7025

• UCREFRP Catalog Number: 7025
• Author: Hawkins, J. A. and T. P. Nesler.
• Title: Nonnative Fishes in the Upper Colorado River Basin
• USFW Year: 1991.
• USFW - Doc Type: An Issue Paper.
• Copyright Material: YES

7
LITERATURE REV1EW

General trends in abundance of nonnative fishes

Distributions of fishes introduced into the upper basin were shown on maps provided
by Tyus et al. (1982) and further discussed by Carlson and Muth (1989). Documented
reports of decreasing numbers of native and increasing numbers of nonnative fish are
numerous; however, it is unclear whether direct cause and effect relationships exist. Several
examples follow that identify an increase of nonnative fishes concurrently with a decrease
of native fishes

In three study areas on the upper Colorado and lower Gunnison rivers, Colorado,
Osmundson and Kaeding (1989a) noted that young native fishes progressively decreased in
abundance from 1986 through 1988, while introduced fishes, especially red shiner, fathead
minnow, and larval sand shiner, progressively increased in abundance. These trends in
abundance may have been related to annual differences in flow, i.e., 1986 was identified as
a high flow year, 1987 an average flow year, and 1988 a low flow year.

Behnke (1980) noted that an increase in redside shiner abundance occurred
concurrently with the decline of Colorado squawfish in the Green and Yampa rivers, Utah
and Colorado, and suggested that redside shiner had caused the decline. Holden (1977)
disagreed with this conclusion by noting that redside shiner were abundant in the 1960s when
Colorado squawfish reproduction was apparently successful.

The introduction and increase of northern pike and walleye in the Green River, Utah
was documented by Tyus and Beard (1990). Originally introduced into a Yampa River
tributary reservoir in 1977, northern pike invaded the Green River by 1981. Since that time,
they have increased in both range and abundance. Walleye were presumably established in
the Green River drainage in the 19605 by fish stockings in Duchesne River, Utah reservoirs.
Although widely distributed in the Green River, their numbers remain low but stable (Tyus
and Beard 1990).

The Yampa River provides another example of the abundance and distribution of
nonnative fish species. Miller et al. (1982b) studied the lower 206 kilometers (km) of the
Yampa River to its confluence with the Green River. Of 24 fishes collected, 15 were
introduced. Native fishes were more common within Yampa Canyon in Dinosaur National
Monument than other areas. Species diversity increased upstream as more nonnative fishes
were collected. They disagreed with Joseph et al. (1977) who implied that lack of
documented Colorado squawfish reproduction since 1969 was correlated with increasing
numbers of redside shiner, the dominant species in 1975-1976. Implications made by Joseph
et a!. (1977) were questioned because all collections were made in upper reaches, upstream
of documented Colorado squawfish reproduction (Miller et al. 1982b). The most abundant
species collected in Dinosaur National Monument by electrofishing and angling between
1987-1989, were common carp and channel catfish (Karp and Tyus 1mb).

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