9583

• UCREFRP Catalog Number: 9583
• Author: BIO/WEST Inc.
• Title: Annual Summary Report 1993 - Survival of Age-0 Colorado Squawfish in the Green and Colorado Rivers ‎(UDWR Contract No. 90-2558)‎.
• USFW Year: 1994.
• USFW - Doc Type: Logan, UT.
• Copyright Material: NO

1.0 INTRODUCTION
This document is the Annual Summary Report for 1993 submitted to the Utah Division of Wildlife Resource
in partial fulSllment of Contract No. 90-2558 entitled Endangered Fish Studies of the Lower Green and
Colorado Rivers, Cataract Canyon, and Lake Powell Inflow. This investigation represents the ninth 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 - 1992
(Valdez and Masslich 1990,1991; Valdez and Cowdell 1992,1993) 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-0 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 responstbility 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 (Ptychocheilus 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. Squawflsh typically
spawn July through August when water temperatures reach 18-22°C (Vanicek and Kramer 1969, Holden and
' Stalnaker 1975, Seethaler 1978). Incubation time is usually 3-4 days (Hammon 1981), and newly hatched
larvae can be transported by river currents for varying distances downstream to nursery habitats ('I'yus and
Haines 1991, Valdez 1990). Age-0 squawfish are abundant in backwaters sampled during late summer and fall
on the Green and Colorado rivers above their confluence (Holden and Stalnaker 1975, Valdez 1990, Tyus and
Haines 1991).
Little is known about survival ofage-0 Colorado squawftsh. 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-0 squawfish in backwaters sampled during June and July. Increased concern over recruitment of age-0
' 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-0 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-0 Colorado squawfish. These
hypotheses are:
Ho 1: Age-0 squawfish use habitats unavailable to conventional seining methods.
' Ho 2: Age-0 squaw6sh move or are transported into and from the region.
' Ho 3: Ovetwinter mortality contributes to decreases of age-0 squawfish.

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