8086

• UCREFRP Catalog Number: 8086
• Author: Valdez, R. A. and B. R. Cowdell.
• Title: Lake Powell Inflow Study. Annual Summary Report - 1993.
• USFW Year: 1994.
• USFW - Doc Type: 384-1,
• Copyright Material: NO

I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I

1.0 INTRODUCTION

This document is the Annual Summary Repon for 1993 submitted to the National Park Service and Utah
Division of Wildlife Resources in partial fulfillment of UDWR Contract No. 90-2558 entitled Lake Powell
Inflow Study: Transport of Age-O Colorado Squawfish During Spring Runoff. This report presents data from
the first year of this two year study.

1.1 PURPOSE AND OBJECTIVES

The purpose of this investigation is to monitor the Lake Powell inflow of the Colorado River before and after
spring runoff to determine if significant numbers of age-O Colorado squawfish (Ptvchocheilus lucius) and larval
razorback suckers (Xvrauchen texanus) are being transported into the area. The objectives of this study are
to:

1. Determine the number of age-O Colorado squawfish and larval razorback suckers transponed
llllJlually into Lake Powell.

2. Assess the relationship between spring runoff level and numbers of fish transponed.

3. Assess the level of predation on age-O Colorado squawfish by lake-dwelling species.

4. Recommend management strategies to increase survival of age-O Colorado squawfish.

1.2 BACKGROUND

Mortality factors affecting age-O Colorado squawfish in the upper Colorado River basin are not well
understood. Although successful reproduction occurs annually, the densities of age-O at the end of their first
three months of life are substantially reduced by the time the fish are one year of age (Valdez 1990, Valdez
and Masslich 1991, Valdez and CowdeIl1992,1993). One possible explanation for this decrease in density is
that age-O squawfish emigrate or are transported to other regions of the river. Recent findings indicate that
age-O Colorado squawfish from nursery areas in the lower Green River (RM 50 - 0) may be transponed
downstream by periodic high flow events during summer months (Valdez 1990).

Since Colorado squawflsh once ranged throughout the Colorado River Basin, it is reasonable to suspect that
age-O Colorado squawflSh actively or passively disperse downstream during spring runoff. Thompson (1989)
reponed that growth rates and survival of age-O squawfish are adversely affected by cold water temperatures.
Kaeding and Osmundson (1988) hypothesized that temperature regimes in the Upper Colorado River Basin
are sub-optimal for growth of age-O Colorado squawfish, resulting in increased early-life mortality and
subsequent decline in numbers in the upper basin. The apparent rigors of low temperatures on young
Colorado squawfish, in addition to the possibility of sub-optimum temperatures in the Upper Basin, suggest
adaptive advantages for downstream dispersal of younger fish to warmer reaches with temperatures more
suitable for growth and other physiologic processes. However, this downstream dispersal or transpon today
may be blocked by Lake Powell with its limited nursery habitat and large number of predators.

The Colorado River inflow at Lake Powell has been a very dynamic aquatic environment since the completion
of Glen Canyon Dam in 1963. Fishery investigation of the inflow were conducted in 1979-82 (Valdez et at.
1982), 1983-84 (B. Williams, personal communication), and 1985-92 (Valdez 1990, Valdez and Masslich 1991,
Valdez and Cowdell1992,1993). These investigations have revealed variable numbers of endangered Colorado
River fishes, including Colorado squawfish, razorback suckers and humpback chub (Gila mlW.

1