7282

• UCREFRP Catalog Number: 7282
• Author: U.S. Fish and Wildlife Service, R. I. P.
• Title: Final Recovery Implementation Program for Endangered Fish Species in the Upper Colorado River Basin.
• USFW Year: 1987.
• USFW - Doc Type: Denver, Colorado.
• Copyright Material: NO

Nonnative fishes directly or indirectly compete with native species for
available resources, such as food and space. The northern pike, for example,
appears to occupy a similar niche as the squawfish in the upper Green River.
Channel catfish, fathead minnow, various shiners, largemouth bass, and the
green sunfish may also compete for habitat. Data indicate direct competition
between young squawfish and the redside shiner in nursery areas, and predation
from largemouth bass and green sunfish upon young Colorado squawfish is also
documented. Predation data is also available on razorback suckers.
Backwaters, the same habitat type important to young-of-the-year and juvenile
squawfish, are often dominated by nonnative species. These nonnative fishes
also thrive in gravel pit ponds, manmade side channels, etc., where water is
warmer and food is more abundant, the same attributes that attract young
squawfish. When these resources are limited, predation and competition
result.
4.4.1 Control of Nonnative Fish
Management of river flows may prove to be the most useful method to provide an
advantage to native species. For example, during the flow years of 1983 and
1984, native fishes reproduced successfully, while nonnative reproduction
appeared to be reduced from previous years.
Stocking of most introduced species has been greatly reduced in recent years.
Further curtailment of stocking and reduction or elimination of some nonnative
species have also been suggested as options to reduce some negative impacts to
rare fish. This will likely have a limited impact, however, because most of
these nonnative species are successfully reproducing in the wild. Control of
stocking or use of live bait of any competing or depredating nonnative species
may be most useful, since it would reduce population augmentation, except from
the wild. Elimination or removal of nonnative species would require a massive
.effort, although the treatment of selected reaches may be feasible, e.g., in
grow-out pond situations (see Section 4.3.4).
Further study on the role of competition and predation between nonnative and
rare species is necessary to further identify nonnative species of concern,
the extent of the problem, and potential solutions.
4.4.2 Saortfishinn
The primary reason for introducing some of these nonnative species is to
create and support sportfishing for both warm and cold water species. Some of
these nonnative sport species may also compete with or prey upon rare species.
The relationships between these species and the rare fish will be studied, as
mentioned in the preceding section.
Though there is minimal overlap between cold water fish species (particularly
salmonids) and rare species habitat, management for sport fish can also
displace native fishes. For example, releases of colder water from
reservoirs, such as Flaming Gorge, have created habitat for cold water sport
fishes rather than for native fishes. This may be a factor below any major
dam or diversion structure, e.g., Flaming Gorge and others. Where feasible,
fish passages and warmer water releases have been recommended to offset some
impacts of sport fish management in areas where rare fish currently occur.
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