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

in the summer than that represented by USFWS.

Of the 152 YOY squawfish captured within Cataract Canyon, 63.16% were
caught in the area of Cataract Lake, a relatively calm 4-mile reach of river
(Fig. 3). Only 19.08 and 17.76% of the YOY were taken above the rapids and
in the upper rapids, res~ectivelY. However, CPE was highest in the upper
rapids with 1.41 YOY/10m. No YOY squawfish were found in the lower, more
severe rapids, where the average gradient is 38 feet per mile.

The distribution pattern of YOY squawfish seen in this study suggests
that, in 1985, reproduction of this species occurred primarily in the Green
River. However, since the dispersal of YOY squawfish by river flows is not
known, three hypotheses a re presented as to the ori gin of these fi sh in
Cataract Canyon and upper Lake Powell:

1. They were transported for long distances downstream from known and
suspected spawning sites in the Yampa, upper Green, and upper
Co 1 orado Ri vers ,

2. They were transported from unknown spawning sites in the Colorado
and Green Rivers in the 50 miles above the confluence, and

3. They originated from unknown spawning sites in Cataract Canyon and
upper Lake Powell.

As a way of addressing these hypotheses, drift netting is recommended
for future studies immediately above the confluence to assess the relative
contribution of YOY squawfish from the Colorado and Green Rivers into
Cataract Canyon. Additional dri'ft netting is recommended at upper Lake
Powell to assess transport of YOY into that body of water.

Hatching Times. To gain additional knowledge on the ongln of these
YOY, hatching dates were computed from relationships developed by Haynes et
ale (1985) and plotted on a frequency histogram (Fig. 4). From this
analysis, it is evident that in 1985, hatching of Colorado squawfish,
captured within the Cataract Canyon study area, occurred over a period of
time. Some of the variation seen in Figure 4 is attributed to differential
growth rates or sl ight errors in length measurements afield. However, the
majority of observations indicate that hatching began in late June, peaked
on July 1, and continued through the first of August. A correction factor
of 3-5 days can be appl ied to the predicted hatching dates to represent
predicted spawning dates, since Hamman (1981) reported incubation time for
Colorado squawfish of 90-121 hours at water temperatures of 20-24 C.

In order to identify the origin of these YOY, hatching times are
compared for the fish captured in this study area with those computed for
squawfish from other parts of the upper basin. Although 1985 data for yay
squawfish from other regions are not available at the time of this writing,
a comparison of the data from Cataract Canyon is made with predicted
hatching dates for squawfish of the Yampa River for 1983 and 1984 (Haynes et
ale 1985). Assuming that the 1983-84 data span the normal hatching times
for the species in the Yampa River (mid to late July and early August), it
is hypothesized that squawfish found in Cataract Canyon hatch earlier (early
July) because of earlier warming lower in the subbasin.

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