7055

• UCREFRP Catalog Number: 7055
• Author: Archer, D. L., L. R. Kaeding and B. D. Burdick.
• Title: A Study of the Endangered Fishes of the Upper Colorado River.
• USFW Year: 1985.
• USFW - Doc Type: Grand Junction, Colorado.
• Copyright Material: NO

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COLORADO SQUAWFISH INVESTIGATIONS

Introduction

Colorado squa~fish, formerly the major piscavore of the Colorado River
basin, ~as historically distributed throughout the large rivers of the basin.
However, because of habitat modification, the introduction of exotic fishes
and other adverse changes in its environment, they no~ occur only in the upper
basin in Utah and Colorado--about 25' of its original range (Tyus et ,a1.
1982a, Tyus 1984). Although early ~hite settlers believed Colorado squawfish
undertook spawning migrations, evidence that supports such speculation was not
collected until recently. Holden and Stalnaker (1975b) and Seethaler (1978)
reported that the numbers of adult Colorado squawfish in the lower Yampa River
increased during late summer, apparently because the fish moved from the Green
River into the Vampa to spawn. Spawning migrations of more than 100 mi were
subsequently reported in the Vampa and Green rivers, as was long-distance
movement of squawfish from the White River to spawning areas in the Green and
lower Vampa rivers (MH11er et a1. 1983).

Because demands for upper Colorado River basin water might further alter
the river ecosystem, concern has arisen that additional water development
might eliminate Colorado squawfish. Particular concern was expressed for the
loss of spa~ning areas and the attendant reduction in reproductive success.
For example, some potential developments include dams that might block the
migration of adult Colorado squawfish to spa~ning areas and thereby adversely
affect reprOduction, much like dams have affected anadromous salmon
(Onchorhvchus spp. and Salmo salar). Other developments might eliminate
spawning areas directly, perhaps because of adverse changes in temperature,
dewatering, or the enhancement of undesirable fishes. Accordingly, the
objectives of the present study were: (1) to describe the seasonal movement
patterns of adult. Colorado squa~fish in the upper Colorado River and the
relationships between such movement and the occurrence of spa~ning areas; and
(2) to estimate the annual reprOductive success of Colorado squawfish in the
upper Colorado River and identify the factors that affect reproductive
success. These objectives relate directly to objeclives 1, 2, 3 and 6, as
described on page 7 of this document.

Study Area

The study area consisted of the 2OD-mi reach of the Colorado River
between the upstream region of Lake Powell, Utah, and the City of Palisade,
Colorado (Figure 1). Locations along the river are identified on the basis of
river-mile distance upstream from the confluence with the Green (River Mile
[RMl 0) according to maps provided in Belknap and Belknap (1978). Locations
below the conf1uence--in Cataract Canyon and upper lake Powell--are identified
as river miles upstream from lee Ferry (e.g., Hite Marina, RM 168; confluence
with Green River, RM 216).

We divided the study area into four reaches; reaches 1 and 2 and reaches
3 and 4 are separated by areas of major rapids--westwater and Cataract canyons
(Figure 1). River reaches in these canyons are not easily accessable and
therefore were not routinely sampled as part of the present study. Reach 4, the
upper reach (RM 110-185), consisted of the moderate-gradient region in the Grand

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