9490

• UCREFRP Catalog Number: 9490
• Author: U.S. Fish and Wildlife Service.
• Title: Final Environmental Assessment for Procedures for Stocking of Nonnative Fish Species in the Upper Colorado River Basin.
• USFW Year: 1996.
• USFW - Doc Type: Grand Junction.
• Copyright Material: NO

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1981), Osmundson (Colorado squawfish eaten by largemouth bass, green
sunfish, black crappie, and black bullhead; 1987), Marsh and Brooks
(razorback sucker eaten by channel and flathead catfishes; 1993);
~, Ruppert et al. bluehead sucker eaten by red shiner; 1993); Crowl and
Lentsch (Colorado squawfish eaten by northern pike; 1995), Mueller
(razorback sucker eaten by sunfishes and largemouth bass; 1995), Muth
and 8eyers (Colorado squawfish and razorback sucker larvae eaten by
channel catfish and green sunfish; in press), Nesler (roundtail chub,
speckled dace, bluehead and flannelmouth suckers eaten by northern
pike; 1995), and Valdez and Ryel (humpback chub eaten by brown and
rainbow trouts and channel catfish; 1995). Razorback sucker eggs and
larvae are eaten b~ channel catfish, green sunfish and carp (Medel-
Ulmer 1983, Hinckley 1983, Langhorst 1981, Marsh and Langhorst 1988)."
~; The other potential effects to native fish from nonnative species are
more difficult to quantify. Harassment of native species by nonnative
fish can include nonpredatory attacks that disrupt sheltering, breeding
or feeding behavior or the elimination of habitat features (e.g.
aquatic vegetation) utilized by the native species. These types of
actions make it more difficult for the native fish to successfully
utilize a specific habitat, thus contributing to declines in or the
local extinction of the population. The role of nonnative fish
introductions in the spread of new diseases and parasites in the Basin
has not been fully evaluated. The spread of the parasite ernes sp. in
the Basin is very likely the result of nonnative introductions.
The continued stocking of nonnative fish, even those already
established in the Basin, adversely affects the native fish species.
The stocking may enable a species to maintain a higher population level
than the habitat could support, increasing the effectiveness of
competition against the native species. In cases where natural events
such as drought or floods have reduced nonnative fish populations,
stocking allows them to regain pre-event population levels faster than
would occur naturally. This may suppress native fish recovery in the
area. However, it should be noted that at present, very little
warmwater stocking occurs in Utah and Wyoming.
A. No Action Alternative
1. Aquatic Biological Resources: Although Utah and Wyoming have no
current plans for stocking warmwater fishes in the Upper Basin, with no
stocking procedures in place future stockings could occur. As such
stockings occur, nonnative fish occurrence in the river would increase.
Additionally, determinations could be made to introduce new species
into the basin. In the recent past, Utah has considered impacts to the
endangered fishes even though no stocking procedures have been in
place. Utah considered stocking rainbow smelt into Lake Powell to
improve recreational fishing, but through a review process, tabled
their proposal because of concerns on the downstream humpback chub
population. In the past, Wyoming has stocked channel catfish into the
Little Snake River. They stopped stocking in 1990, when a Colorado
squawfish was captured in the Wyoming portion of the Little Snake

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