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

56

Table 1. Average and maximum river depths~ associated with four
populations of Gila cypha in the Upper Colorado River.

Locale
(river mile)
Debeque Canyon
(195)
Black Rocks
(136)
Westwater Canyon
(122)
Cataract Canyon
(212) **
* measurements taken in August-September during moder-
ate post-runoff flows; depth may vary with flow stage.
** miles above Lee's Ferry; all others are miles above
Green-Colorado confluence.

Average Depth
(meters)
2.2

Maximum Depth
(meters)
4.9

5.6

18.9

5.6

18.3

15.2

28.1

The maximum depths of Black Rocks , Westwater, and Cataract represent the
deepest areas encountered in the Upper Colorado River. By comparison, maximum
river depths in August and September rarely exceed 4-5 m.

Gila cypha also appear to associate with specific substrates; large
irregular boulders or steep, sheer cliffs. The populations in Debeque and
Cataract Canyons, and partially in Black Rocks are associated with large
boulders. The boulders near Black Rocks and in Debeque Canyon are part of a
railroad or highway foundation. In Black Rocks and Westwater Canyon, the sub-
strate is typically a dark hardened gneiss rock with pockets of gravel and
sand. Gila cypha are commonly associated with the steep gneiss walls,
expecially where depressiorsand cutaways forms rooms, eddies, and pockets.

Detailed measures of depth, velocity, and substrate type are being taken
by CRFP in order to quantify habitat parameters selected by G. cypha. These
data will be incorporated into the instream flow methodology of the Western
Energy and Land Use Team of the U.S. Fish and Wildlife Service for determining
flow requirements of the species.

SYSTEMATICS

There presently remain many questions as to what constitutes the species
~ cypha, ~ elegans, and ~ robusta. Although systematic ichthyologists
generally agree that the three are separate forms, a clear delineation of the
extent of variation and hybridization requires further analyses. Such varia-
tions as sexual dimorphism, geographic and allometric differences, and habitat
requirements are not clearly distinct for each species. (Suttkus and Clenuner
1977) .

Although the majority of Gila captured in the Upper Colorado River are
clearly robusta, elegans, or cy~ some individuals exhibit overlapping