7849

• UCREFRP Catalog Number: 7849
• Author: Nesler, T. P.
• Title: Interactions Between Endangered Fishes And Introduced Gamefishes In The Yampa River, Colorado, 1987-1991.
• USFW Year: 1995.
• USFW - Doc Type: Final Report, Colorado River Recovery Implementation Program Project No. 91-29 and Federal Aid Project SE-3,
• Copyright Material: NO

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 squawfish Ptychocheilus lucius, humpback chub Gila cypha,
bonytail Gila elegans, and razorback sucker Xyrauchen texanus (see Hawkins and Nesler 1991).
Gamefish species such as northern pike Esox lucius, channel catfish Ictalurus punctatus,
largemouth bass Micropterus salmoides, and others are implicated as part of the problem for
native fishes due to their predatory nature. As indicated in Hawkins and Nesler (1991), evidence
of documented predation or competitive advantage of non-native fishes over the endangered
fishes was limited prior to 1990 to situational occurrences in artificial settings where native
fishes were reared in large numbers or in confmed areas, or after stocking of hatchery-reared
native fishes (Osmundson 1987, Hendrickson and Brooks 1987, Marsh and Langhorst 1988,
Marsh and Brooks 1989). Investigations of negative interactions between non-native fishes and
the endangered fishes, including this study, have received greater emphasis by the Upper
Colorado River Recovery Program since Hawkins and Nesler (1991) provided recommendations
for studying specific interactions with select non-native species in laboratory or controlled field
experiments and followed by investigations to confrrm these results in the wild.

Management plans targeting reduction of gamefish species as a control measure will pose
added difficulties due to the value and public popularity of associated sportfisheries. The
primary focus of this study was to determine life history patterns and requirements of warmwater
gamefish species in the Yampa and Colorado rivers in Colorado to establish how well
populations of these non-native fishes are adapting to the riverine environment, and to evaluate
seasonal habitat use and prey selection of the non-native gamefishes for evidence of potential
impacts from predation and competition upon the endangered fishes. Knowledge of limitations
imposed on thesegameflSh species by environmental conditions in these two rivers will help
defme the problems posed by these species on the native fishes. This knowledge may also
indicate recovery measures necessary to minimize negative interactions with the endangered
fishes.

The scope of this study included northern pike, channel catfish, and smallmouth bass
Micropterus dolomeiu in the Yampa River and channel catfish, largemouth bass, green sunfish
Lepomis cyanellus, and black bullhead Ameiurus melas in the Colorado River. This report is
confmed to the results obtained in the Yampa River. Results of the Colorado River portion of
the study will be provided in a separate report.

STUDY GOAL AND OBJECTIVES

Goal: to determine the impact of non-native, warmwater gamefish species via predation
and competition upon Upper Colorado River Basin endangered fish species.

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