8185

• UCREFRP Catalog Number: 8185
• Author: Valdez, R. A. and B. R. Cowdell.
• Title: Annual Summary Report-1992\
• USFW Year: 1993.
• Copyright Material: NO

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1.0 INTRODUCTION

This document is the Annual Summary Report for 1992 submitted to the Utah Division of Wildlife Resource
in partial fulfillment of Contract No. 90-2558 entitled Endangered Fish Studies of the Lower Green and
Colorado Rivers. Cataract Canvon. and Lake Powell Inflow. This investigation represents the eighth year of
studies by BIO/WEST, Inc. in this region of the Upper Colorado River Basin that began in 1985. Prior to
1990, these investigations were supported by the Bureau of Reclamation (Reclamation). Annual Summary
Reports were submitted for each of the first three years (Valdez 1985, Valdez 1987, 1988), and a Final Report
(Valdez 1990) summarized the results from 1985 through 1988. Annual Summary Reports for 1989 - 1991
(Valdez and Masslich 1990,1991; Valdez and Cowdell1992) are similar to this report. These annual reports
and trip progress reports are available from BIO/WEST or UDWR in Salt Lake City, UT.

1.1 OBJECTIVES

The objectives of this investigation were to assess survival of age-O Colorado squawfish and assist the
Interagency Standardized Monitoring Program (ISMP, U.S. Fish and Wildlife Service 1987).

1.2 BACKGROUND

This investigation was conducted as part of UDWR's Native Species Program on endangered fishes of the
Upper Colorado River Basin. That program is part of the responsibility of states, under the Wildlife
Coordination Act and the Endangered Species Act of 1973, as amended, to protect and, where possible,
promote the recovery of these fishes.

The Colorado squawfish (Ptvchocheilus lucius) is a large piscivorous cyprinid native to the Colorado River
Basin, and listed a federally endangered species by the U.S. Fish and Wildlife Service. Squawfish typically
spawn in July or August when water temperatures reach 18-220C. Incubation time is usually only 5 days, and
newly hatched larvae can be transported by river currents for varying distances downstream to nursery habitats.
Age-O squawfish are abundant in backwaters sampled during late summer and fall on the Green and Colorado
rivers above their confluence.

Little is known about survival of age-O Colorado squawfish. Kaeding et al. (1985) hypothesized that high early-
life mortality might be an important factor limiting Colorado squawfish populations in the upper basin.
Research at that time on the Green and Colorado rivers by Valdez (1985,1986) revealed relatively low numbers
of age-O squawfish in backwaters sampled during June and July. Increased concern over recruitment of age-O
squawfish coupled with data suggesting high over-winter losses, prompted additional sampling of the Green
and Colorado Rivers above their confluence. Systematic monitoring of age-O squawfish, consistent with the
ISMP, was incorporated into the Cataract Canyon Studies in 1987. This ongoing program was designed to test
three hypothesis associated with apparent over-winter decreases in age-O Colorado squawfish. These
hypotheses are:

Ho 1: Age-O Colorado squawfish use habitats unavailable to conventional seining methods.

Ho 2: Age-O Colorado squawfish move or are transported downstream into and from the study
region.

Ho 3: Age-O Colorado squawfish are lost to overwinter mortality from starvation, diseases, parasites,
etc.

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