8003

• UCREFRP Catalog Number: 8003
• Author: Haynes, C. M. and R. T. Muth.
• Title: Identification of Habitat Requirements and Limiting Factors for Colorado Squawfish and Humpback Chubs ‎(January 1, 1981 to June 30, 1982)‎.
• USFW Year: 1982.
• USFW - Doc Type: SE-3-4,
• Copyright Material: NO

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no measurable velocity. Six individuals were associated with a predominantly I
silt substrate, while the remaining seven were found over sand. Depths (`
ranged from 0.2 - 1.3 meters.
A long-term analysis (1979-1983) of the possible relationships of YOY
distribution and abundance with physical habitat variables (i.e. seasonal
flow and temperature patterns) is being conducted and this analysis will
be included in the final report.
Gila spp.
To date, reliable criteria for differentiation of YOY humpbacks, roundtails,
and bonytails do not exist. Collections of larval and juvenile chubs have
been made in both study areas and, although the specimens are probably
predominantly roundtails, stored specimens are classified as Gila spp.
It is anticipated that morphomeristic analysis of known-age hatchery larvae
of bonytails and various genetic crosses will be completed during winter-
spring of 1983. Multivariate statistical analyses of "knowns" will be
employed to determine those features, if any, which may be used to distinguish
the species, afterwhich unknown field-collected specimens will be compared.
Tables D-1 and D-2 summarize morphomeristic analysis of hatchery-reared
humpbacks (Little Colorado River and Black Rocks stock, respectively.
Spinal deformities (lordosis) in YOY chubs were observed during 1981
August Yampa River collections. ~In 1981, 101 of 127 samples (79.5%)
contained deformed chubs. A total of 4032 specimens were examined, of which
667 (16.5%) were deformed. A subsequent inspection of August 1980 Yampa
samples revealed deformed chubs in 68 of 106 samples (64.1%). A total
of 3497 YOY chubs oras examined of which 360 (10.3%) were deformed. For
1981, YOY chubs ranged from 14.5 - 48.0 mm TL and were probably 17-84 days
old. Deformed specimens were 23.0 - 41.0 mm TL suggesting that spinal
curvature appeared at 34-70 days. A number of yearlings (> 48 mm TL) were
collected, but lordosis was not observed in this group. Examination of
cleared and stained whole specimens indicates a gradual spinal curvature
beginning near the 10th trunk vertebra through the 11th caudal. Maximum
ventral depression was at the 3rd and 4th caudal. Vertebral rupture,
separation, or compression were not evident. Microscopic examination of
saggital series has not revealed any readily noticable gross differences
between deformed and normal fish. Examinations for two parasites known
to be associated with fish spinal deformities (Myxosoma cerebralis and
Ichthyosporidium hoferi) were negative. At this time, neither cause-effect
nor impact upon Yampa River chubs can be determined; however, it is likely
that such deformities, unless reversible, reduce the fitness of individuals
relative to feeding, predator escape, etc. A number of factors have
been shown to cause lordosis, including water quality, genetics, radiation,
and electric current. Based upon spinal deformities observed in wild
populations of salmonids, pike, and herring--none of which had frequencies
as high as Yampa River chubs--Bengston (1979) proposed using the frequency
of deformities as a monitor of marine pollution.
An evaluation of frequency of deformities in 1982 collections will be made
as samples are processed.