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<br />432
<br />
<br />The Southwestern Naturalist
<br />
<br />vol. 35, no. 4
<br />
<br />could interrupt spawning movements of razor-
<br />back suckers, and stream barriers have been im-
<br />plicated as factors affecting distribution of the
<br />razorback sucker (Lanigan and Tyus, 1989).
<br />Repeated collections of "running ripe" females
<br />and visual observations of razorback suckers
<br />spawning over cobble, gravel, and sand substrates
<br />(Medel-Ulmer, 1981; Tyus, 1987; Mueller, 1989;
<br />C. McAda, pers. comm.) suggest that razorback
<br />suckers typically spawn on such substrates.
<br />Spawning of razorback suckers with increasing
<br />flows indic~tes a need for cleaned and loosened
<br />substrate. 'Iv e observed abrasions on the ventral
<br />surface of the caudal peduncle of ripe female ra-
<br />zorback suckers and presumed this was due to
<br />substrate preparation prior to egg deposition. This
<br />behavior has also been observed for bluehead
<br />suckers (Maddux and Kepner, 1988).
<br />Some razorback suckers exhibited a fidelity to
<br />a specific spawning riffle as indicated by repeated
<br />capture of some fish in the same riffle (cobble-
<br />gravel-sand bar) and documented movement of
<br />some fish to a particular riffle in different years.
<br />One ripe male razorback sucker captured in the
<br />lower Yampa River (km 0.16) in 1981 was re-
<br />captured in the exact location in 1988 (also ripe).
<br />This behavior was remarkable because the fish
<br />overwintered in the Jensen area in 1987 (R. Val-
<br />dez and W. Masslich, pers. comm.) and bypassed
<br />the Jensen spawning site enroute (52.8 km) to
<br />the lower Yampa River. Use of specific spawning
<br />areas by individual fish suggests that more than
<br />one stock of razorback sucker occurs in the Green
<br />River basin. If razorback suckers in the Green
<br />River system home to specific spawning reaches,
<br />as in somu other catostomids (Werner, 1979),
<br />then reintroduction efforts should consider the
<br />need to maintain separate genetic strains.
<br />Recaptures of ripe razorback suckers in widely
<br />different habitats and river reaches within and
<br />between years may be attributed to many factors,
<br />including migration of some individuals that pass
<br />through one spawning area enroute to another,
<br />effects of electrofishing, spawning in more than
<br />one area, or non-annual spawning. It is possible
<br />that some fish attempt movements to historic
<br />spawning sites that no longer exist. The longevity
<br />of razorback suckers of perhaps 40 years (Mc-
<br />Carthy and Minckley, 1987) must be considered
<br />in evaluating spawning behavior of relict fish
<br />populations.
<br />We noted a 4- to 5-week temporal and spatial
<br />overlap in spawning of razorback, flannelmouth,
<br />
<br />and bluehead suckers, although this was not
<br />widely observed during the higher water period
<br />1984 to 1986 (Tyus, 1987). Numerous observa-
<br />tions of putative razorback sucker x flannel-
<br />mouth sucker intermediates in the upper Green
<br />and lower Yampa rivers (Hubbs and Miller, 1953;
<br />Banks, 1964; Vanicek et a1., 1970; Holden and
<br />Stalnaker, 1975b; Seethaler et a1., 1979, E. Wick
<br />and C. McAda, pers. comm.) suggest that the
<br />incidence of hybridization and introgression may
<br />be enhanced by the abundance of flannelmouth
<br />suckers, the paucity of razorback suckers, and
<br />temporal and spatial overlap in their spawning.
<br />Effects of natural and induced hybridization on
<br />the decline of the razorback sucker are not well
<br />understood (but see Buth et a1., 1987, for lower
<br />Colorado River basin fish) and need further study.
<br />Razorback suckers in the Green River basin
<br />constitute the largest group of reproducing adults
<br />in a lotic environment. However, they are pre-
<br />sumably old individuals (Tyus, 1987; W. L.
<br />Minckley, pers. comm.) and relatively few in
<br />number (Lanigan and Tyus, 1989). The low
<br />number of reproducing adults and lack of wide-
<br />spread recruitment (Holden, 1978; Wick et a1.,
<br />1982; Minckley, 1983; Tyus, 1987; Marsh and
<br />Minckley, 1989; C. McAda, pers. comm.) may
<br />be due to habitat alteration and loss (e.g., cur-
<br />tailment of spring flooding, loss of historic flow
<br />and temperature regimens, and reduced flooding
<br />of bottomlands) and predation by non-native fish-
<br />es (Minckley, 1983; Brooks et a1., 1985; Tyus,
<br />1987; Marsh and Brooks, 1989). These factors
<br />should be addressed in recovery efforts for ra-
<br />zorback sucker, as should the incidence and con-
<br />sequences of hybridization with other catosto-
<br />mids. Decline of the razorback sucker toward
<br />extinction emphasizes the need for more imme-
<br />diate measures toward its recovery.
<br />
<br />This study was funded in part by the Bureau of
<br />Reclamation and United States Fish and Wildlife Ser-
<br />vice. M. G. Hughes was among the many personnel
<br />who aided in collecting field data. We thank S. J.
<br />Cranney (Utah Division of Wildlife Resources) for
<br />providing tagging and recapture information, R. Val-
<br />dez and W. Masslich (BIOWEST, Incorporated) for
<br />providing radiotracking and tagging information, and
<br />G. Smith (United States Fish and Wildlife Service,
<br />Denver) for providing thermograph data. K. Bestgen
<br />and two anonymous reviewers improved an earlier draft
<br />of the manuscript.
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<br />J
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