7337

• UCREFRP Catalog Number: 7337
• Author: Valdez, R. A., R. J. Ryel and R. Williams.
• Title: Endangered Fishes of Cataract Canyon
• USFW Year: 1986.
• USFW - Doc Type: The Importance of the Colorado River above Lake Powell to the Colorado Squawfish, Humpback Chub, and Bonytail.
• Copyright Material: NO

RESULTS

Summary Of Fish Collections

A total of 22 species of fishes, representing 11 families, were handled
during this investigation (Table 1). As a percentage of total catch for the
region of the lower Green, Cataract Canyon, and upper Lake Powell, the most
common species caught were red shiner (57.73%), channel catfish (20.52%),
and common carp (11.26%). These three introduced species made up 89.51% of
the total catch.

Of the 22 flsh species recorded, 15 are introduced and only 7 are
native. As a percentage of total catch, the ratio of introduced to native
species was 96.7 to 3.3. The endangered species (Colorado squawfish, 1.97%;
humpback chub, 0.04%; and bony tail, 0.01%) made up 2.02% of the total catch.
Razorback sucker (Xyrauchen texanus) were not captured during this
investigation.

Fish species composition of Cataract Canyon differed considerably from
that of the surrounding region, primarily because of the influence of fishes
from Lake Powell. This influence increases the proportion of introduced,
species that were not encountered in Cataract Canyon, i.e. walleye, striped
bass, threadfin shad, black crappie, kokanee salmon, northern pike.

Within Cataract Canyon, there were 16 species handled, including 9
introduced and 7 native (Table 1). In the Canyon, red shiners were most
abundant with 37.61% of the catch, followed by carp (19.94%) and channel
catfish (19.21%) for a total of 76.76%. Thus, these three introduced fishes
dominated the fish population of both Cataract Canyon and the region of the
upper basin.

Colorado Squawfish

A total of 517 Colorado squawfish were captured during the six trips,
including 4 adults, 3 juveniles, 509 YOY, and 1 emaciated fish that was not
classified by age group. These fish were captured from RM 41.8 on the Green
River downstream to RM 199.6 near Imperial Canyon in upper Lake Powell.
Three of the four adults and all three juveniles were captured within
Cataract Canyon between RM 206.5 and 213.9. One adult was caught in upper
Lake Powell at RM 201.2.

Distribution Of YOY. Of the 509 YOY squawfish handled, 67.78% came
from the Green River within 41.8 miles of its confluence with the Colorado
River, while 29.86% came from Cataract Canyon (RM 216.5-201.0), and only
2.36% came from upper Lake Powell (RM 201.0-196.5) (Fig. 2). Since sampling
in each of the three regions differed in intensity, catch per unit effort
(~PE) is presented for a more comparative analysis. CPE was 4.30 YOY per 10
m in "the Green River, 0.82 in Cataract Canyon, and 0.09 in upper Lake
Powell. The Colorado Ri ver above the conf1 uence was not sampl ed since YOY
sampl ing was being conducted by the USFWS. CPE for the lower 40 miles of
the Green River (4.30) was higher than recorded by Archer a~d Tyus (1984) of
USFWS, who presented a mean CPE of about 1. 7 YOY per 10 m for the peri od
1979-1982. This investigation may have yielded a higher CPE because of
annual variation in fish density or because sampl ing was conducted earl ier

4