8231

• UCREFRP Catalog Number: 8231
• Author: Maddux, H. R.
• Title: Draft Environmental Assessment For Procedures For Stocking Of Nonnative Fish Species In The Upper Colorado River Basin.
• USFW Year: 1996.
• USFW - Doc Type: Grand Junction, CO.
• Copyright Material: NO

(Recovery Program 1996). Stocking of endangered fishes has begun in
areas of low numbers (Recovery Program 1996). However. until problems
associated with nonnative fishes are addressed. it is unlikely tnat the
endangered fishes will be recovered (establishment and protection of
viable. self-reproducing populations).
The fish fauna in most areas of the Colorado River Basin bears little
resemblance to what occurred historically. The geologic isolation of
Basin rivers from other watersheds gave rise to a fish fauna in whicn 64
percent of the native species are found nowhere but in the Basin (Miller
1959). In addition to being unique, with only 36 species of native fish
found in the Basin, the fish fauna is depauperate compared with other
North American river basins. The native fish were adapted to the
pre-development aquatic conditions (e.g. variable flows, high sediment
levels, fluctuating temperatures) found in the Basin. Because there
were only a few different native fish species within a specific habitat.
inter-specific competition for the available resources was likely less
intense.
The changes to Basin rivers resulting from human development activities
have had a major impact on the native fish species. Some native fish
species, adapted to the highly variable aquatic environment of the
pre-development Basin, remained successful in the altered habitats.
However, the creation of these altered habitats has contributed to the
establishment of many nonnative fish species into the Basin. Aggressive
competitors, the nonnative fish species soon dominated most of the
altered Basin habitats. The role of habitat alteration versus nonnative
fish establishment in the decline of native fish populations is unclear.
In less altered river reaches, native fish appear to be able to compete
more effectively with the nonnatives.
The introduction of fish species not native to the Basin began in the
late 1800's. These fishes were introduced for a variety of reasons,
including establishment of sport fish populations, as forage for the
sport fish species, biological control of unwanted pests, aesthetic or
ornamental purposes, release of unwanted pets or bait fish, and
accidental releases (Taylor et al. 1984). Some of these introductions
did not result in the species becoming established. Other introductions
resulted in establishing a species throughout large areas of the Basin.
Some species have been repeatedly stocked as part of recreational
fisheries programs. Introductions have been made by Federal and State
agencies, commercial enterprises, and private citizens.
Nonnative fish species have been clearly implicated in the population
reductions or elimination of native fish species from the Basin's
aquatic habitats (Dill 1944, Osmundson and Kaeding 1989, Behnke 1980,
Joseph et al. 1977, Lanigan and Berry 1979, Minckley and Deacon 1968,
Meffe 1985, Propst and Bestgen 1991. Rinne 1991 and others). Nonnative
fishes have had an adverse impact on endangered fishes throughout the
Basin and in many areas within the Basin it is a primary factor
contributing to poor recruitment and low abundance of native species.
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