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Razorback sucker In 1996, an "in-ladder" experiment was conducted with pond-reared razorback sucker. An aluminum punch-hole screen was placed at the downstream end of the fishway to prevent the razorback suckers from accidently escaping into the river. Two of these six razorbacks successfully ascended the fishway and were collected in the fish trap. However, to date (through July 2001) with some 43,910 razorback suckers that have been stocked in the Gunnison and Upper Colorado rivers, no other razorback sucker have been found in the fish trap. Seasonal and Annual Use/Movement Native Fish. Native fish used the passageway more often in June and July which corresponded with the runoff and subsequent post-runoff period in the Gunnison River. Native fish use tended to be highest in June in 1997, 1998, and 1999, although the overall 5-year total number (9,320) indicated that July was the highest month of use (Table 2). This was attributed to the high number (4,915) of native fish that used the passageway in July 1996, the first year of operation. Flannelmouth sucker used the passageway the most during July (3,468) and May (3,095) over the five years between 1996 and 2000 followed by June (2,710), and April (1,862) (Appendix; Table G.1. and Figure G.1.). The greatest number of bluehead sucker used the passageway in July (5,008) and June (4,652) during the same period followed by May (4,377), April (3,303), and August (2,301) (Appendix; Table G.2. and Figure G.1.). Roundtail chub used the passageway the most during June (1,100), followed by July (805), May (526), and August (447)(Appendix; Table G.3. and Figure G.1.). Annual usage was highest in 1997 for flannelmouth sucker (5,260), bluehead sucker (5,029), and roundtail chub (1,235)(Appendix; Figure H.1.). Usage was lowest in 2000 for flannelmouth sucker (1,212) and roundtail chub (412) whereas 1996 was the lowest usage year for bluehead sucker (3,786). Nonnative Fish. Twelve nonnative fishes and two nonnative sucker hybrids accounted for approximately 6.5% of the other fishes that used the passageway over the five years. This compared to nine different fish species and two hybrid sucker species that were collected during 1992 and 1993 in the Lower Gunnison River between the dam and confluence with the Colorado River (Burdick 1995). Nonnative species accounted for 23% of the total number of fishes collected in this river reach during those two years. Identical species composition and similar percentage composition (21X) were reported for this reach between March 1994 and November 1995 (Burdick 1997). 26