9591

• UCREFRP Catalog Number: 9591
• Author: Nesler, T. P.
• Title: Interactions Between Endangered Fishes and Introduced Gamefishs in the Colorado River, Colorado, 1986-1991.
• USFW Year: 2002.
• USFW - Doc Type: 91-29,
• Copyright Material: NO

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INTRODUCTION

The introduction and establishment of non-native fish species in rivers of the Upper
Colorado River Basin is considered one of the primary contributing factors in the decline and
endangered status of Colorado pikeminnow Ptychocheilus luaus, humpback chub Gila cypha,
bonytail Gila elegans, and razOIback sucker Xyrauchen texanus (USFWS 2000). Gamefish species
such as channel catfish Ictalurus punctatus, largemouth bass Micropterus salmoides, and other
sunfish (Centrarchidae) species have been implicated as part of the problem in the recovery of the
endangered fIShes due to their predatory nature (Hawkins and Nesler 1991). As such, control of
these and other non-native fish species is a primary emphasis, along with habitat restoration,
propagation and stocking, and instream flow management, within the recovery program for the
four endangered fish species. In the strategic plan for the control of non-native fishes in the
Upper Colorado River Basin (Tyus and Saunders 1996), "control" has been defined as "reducing
the numbers of one or more non-native species to levels below which they are no longer an
impediment to the recovery of endangered fISh species." The objective of control actions targeting
non-native fishes is to increase the distribution and abundance of the endangered fishes and
contribute to their recovery (Tyus and Saunders 1996).

The primary focus of this study was to determine population patterns and characteristics
of wannwater gamefish species in the Colorado River in Colorado to establish how well
populations of these non-native fishes have adapted to the riverine environment. This approach
included evaluation of backwater habitat use and prey selection of the non-native gamefishes for
evidence of direct or potential impacts from predation and competition upon the endangered
fishes. Knowledge of environmental limitations for populations of these non-native gamefish
within the Colorado River, and the problems these species pose for native fishes, is expected to
aid in directing control actions for gamefish populations.

The scope of this study included gamefish species in the Yampa River, and channel
catfish, largemouth bass, green sunfish Lepomis cyanellus, and black bullheadAmeiurus melas in
the Colorado River. The Yampa River study was previously reported in Nesler (1995). This
report focuses on Colorado River results, and concludes the investigations initiated in 1987 under
the Recovery Implementation Program Project No. 91-29 and Federal Aid Project SE-3. Due to
the 100year time lag between the field activities and final report for this investigation, new
information has become available from numerous Recovery Program projects that have relevance
to the objectives, conclusions and recommendations of this project. As such, discussion of the
fmdings . of these later studies and comparison to the results of this study is possible. Some
recommendations made for nonnative fish control based on the results of this study have already
been implemented and final reports evaluating effectiveness are nearing completion. The
opportunity to use subsequent years of new information on nonnative fish control enabled
discussion of results to far exceed that pertaining to these results alone. The author felt the
discussion, conclusions and recommendations of nonnative fish control in the Colorado River
based on this larger body of relevant results provided a useful perspective and hindsight that
should be incorporated here.

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