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INTRODUCTION General The Rifle to Debeque, Colorado, reach of the Upper Colorado River is historical habitat for both Colorado pi7ceminnow (Ptychocheidus Lucius) and razorback sucker (Xyrauchen texanus), and is designated critical habitat for both listed fishes (59 FR 13374-13400) under authority of the Endangered Species Act. Colorado pikeminnow are thought to have occupied the stream reach upstream from Government Highline Diversion Dam (i.e., Grand Valley Water Users) (Pressey 1968). Historical accounts and records of Colorado pikeminnow upstream of this diversion dam aze scant. The last and only record is from an anecdotal account of the capture, by angling, of a 381 mm (15-inch) Colorado pikeminnow, upstream from Glenwood Springs, Colorado (see Kesler 1998). In the eazly 1960s, fishermen reported catching Colorado pikeminnow in Plateau Creek (personal communication, George Kidd; Kidd 1974). Investigators conducting fishery surveys in warmwater reaches of Plateau Creek from the mouth upstream did not report collecting any razorback sucker or Colorado p~ceminnow (Carlson and Platania 1984; -Wick and Hawkins 1983). Plateau Creek is a small tnbutary to the Colorado River; the confluence being approximately 0.4 miles downstream from Government Highline Diversion Dam (river mile [RM] 193.7). The last two wild adult razorback sucker captures in a riverine environment upstream of Government Highline Diversion Dam were in 1981 at RM 220.7 and 223.5 neaz Pazachute, Colorado (Valdez et al. 1982). One adult razorback sucker was collected in 1991 from an isolated pond (RM 234.8) downstream from Rifle (Burdick 1992). Since 1991, over 100 sub-adult and adult razorback sucker were collected from Etter Pond (RM 204.5), a human-made gravel pit, immediately downstream from Debeque. The State of Colorado's former stocking plan (Kesler 2001) called for stocking both juvenile (150 mm) Colorado pikeminnow and sub-adult (Z 300 mm) razorback sucker in the Upper Colorado River from Rifle to Debeque Canyon. The plan prescn`bed stocking 1,340 Colorado pikeminnow per year for 9 years and 5,480 razorback sucker per yeaz for 8 yeazs, if available, starting in the fall of 2002. The stocking objective for this river reach was to achieve a minimum viable population of 575 adult Colorado pdceminnow from ages seven to nine. For razorback sucker, the stocking objective was to achieve a minimum viable population of 5,800 adult razorback sucker from ages five to seven distributed over 150 river miles among three river reaches in Colorado (Colorado River: Rifle to Debeque Canyon and Palisade, Colorado, to the Colorado/Utah stateline; Gunnison River: Hartland Dam [RM 60] immediately upstream from