7305

• UCREFRP Catalog Number: 7305
• Author: Tyus, H. M. and W. B. Harned.
• Title: Distribution, Spawning and Habitat Use of the Razorback Sucker in the Green River Basin, Colorado and Utah, 1979-84.
• USFW Year: 1985.
• USFW - Doc Type: \
• Copyright Material: YES

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From 1982-1984 the Colorado River Fish Monitoring Project, conducted by
the two agencies, provided more indepth studies of the Colorado squawfish.
Although not a primary target species, some data were collected for the
razorback sucker during these two projects, that provided the impetus
for a special razorback sucker spawning survey conducted from the Vernal
FWS field station in 1984. This paper presents the razorback data obtained
in the Green River Basin of Colorado and Utah from 1982-84 summarizes earlier
FWS information collected there, and contrasts these findings with the work
of others.

DISTRIBUTION AND SPAWNING

The razorback sucker is widely distributed in the mainstem Green River and
lower portions of the Duchesne and Yampa rivers. A total of 244 adult
razorback have been collected there by FWS since 1979, 152 during the present
study. The sizes of these fish range from 426 to 583 rom total length (TL),
with 23% of these less than 500 mm, 63% in the 500 - 550 mm size class,
and 15% greater than 550 mm. The center of distribution of the razorback in
the Green River (Figure 1) appears to be from Sand Wash to Split Mountain,
where they are collected in greatest numbers. The razorback was also collected
in the Duchesne River, Island and Echo parks of the Green River within Dinosaur
National Monument, and in the lower, flatwater sections of the Green River in
Labyrinth Canyon (Figure 2).

Razorbacks were most readily captured during the spring runoff period, and
Vernal FWS personnel captured 47 razorback in breeding condition (tubercles
and/or sex product) from 1981-1984. These collections have resulted in
the delineation of three suspected spawning areas: Island and Echo parks of
the Green River in Dinosaur National Monument, including the lower mile of the
Yampa River; the Jensen area of the Green River from AShley Creek to Split
Mountain; and the lower few miles of the Duchesne River. Two tuberculated
fish captured in Labyrinth Canyon of the Green River were not judged to be
significant enough to warrant inclusion of this area also (Table 1). The
Jensen area, from the mouth of Ashley Creek to Split Mountain, has produced
more ripe razorbacks than any area sampled, and 22 of the 33 razorbacks
captured with ripe sex products came from this area. Ripe male razorbacks
were smaller in average size (502 rom TL, n=13) than ripe females (541 rom,
n=ll). The male:female ratio was 1.35:1 on suspected spawning grounds.

Successful spawning of the razorback sucker in the Upper Green River was
supported by the collection of razorback larvae from riverine areas
immediately downstream of suspected spawning areas in 1984 (Figure 2). These
larvae, believed to be razorback sucker by the Larval Fish Laboratory of
Colorado State University, were identified by comparison with cultured Xyrauchen
protolarvae and mesolarvae. Approximately 31% of the 42 samples (1085
specimens) contained 33 razorback larvae. No larval collections were made
in the Labyrinth Canyon area.

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