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1 t INTRODUCTION The razorback sucker (Xyrauchen texanus) is an endangered fish native to the Colorado River drainage of the Southwestern United States. Records of its capture in Canyonlands National Park have been extremely rare, undoubtedly due to the difficulty of sampling these remote reaches and possibly due to the rarity of the species. To our knowledge, no wild razorbacks have been captured in the past decade (Tom Chart, UDNR, personal communique) and only a few fish were taken prior to that period. Hinckley et al. (1991) ~; reported uncovering reports of only five razorback suckers being taken from Cataract Canyon and all were adults (Persons et al. 1982, Valdez et al. 1982, Valdez 1988). Holden conducted fish surveys within Canyonlands National Park between 1967- 1972 and reported razorback suckers were rare and juveniles absent (Holden 1973). Eight juveniles were reported captured between Moab and Dead Horse Point prior to Holden's effort in 1962-64 (Taba et al. 1965). By all accounts, it appears adults and especially juvenile razorback suckers have become extremely rare in the park during the past 4 decades. F ew extant populations of razorback sucker remain. Those remaining aze scattered, comprised by very few fish (Tyus and Karp 1990) which experience low or no recruitment (Hinckley 1983). The largest population occurs in Lake Mojave, '~ Arizona/Nevada, with a small population in Lake Mead's Las Vegas Cove, and occasional collections downstream from Lake Mojave in the Lower Colorado River and its associated canal system (Hinckley 1983, Marsh and Hinckley 1989). The largest remaining population of riverine razorback sucker occurs on the Green River between the Yampa and Duchesne Rivers of Northeastern Utah (Tyus 1987, Tyus and Karp 1990). Very few naturally-spawned juvenile razorback suckers have been collected in the Colorado River drainage in recent history (but see Gutermuth et al. 1994, Marsh and ~; Hinckley 1989, Modde 1996, Modde et al. 1996), despite adult suckers being collected, albeit very rarely. Recently fisheries biologists in Utah, Colorado, Nevada, New Mexico, and Arizona have begun razorback sucker stocking programs to compensate for the razorback sucker's low rate of recruitment (Burdick and Bonar 1997, Langhorst 1989, Pfeifer and Burdick 1998, Ryden and Pfeifer 1995). Historical efforts to enhance the dwindling populations of razorback suckers in the lower Colorado River (Langhorst 1989, Marsh and Hinckley 1989) by stocking hatchery-reared larvae and small fish appeared to have failed (Hinckley et al. 1991). In 1986, more than 1.4 million larvae were stocked into the Colorado River from Topock Gorge (just downstream from Davis Dam) to neaz Yuma. The U.S. Fish and Wildlife Service (USFWS) was able to capture only 41 juvenile razorback suckers from the original 1.4 million larvae (Mazsh and Hinckley 1989). Although the return seemed small, Hinckley (1995) pointed out that between 1981 and 1989 ~15 million razorback sucker larvae were stocked in the lower Colorado River, and if only 0.1 % survived, then we should have ~, only expected to encounter slightly less than one fish per surface hectare of water. 1 t