8087

• UCREFRP Catalog Number: 8087
• Author: Valdez, R. A. and B. R. Cowdell.
• Title: Lake Powell Inflow Study. Annual Summary Report - 1994.
• USFW Year: 1994.
• USFW - Doc Type: 453-1,
• Copyright Material: NO

I .i
'"
"
j
I
Ii
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I

~
~

I
I
j

1.0 INTRODUCTION

This document is the Annual Summary Report for 1994 submitted to the National Park Service and Utah
Division of Wildlife Resources (UDWR) in partial fulfillment of UDWR Contract No. 90-2558 entitled Lake
Powell Inflow Studv: Transport of Age-O Colorado SQuawfish During Sprint:! Runoff. This report presents data
from the second year of this two year study. The Annual Summary Report for 1993 (Valdez and Cowdell
1994) is similar to this report. This annual report is available from BIO/WEST or UDWR in Salt Lake City,
UT. A final report, synthesizing the two years of data, will be completed in March 1995.

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 squawtish (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 transported
annually into Lake Powell.

2.

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

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 squawtish.

1.2 BACKGROUND

Mortality factors affecting age-O Colorado squawtish 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 Cowdell 1992.1993). One possible explanation for this decrease in density is
Wt age-O squawfish emigrate or are transported to orher 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 transported
downsueam by periodic high flow events during summer months (Valdez 1990).

Since Colorado squawfish once ranged throughout the Colorado River Basin, it is reasonable to suspect that
age..o Colorado squawfish actively or passively disperse downsueam 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 downsueam dispersal of younger fish to warmer reaches with temperatures more
suitable for growth and other physiologic processes. However. this downstream dispersaJ or transport today
may be blocked by Lake Powell with its limited nursery habitat and large number of predators.

The Colorado River in1low at Lake Powell has been a very dynamic aquatic environment since the oompletion
of Glen Canyon Dam in 1963. FIShery investigation of the in1low were conducted in 1979-82 (Valdez el aI.
1982), 1983-84 (B. Williams, personal oommuniCltion.), and 1985-92 (Valdez 1990. Valdez and MassUch 1991,
Valdez and Cowde1l1992.1993). These investigations have revealed variable numbers of endangered Colorado

1