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

35

restore historic native waters". Some respondents recommended chemical eradication be
used selectively, though several made this recommendation in the context of eradication in
headwater salmonid systems. Chemical eradication was not considered generally applicable
to the large riverine systems occupied by native warmwater fish species including the
endangered species. Two respondents did suggest the use of selective poisoning, and one
further suggested providing nursery habitat by reducing nonnatives with timely poisoning of
key backwaters areas.

Three respondents suggested specialized removal techniques be developed and two
of these persons recommended applying removal to northern pike. Both biologists suggested
a specific effort to remove pike from their spawning habitat or from spring habitat used by
Colorado squawfish in spring prior to their spawning migration. They suggested this removal
might have some limiting effect on the pike. population. Removal of pike was not
considered a means of eliminating the species.

Habitat management

Habitat management relating to flow manipulation was the second most often cited
approach. Nine respondents singularly or in combination with other techniques suggested
manipulation of a regulated flow regime or maintenance of an unregulated flow regime as
a primary element of any strategy to enhance habitat conditions for native fishes over
nonnative fishes. Since most of the introduced species are not true riverine species, the
o,bjective should be to manage for optimal riverine habitat and maintain as much habitat in
pristine condition as possible. These conditions included considerations of native fish
spawning habitat and summer rearing habitat Specifically, the apparent association of
relative spawning success between native and nonnative fishes related to high spring runoff
flows was listed as a potential option. The inhIbiting effect of high spring flows on the
reproductive success of certain prolific nonnative species like red shiner, fathead minnow and
channel catfish was considered: to have value as a population control measure. The effect
of water fluctuation in the river system and its relative effect on native and nonnative fishes
was also mentioned. A recommendation was made that, since certain water conditions may
be more conducive to survival of introduced species than others, we need to accumulate
information on requirements of introduced species as well as natives species. Perhaps water
management strategies can be developed that enhance reproductive success of Colorado
squawfish, for example, but provide less than optimal conditions for one or more of the
introduced species. A caveat to this recommendation indicated the development of water
management strategies along these lines would be very difficult.

Another recommendation concerned isolation of off-channelspawning habitat or
refugia for nonnative species like northern pike, black bullhead, and centrarchid species to
prevent annual escapement into the river during high spring flows.

;
;1

:J