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<br />390
<br />
<br />The Southwestern Naturalist
<br />
<br />vol. 39, no, 4
<br />
<br />depth at point of capture was 0,1 to 0,2 m, Surface
<br />water temperature was 340C, Other fishes col-
<br />lected included four common carp (Cyprinus car-
<br />Pio), 97 red shiners (Cyprinella lutrensis), 30 fat-
<br />head minnows (Pimephales promelas), 10 sand
<br />shiners (Notropis stramineus), 37 channel catfish
<br />(/ctalurus punctatus), and two green sunfish (Le-
<br />pomis cyanellus),
<br />Several biologists have suggested that our cap-
<br />tures might be escapees from an experimental
<br />culture facility at the Ouray National Wildlife
<br />Refuge about 321 km upstream, However, those
<br />rearing ponds are well isolated from the river and
<br />escape or release is highly unlikely (risk analysis
<br />by the U.S, Fish and Wildlife Service estimated
<br />probability of hatchery escapement at only two
<br />fish every 100 years; B, Haines, pers, comm,),
<br />No intentional releases or unusual events likely
<br />to result in escapement were reported,
<br />Probable hatchling dates for our specimens, as
<br />revealed by daily-growth-ring analysis of their
<br />otoliths (lapillae), were 3 and 7 June, These dates
<br />correspond with the hatching dates for razorback
<br />suckers produced at the Ouray facility, but they
<br />are also consistent with the capture and obser-
<br />vation of ripe razorback suckers between 14 May
<br />and 10 June that year on a known spawning bar
<br />above Jensen, Utah, The probability that our
<br />captured juveniles represent natural production
<br />is also supported by more recent captures of pre-
<br />sumable razorback sucker larvae (mtDNA veri-
<br />fication pending) in both the middle and lower
<br />Green River, According to D, E, Snyder (pers,
<br />comm,) these larvae were taken by personnel of
<br />the U.S, Fish and Wildlife Service below the
<br />spawning bar near Jensen, in late May and early
<br />June 1992 and 1993 using drift nets, fine mesh
<br />seines, or light traps, They were also taken in
<br />light traps by the National Park Service and LFL
<br />at Old Charley Wash, just above Ouray, Millard
<br />Canyon and Anderson Bottom in Canyonlands
<br />National Park (about 34 and 38 km below Hell
<br />Roaring Canyon), and the lower end of Cataract
<br />Canyon in Lake Powell in early June 1993 (D,
<br />E, Snyder, pers, comm,),
<br />If recent captures of larvae are verified as ra-
<br />zorback sucker, successful spawning, production,
<br />and distribution of resultant larvae are more ex-
<br />tensive than expected, However, because larvae
<br />may drift great distances, we cannot yet assume
<br />that larvae or juveniles taken at downstream sites
<br />(e,g" lower Green River) originated there, That
<br />question can only be resolved by identifying spe-
<br />
<br />cific spawning grounds in those areas, Our cap-
<br />ture of two early juveniles suggests at least some
<br />low level of survival beyond the larval period,
<br />possibly through adult recruitment,
<br />Research emphasis should be placed on deter-
<br />mining the distribution and abundance of all life
<br />stages of razorback sucker in the lower Green
<br />River, and on factors (e,g" predation, habitat, and
<br />flows) that may limit recruitment.
<br />We thank D, Young who participated in the
<br />collection, D, E. Snyder and G, R, Smith for
<br />verification of razorback sucker specimens, and
<br />G, R, Smith for radiographing the fish, Review
<br />by D, E, Snyder and two anonymous reviewers
<br />enhanced the manuscript. Collection of these
<br />specimens was made possible through cooperative
<br />efforts of the Upper Basin Recovery Implemen-
<br />tation Program,
<br />
<br />LITERATURE CITED
<br />
<br />HOLDEN, p, B, 1980, Xyrauchen texanus (Abbott),
<br />Humpback sucker, Pp, 435, in Atlas of North
<br />American freshwater fishes (D, S, Lee et a!., eds,),
<br />North Carolina State Mus, Nat. Hist., Raleigh,
<br />LANIGAN, S, H" AND H, M, Tyus, 1989, Population
<br />size and status of the razorback sucker in the Green
<br />River, Utah and Colorado, N, Amer, J. Fish, Mgmt.,
<br />9:68-73,
<br />MARSH, p, C" AND W, L. MINCKLEY, 1989, Obser-
<br />vations on recruitment and ecology of razorback
<br />sucker: lower Colorado River, Arizona-California-
<br />Nevada, Great Basin Nat., 49:71-78,
<br />MCCARTHY, M, S" AND W, L. MINCKLEY, 1987,
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<br />ostomidae) from Lake Mohave, Arizona and Ne-
<br />vada, j, Arizona-Nevada Acad, Sci" 21:87-97,
<br />MINCKLEY, W, L. 1983, Status of the razorback suck-
<br />er, Xyrauchen texanus (Abbott), in the Lower Col-
<br />orado River Basin, Southwestern Nat., 28:165-187,
<br />MINCKLEY, E, L., p, C, MARSH, j, E, BROOKS, j, E,
<br />JOHNSON, AND B, L. JENSEN, 1991, Management
<br />toward recovery of the razorback sucker. Pp, 303-
<br />357, in Battle against extinction: native fish man-
<br />agement in the American west (W, L. Minckley
<br />and j, E, Deacon, eds,), Univ, Arizona Press, Tuc-
<br />son,
<br />SMITH, G, R, 1959, Annotated checklist of fishes of
<br />Glen Canyon, Pp, 195-199, in Ecological studies
<br />of the flora and fauna in Glen Canyon (A, M,
<br />Woodberry, ed,), Univ, Utah Anthro, Pap,
<br />SNYDER, D, E" AND R, T. MUTH, 1990, Description
<br />and identification of razorback, flannelmouth, white,
<br />Utah, bluehead, and mountain sucker larvae and
<br />early juveniles, Colorado Division of Wildlife, Den-
<br />ver, Colorado, Tech, Pub, No, 38,
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