7861

• UCREFRP Catalog Number: 7861
• Author: Douglas, M. E., W. L. Minckley and H. M. Tyus
• Title: Qualitative Characters, Identification of Colorado River Chubs ‎(Cyprinidae
• USFW Year: 1989
• USFW - Doc Type: Genus
• Copyright Material: YES

DOUGLAS ET AL.-COLORADO RIVER CHUBS

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UTAH

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WYOMING

COLORADO

Fig. I. Sketch map of the study area and environs, Colorado and Utah.

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gered (USFWS, 1987a), some populations (and
habitats) are still not designated for recovery
because of unresolved questions pertaining to
either identity or distinctiveness. Specific reach-
es of stream, termed "sensitive areas," are con-
sidered for protection (USFWS 1987c). Such
areas are selected by criteria such as number of
adult captures within a year, presence of ripe
females during a spawning season, and so forth,
all of which demand extreme confidence in
identification. Gila elegans, also listed as endan-
gered (USFWS, 1987b), suffers similar discrim-
ination, again because populational variation is
ill-defined and the taxonomic status of individ-
uals remains unclear. This species is now so rare
it is in danger of being declared essentially ex-
tinct in nature (Kaeding et aI., 1986). No sen-
sitive areas have been designated for G. elegans,
due both to a lack of data and to difficulty and
indecision with regard to identification (USFWS,
1987b). These factors, singly and in tandem,
confuse perceived distribution of the species and
preclude essential habitat protection.

MATERIALS AND METHODS

The study area was in the lower Yampa River,
largely within Dinosaur National Monument,
Colorado (Fig. I). The Yampa River is the larg-
est tributary of the Green River, which in turn
is the largest tributary of the Colorado River.
Fishes were captured in May and June 1987
primarily by angling (Tyus and M inckley, 1988),

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with a few taken by electrofishing. Seven qual-
itative traits were tallied for morphological re-
gions (Table I; Fig. 2) deemed important in the
diagnosis of Colorado River Gila (Minckley,
1973; Rinne, 1976; Smith et aI., 1979). Eight
quantitative characters, TL and SL, head, snout,
and caudal peduncle lengths, body and least
caudal peduncle depths, and greatest depth of
caudal peduncle, were measured to the nearest
millimeter using vernier caliper or centimeter
rule. These characters were selected for ease
and speed in recording on live fishes in the field,
as well as for their potential discrimination of
taxa. Other potentially discriminating features,
such as head-nuchal depression (Smith et aI.,
1979), were omitted due to ambiguity gener-
ated by the character among our technicians
and to the length of time required for the mea-
surement. The need to release these fishes im-
mediately precluded collection of additional or
more elaborate morphological data. Counts of
dorsal- and anal-fin rays and methods of mea-
suring followed Hubbs and Lagler (1968) ex-
cept for greatest depth of caudal peduncle (ver-
tical depth of caudal peduncle at posterior end
of anal-fin base). Species identifications were
made by WLM and HMT through use of a com-
bination of quantitative and qualitative char-
acters. All individual fish were photographed
for a permanent record (HMT files).
Qualitative characters were scored from 1-
5, with I representing the most reduced or least
apparent character state, and 5 the most ex-

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