7166

• UCREFRP Catalog Number: 7166
• Author: Miller, W. H., et al.
• Title: Yampa River Fishes Study
• USFW Year: 1982.
• USFW - Doc Type: Final Report.
• Copyright Material: NO

area. Humpback chub were rare in 1981 as was reported by Holden and
Stalnaker (1975) for the 1968-71 period. Five fish were identified as
humpback in a trammel net and one was preserved for taxonomic analysis
(Table 23). The preserved specimen was assessed as a humpback-type with
some roundtail influence. Two of the six fish captured were at RM 342
(km 547) on the Green River in Whirlpool Canyon and were taken on 5
August 1981. The other four fish were captured on the Yampa River at
three different points between 23 June and 10 September 1981. Five of
the six humpback, or humpback-type, were collected with trammel nets in
eddy.or pool habitats at water depths greater than 5 ft (1.5 m) and
water velocities less than 0.5 ft/s (0.15 m/s).
Taxonomy of Gila spp. in the Colorado River system is presently in
a confused state. The endangered G. cypha and G. elegans are difficult
to identify at all life stages and this problem is compounded by sympatry
with the very similar roundtail chub (G. robusta). Adult specimens
exhibiting characteristic features of G, cypha and G. robusta are
readily identified in the field by gross morphology, However, these
features are often not well developed and are especially difficult to
observe in young and juvenile specimens. Intermediates or variants of
both species also occur.
Several criteria have been utilized to assist in the identification
of the three species of Gila in the field; fin ray counts, scale counts,
fin lengths, nuchal hump depth, eye diameter, squamation, etc. No single
criterion or set of criteria appear to readily segregate the species.
A nuchal hump development ratio was developed by Smith et al.
(1979) to assist identification of Gila spp, and hopefully eliminate the
need for many other morphological measurements that were cumbersome or
required sacrifice of the fish. The ratio PIP2/d is derived by dividing
the distance between the origin of the pelvic and pectoral fins (PIP2)
by the depth of the frontal depression (d), the depth measured from a
plane between the highest part of the nuchal hump and dorsal tip of the
snout to the bottom of the frontal depression.
A frequency distribution of nuchal hump ratios from 100 Gila spp.
captured from the Green River in 1980 and 1981 (Tyus et al. 1981) was
plotted for preliminary use. This figure indicated considerable overlap
between specimens. Problems detected during use of the nuchal hump
ratio (Smith et al. 1979) are as follows:
Ia. The method was developed from preserved specimens, not
live Gila (personal communication, G. R. Smith). Measure
ments taken during this study are from live Gila.
lb. Since it was possible that measurements may differ between
live vs. preserved fish, measurements from the same fish,
both live and preserved, were taken. Ther measurements
(PIP2 and d) differ after preservation. No consistent
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