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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Dorsal - Anal Fin Ray Counts

A key char~cter often used to distinguish ~ cypha from ~ robusta is
the presence of 9 dorsal and 10 anal fin rays in the former and 9 dorsal and
9 anal fin rays in the later (Holden and Stalnaker 1970, Minkley 1973). These
studies and others (Suttkus and Clemmer 1977) since have revealed great varia-
tion in this character among fish distinctly ~ cypha. Preliminary results of
the CRFP data confirm this variation in fin rays. Variation among individuals
from the same area and between individuals from separated areas indicate that
dorsal and anal fin ray counts do not appear to be a reliable single meristic
character for separation between ~ ~ and ~ robusta.

Nuchal Depth

Nuchal depth development has been suggested as an effective means of
distinguishing adults of the three Colorado River chubs (Smith, Miller, and
Sable 1979). The methodology provides a direct repeatable measurement,
accurate to 0.1 rom, of the development of the nuchal hump in association
with the depressed (often concave) dorsal surface of the skull.

A ratio is employed that is derived by measuring the depth of the frontal
depression (maximum distance between a straight line from highest part of
nuchal hump and dorsal tip of snout, and dorsal surface of skull) and
dividing this figure into the distance between the insertion of the pectoral
and pelvic fins.

This method is being used by CRFP on individuals distinctly ~ cypha
or ~ robusta as well as the apparent variants or integrades. There is
general agreement between the nuchal hump ratios presented by Smith, Miller
and Sable (1979) and those preliminarily computed for individuals from three
of the four populations of the Upper Colorado River (Black Rocks, Westwater,
and Cataract). Measurements on individuals from the Debeque population
generally lie outside of the nuchal hump ratios established for ~ cypha.

Taxonomic Analyses

Taxonomic and systematic studies are being conducted on young, juveniles,
and adults of G. cypha, robusta, and elegans. Analyses of young and juveniles
are being conducted by Dr. Daryll Snyder at the LarVal Fishes Laboratory in
Fort Collins, Colorado. A guide to the larval fishes of the Colorado River
will be the p~oduct of this work. Adults are being examined by Drs. Royal
Suttkus and Glenn Clemmer in affiliation with the Denver Wildlife Research
Center of the U.S. Fish and Wildlife Service. Drs. Suttkusand Clemmer are
examining specimens from past and present collections to establish the breadth
of variability exhibited by each of the three Gila forms.

SUMMARY

The humpback chub of the Upper Colorado River is distributed in four
areas (1) Debeque Canyon, Colorado (verification of identity pending) (2)
Black Rocks, Colorado (3) t~estwater Canyon, Utah and (4) Cataract Canyon, Utah.
Ongoing studies by the Colorado River Fisheries Project indicate that deep, swift,
rock canyons are critical to the survival of the species.