8119

• UCREFRP Catalog Number: 8119
• Author: Valdez, R. A. and B. R. Cowdell.
• Title: Effects of Flow Regulation and Ice Formation on Overwinter Nursery Habitat and Survival of Age-0 Colorado Squawfish in the Green River Below Flaming Gorge Dam - Draft.
• USFW Year: 1996.
• USFW - Doc Type: Logan, Utah.
• Copyright Material: NO

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1.0 INTRODUCTION

1.1 Purpose And Objectives

The purpose of this study was to detennine the effect of winter flow regulation and ice formation on
nursery habitat and survival of age-O Colorado squawfish ~tychocheilus lucius) in the Green River
downstream of Flaming Gorge Dam. The principal hypothesis was:

Ice development in backwaters significantly reduces habitat availability and therefore
reduces overwinter survival of age-O Colorado squawfish in one of the primary
nurseries on the Green River downstream of Flaming Gorge Dam.

This investigation was Study #FG-l 0 of the Recovery Implementation Program for Endangered Fish
Species in the Upper Colorado River Basin (Recovery Program). The study was conducted for 3
years under Contract No. 90-2558 with the Utah Division of Wildlife Resources (UDWR), in
cooperation with the Flaming Gorge Work Group.

The objectives of the study were to:

1. Determine overwinter availability of nursery backwater habitat for age-O Colorado
squawfish,

2. Detennine condition and longevity of backwaters exposed to winter flow regulation
and ice formation,

3. Relate flow and ice conditions to overwinter survival of age-O Colorado squawfish,
and

4. Recommend winter flows to protect nursery habitat of age-O Colorado squawfish.

1.2 Background

The Green River and its tributaries in the upper Colorado River basin historically supported 13 native
fish species (Iyus et al. 1982). Eight warmwater species are native to the river below Flaming Gorge
Dam, including Colorado squawfish (Ptychocheilus lucius), humpback chub (Gila ~), bonytail
(Gila elegan&), roundtail chub (Gila robusta), speckled dace ffi.binichthys osculus), razorback sucker
(Xyrauchen texanus), flannelmouth sucker (Catostomus latipinnis), and bluehead sucker (Catostomus
discobolus) (Holden and Stalnaker 1975). Following completion of the dam in 1964, numbers and
distribution of these warmwater species were reduced by altered flow regimes, inundated habitat,
blocked passage, and modified water chemistry and temperature, along with increasing numbers of
non-native fishes (Vanicek 1967, Miller et al. 1982).

Colorado squawfish, humpback chub, bonytail, and razorback sucker are now classified as
endangered, under the Endangered Species Act of 1973, as amended, and roundtail chub and

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