7340

• UCREFRP Catalog Number: 7340
• Author: Valdez, R. A.
• Title: Status of the Distribution and Taxonomy of the Humpback Chub,
• USFW Year: 1980
• Copyright Material: YES

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Colorado, and Lake Powell, Utah. This presentation encompasses that portion
of the investigation conducted on the 450 kIn of the Upper Colorado River.

DISTRIBUTION

The Humpback Chub Recovery Plan (Colorado River Fishes Recovery Team 1979)
identifies five areas in the Colorado River in which Q. cypha is presently
distributed (Figure 1). Included in the Upper Colorado River is an 80-km
stretch of river between Palisade and Black Rocks, Colorado. That area includes
one distinct population in Black Rocks, Colorado (Kidd 1977) about 6 km upstream
from the Utah line, and a suspected population near Palisade, Colorado (Kidd,
personal communication), 94 km further upstream.

The CRFP has continued to monitor the Black Rocks population, and specifi-
cally located the population near Palisade in an area of Debeque Canyon (Figure
1). However these individual lack the pronounced morphological features of the
species and systematic studies are being conducted to verify their identity.
A second new population was discovered October 9, 1979, in Westwater Canyon,
Utah, about 11 km downstream from the Colorado state line. IndiV-Wualcatches
of Q. cypha in Cataract Canyon, Utah, 210 kIn further downstream, indicate the
existence of a third new population in the Upper Colorado River. Verifying the
Cataract population may be difficult because o~ severe rapids and swift water.
The few individuals caught in Cataract Canyon (1 adult and several juveniles)
may be remnants of a population reported from Lake Powell shortly after im-
poundment in the 1960's (Colorado River Fishes Recovery Team 1979) .

The size and extension of each population has not been ascertained but
tagging studies indicate that individuals of the Black Rocks population remain
within a 2-3 kIn section of river. Similar ranges are predicted for the other
three populations. This apparent lack of extensive movement may be a function
of unique habitat, as discussed in the following section.

GENERAL HABITAT PREFERENCES

The four recognized populations of Q. cypha in the Upper Colorado River
are distinctly associated with the deeper and swifter riverine areas. In
Debeque Canyon, for example, G. cypha are concentrated in an area with an
average river depth of 2.2 m and a maximum of 4.9 m (Table 1). The Black Rocks
and Westwater populations inhabit areas surprisingly similar in average (5.6 m)
and maximum depth (18 m). The deepest area encountered in the Upper Colorado
River is below Brown Betty Rapid in Cataract Canyon, with a maximum depth of
28.1 m and an average of 15.2 m. Humpback chubs were captured near this area.