7337

• UCREFRP Catalog Number: 7337
• Author: Valdez, R. A., R. J. Ryel and R. Williams.
• Title: Endangered Fishes of Cataract Canyon
• USFW Year: 1986.
• USFW - Doc Type: The Importance of the Colorado River above Lake Powell to the Colorado Squawfish, Humpback Chub, and Bonytail.
• Copyright Material: NO

ABSTRACT

A fisheries investigation of Cataract Canyon, upper lake Powell, and
the lower Green River in 1985 yielded all three endangered fishes of the
upper Colorado River basin, including Colorado squawfish and humpback chub
of all ages, as well as a possible juvenile and a possible adult bony tail.
Over 671 of the 509 YOY squawfish were captured in the lower 41.8 miles of
the Green River, while 301 were taken with-in Cataract Canyon and only 31
came froll upper Lake Powell. This suggests that reproduction in this region
of the upper basin occurs primarily in the Green River, but the size and
distribution of YOY also indicates spawning in Cataract Canyon and possibly
upper lake Powell. YOY in this region in 1985 hatched primarily the first
of July. These fish are not bel ieved to have been transported from long
distances upstream.

INTRODUCTION

In 1985, the U.S. Bureau of Reclamation (USSR) conducted an
investigation of the endangered fishes of the upper Colorado River
immediately upstream of Lake Powell. The effort was concentrated in the 16-
mile reach of Cataract Canyon from the confluence of the Colorado and Green
Rivers downstream to Imperial Canyon (Fig. 1).

The primary objective of the investigation was to assess the use of the
Colorado Ri ver immedi ately above Lake Powell by the endangered Colorado
squawfish (Ptychocheilus lucius), humpback chub (Gila cypha), and bony tail
(Gila elegans). It was of special interest to determlne if Colorado
squawfish spawn in Cataract Canyon, and if those spawners originate in upper
Lake Powell. This investigation was conducted jointly with another study by
the USBR on the lake in which squawfish were previously radiotagged to
determine their movements, spawning sites, and use of this region of the
upper basin.

The USBR has had an ongoing field program on endangered fishes in upper
Lake Powell since 1980, when studies of striped bass yielded 45 large adult
Colorado squawfish near Gypsum Canyon (Persons et al. 1982; Valdez et a1.
1982). This aggregation of adults brought attention to the waters of upper
Lake Powell and to their possible importance to the endangered fishes.

Since 1980, the USBR has radiotagged and tracked adult squawfish in
upper Lake Powell to assess the impact of lake management on this endangered
species. Recent findings of larvae and young-of-the-year (yay) in the upper
lake now lead biologists to believe that squawfish may spawn in the river
immediately above the lake and use the upper lake as a nursery.

Cataract Canyon is one of the last regions of the upper Colorado River
basin to receive fisheries attention. Since the first sample effort of the
Colorado River Fisheries Project (CRFP) in September 1979, only 7 sample
trips were known prior to this study; 4 by CRFP (Valdez et a1. 1982), 2 by
ERI (Carter and Valdez 1984; Valdez 1985), and 1 by USSR. These
investigations have yielded Colorado squawfish, humpback chub, and razorback
sucker, but no bony tail were reported prior to this study.

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