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<br />THE SOUTHWESTERN NATURALIST 35(4):427-433
<br />
<br />DECEMBER 1990
<br />
<br />SPAWNING AND MOVEMENTS OF RAZORBACK
<br />SUCKER, XYRAUCHEN TEXANUSJ IN
<br />THE GREEN RIVER BASIN OF
<br />COLORADO AND UTAH
<br />
<br />HAROLD M. TyUS AND CATHERINE A. KARP
<br />
<br />United States Fish and Wildlife Service,
<br />1680 West Highway 40, Number 1210,
<br />Vernal, UT 84078
<br />
<br />ABSTRACT-Spawning and movements of the razorback sucker, Xyrauchen texanus, were evaluated
<br />by radiotelemetry (n = 17 fish) and capture of 230 adults (105 recaptures) in the Green and Yampa
<br />rivers, 1987 to 1989. Ripe fish (n = 194) were captured in riffles with cobble, gravel, and sand
<br />substrates from mid-April to early June. Recaptured males were ripe from 2 to 28 days and recaptured
<br />females from 2 to 15 days. Razorback suckers spawned during ascending and highest spring flows at
<br />water temperatures of about 140C (range of 9 to 170C). Spawning migrations of 30 to 106 kIn were
<br />detected in 17 razorback suckers, but movements were more limited or undetected in other individuals.
<br />Flooded lowlands and lower portions of tributary streams presumably served as resting-feeding areas
<br />for razorback suckers during the breeding season. Native flannelmouth sucker (Catostomus latipinnis),
<br />bluehead sucker (Catostomus discobolus), and putative flannelmouth x razorback sucker hybrids in
<br />breeding condition were collected with ripe razorback suckers. Razorback sucker is in peril due to a
<br />paucity of spawning adults, hybridization with other suckers, little or no recruitment, and habitat
<br />loss.
<br />
<br />The razorback sucker, Xyrauchen texanus, is
<br />one of several catostomid fishes endemic to the
<br />Colorado River basin. This monotypic genus, once
<br />so abundant that it was harvested as a commercial
<br />food Uordan, 1891; Hubbs and Miller, 1953;
<br />Miller, 1961; Minckley, 1973, 1983; Moyle,
<br />1976), is now threatened with extinction (Wick
<br />et aI., 1982; Minckley, 1983; Tyus, 1987). Ra-
<br />zorback sucker is proposed for listing under pro-
<br />visions of the Endangered Species Act of 1973
<br />and is protected by the states of Arizona, Cali-
<br />fornia, Colorado, Nevada, Utah, and Wyoming
<br />(United States Department ofthe Interior, 1990).
<br />Natural populations of razorback suckers exist
<br />only in some reservoirs in the lower Colorado
<br />River (Minckley, 1983; Marsh and Minckley,
<br />1989), in the upper Colorado River near Grand
<br />Junction, Colorado (Wick et al., 1982), sporad-
<br />ically in the lower San Juan River (M. Moretti,
<br />pers. comm.), and in the Green and Yampa rivers
<br />of Utah and Colorado (Vanicek et al., 1970;
<br />Holden and Stalnaker, 1975a, 1975b;Tyus, 1987).
<br />Although small, the last population represents the
<br />
<br />largest extant riverine population of this species
<br />(Tyus, 1987; Lanigan and Tyus, 1989). Razor-
<br />back sucker stocks are composed of old individuals
<br />and recruitment is minimal or nonexistent
<br />throughout the Colorado River basin (McCarthy
<br />and Minckley, 1987; Tyus, 1987; Marsh and
<br />Minckley, 1989).
<br />Distribution, abundance, and habitat use of
<br />razorback sucker in the Green River basin has
<br />been studied by various investigators (Wick et aI.,
<br />1982; Tyus, 1987; Lanigan and Tyus, 1989; C.
<br />McAda, pers. comm.). We further describe
<br />spawning, movements, and habitat use of razor-
<br />back sucker relative to discharge and temperature
<br />regimens and provide information about associ-
<br />ated species to further recovery efforts for this
<br />fish.
<br />
<br />MATERIALS AND METHODs-Razorback suckers
<br />were collected by electrofishing in the upper Green
<br />River (km 396.8 to 552.0) on 20 April to 4 June 1987,
<br />25 April to 2 June 1988, and 20 April to 7 June 1989
<br />and in the lower Yampa River (km 0 to 4) on 21 May
<br />1987, 12 May to 2 June 1988, and 20 April to 30 May
<br />
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