9554

• UCREFRP Catalog Number: 9554
• Author: Monroe, L. and T. Hedrick.
• Title: Northern Pike ‎(Esox lucius)‎ Control in the Middle Green River, Utah 2001-2006.
• USFW Year: 2008.
• USFW - Doc Type: 109,
• Copyright Material: NO

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INTRODUCTION

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Nonnative fishes have become established in rivers of the upper Colorado River basin,

with certain species implicated in the reduction in distribution and abundance of native fishes,

primarily through predation and competition (Hawkins and Nesler 1991; Lentsch et al. 1996;

Tyus and Saunders 1996). The Upper Colorado River Endangered Fish Recovery Program

(Program) has determined that control of nonnative fish in the upper Colorado River basin is

essential to the recovery ofthe four endangered fish species: Colorado pikeminnow

(Ptychocheilus lucius), razorback sucker (Xyrauchen texanus), humpback chub (Gila cypha), and

bony tail (Gila elegans). Experts in the Upper Colorado River Basin have rated northern pike

(Esox lucius) as one of the six nonnative species of greatest concern (Hawkins and Nesler 1991).

It is thought that northern pike were originally introduced as a game fish in Elkhead

Reservoir, a small reservoir on Elkhead Creek (a tributary to the Yampa River in northern

Colorado), in 1977 (Figure 1). The subsequent invasion of the Yampa River was likely due to

this original introduction into Elkhead Reservoir (Tyus and Beard 1990). However, Hawkins et

al. (2005) hypothesize that Elkhead Reservoir was not the original source of northern pike in the

Yampa River due to discrepancies in stocking records from this period. Regardless, since the

original invasion, northern pike have established a reproducing population in the upper Yampa

River and have expanded their numbers and range throughout this river (Tyus and Beard 1990).

Pike were not found in the Green River until after this initial invasion suggesting that the species

moved downstream from the Yampa River into critical habitat of the Green River (Tyus and

Beard 1990; Hawkins et al. 2005). Here, as in the Yampa River, they pose a competitive and

predatory threat to the endangered fishes. Since 2001, Division of Wildlife Resources (Division)

data show that four tagged northern pike ranging from 720 mm to 826 mm have moved from the

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