumptIve use 0 water,

.Ihabitat degradalion due to
development,

from the

floodplain

.I diversion dams and structures that create
barriers to fish migration I,

.I predation from and competItIon with
introduced nonnative fishes, and
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.Iwater quality and contaminants problems.
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(Maddux et al. 1993; Miller et al. 1982; Wydoski
1980; U.S. Fish and Wildlife Service 1990a & b;
1991).

Various recovery actions are being taken to deal
with water depletions, flow patterns, migration
barriers, nonnative fish sp~cies, and contaminants.
Endangered fish are also b~ing produced and raised
in hatcheries to be stocketl into the wild.

This Environmental Assessment will describe
efforts to acquire and, where warranted, restore
floodplains that will enhance the chances for
survival of endangered and native fishes that remain
or are stocked into the wild, and to maintain and
protect habitat that can sustain recovery of these
fishes over the long tenn. Increased survival of the
larval stages, in particular, is expected to result in
a better chance that many more of these fish will
survive into adulthood. Acquisition of habitat is
considered essential to support endangered fish
recovery. Recovery is defined as achieving and
maintaining natural self-sustaining populations of
specIes.

G. Importance of Floodplain Habitat to the
Recovery of Endangered Fishes

The importance of land-water interface to a river
system's productivity has been recognized for over
twenty-five years (Allan 1995; Hynes 1970; Hynes
1983). The warmth of inundated floodplains,
adjacent to rivers, results in an increased
production of phytoplankton and development of a
food web which supports the river ecosystem
(Welcomme 1979). Warmer water temperatures
combined with greater food production also results
in faster growth rates for young fishes, thereby
increasing the chances of survival because larger
fish are less vulnerable to predation (Bestgen et al.
1997).

Inundated floodplains also provide a quiet-water
shelter from main channel river currents. This
reduction in energy expenditures of young fishes
could be reserved for growth. Inundated floodplain
vegetation also offers hiding places from predators
(Modde 1997). Floods and floodplains are now
understood to be essential components of river
ecosystems (Sparks 1995).

The decline of the four native fish species in
Colorado River has been attributed to a lack of
recruitment. High mortality during early life stages
is believed to contribute to limited recruitment.
Few larval razorback suckers are believed to

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