7124 ‎(2)‎

• UCREFRP Catalog Number: 7124
• Author: McAda, C. W. and R. S. Wydoski.
• Title: Technical Papers
• USFW Year: 1980.
• USFW - Doc Type: \
• Copyright Material: YES

The Razorback Sucker, Xyrauchen texanus, in the Upper Colorado
River Basin, 1974-76
By
Charles W. McAda' and Richard S. WydoskiY
U.S. Fish and Wildlife Service
Utah Cooperative Fishery Research Unit9
Utah State University, UMC-52
Logan, Utah 84322
Abstract
The razorback sucker (Xyrauchen texanus-, which has declined in abundance in the upper Colo-
rado River primarily because of man's impact on the environment, has been recommended for
listing as "threatened" in the U.S. Department of the Interior's list of threatened or endangered
species. During the present investigation, razorback suckers were nevertheless found in rela-
tively large concentrations at two restricted locations-the mouth of the Yampa River and a
flooded gravel pit connected to the Colorado River near Grand Junction, Colorado. Razorback
suckers spawned in April and May, when water temperatures were 6 to 15 C. Estimated fecun-
dity ranged from 24,490 eggs for a fish 529 mm in total length to 76,576 for a fish 485 mm long.
Estimated ages based on scale examinations indicated that the razorback suckers collected had
completed from 4 to 9 growing seasons; all were mature. Razorback suckers from the Colorado
River were significantly larger than those of the same estimated age from the Green and Yampa
rivers, probably because water temperature was higher in the Colorado River than in the other
two streams.
The Colorado River system in the western United
States has been greatly modified during the past
century, primarily by the construction of dams for
hydroelectric power generation and irrigation. The
dams have resulted in major hydrological and eco-
logical changes in the large rivers of the basin (Dolan
et al. 1974. The river environment below the dams has
been altered in three major respects: (1) seasonal fluc-
tuations in streamflow have decreased and daily fluc-
tuations have increased, (2) summer water tem-
peratures are lower and winter water temperatures are
higher, and (3) turbidity is reduced. Modifications of
such proportions usually result in major changes in
the aquatic fauna downstream (Pearson et al. 1968;
Vanicek et al. 1970; Geen 1974-.
The dams and their alteration of the river environ-
ment are believed to be major factors in the decline of
1Present address: U.S. Fish and Wildlife Service, Colorado
River Fishery Project, 447 East Main Street, Vernal,
Utah 84078.
zPresent address: Fisheries Academy, National Fisheries
Center, Route 3, Box 49, Kearneysville, West Vir-
ginia 25430.
'The Utah Cooperative Fishery Research Unit is jointly
supported by the U.S. Fish and Wildlife Service, Utah Divi-
sion of Wildlife Resources, and Utah State University. This
study was funded by the U.S. Fish and Wildlife Service,
Contract No. 14-16-0008-1140.
four endemic Colorado River fishes: the Colorado
squawfish, Ptychocheilus lucius; the humpback chub,
Gila cypha; the bonytail chub, G. elegans; and the
razorback sucker, Xyrauchen texanus (Vanicek et al.
1970; Hinckley 1973; Holden and Stalnaker 1975h-.
The Colorado squawfish and humpback chub were
both officially designated "endangered" by the U. S.
Department of the Interior (1973-; later the bonytail
chub was proposed for designation as "endangered"
and the razorback sucker as "threatened"'jU. S. Fish
and Wildlife Service 1978-.
The fish fauna of the Colorado River basin is unique
because 74% of the native species are endemic to the
basin (Miller 1958. Most of the native large-river fish
have been eliminated from the lower basin (Hinckley
1973; however, all of the species endemic to both the
upper and lower basin still occur in the upper basin.
The expansion of water development in the upper
basin now jeopardizes the remaining habitat of the
native fish. Water from the basin is expected to play a
vital role in the extraction of energy resources (e.g., oil,
oil shale, coal, and uranium) found in this region of the
western United States. The many added demands will
probably further reduce the quality and quantity of
water in the basin.
The introduction of exotic species is also believed to
have had a detrimental impact on the native fauna
(Miller 1961. Holden and Stalnaker (1975a) recorded