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o ~Four Comers Bridge (RM 119.2), and five above the Mixer in New Mexico (RM 136.6) (Ryden and ~Pfeifer 1995b). Six of these fish were monitored during the remainder of 1994, and the other fish C-)were monitored for shorter periods oftime. Similar to habitat use in the Green River System, the C radiotagged razorbacks used primarily slow water habitats in March and April, including eddies, pools, backwaters, and shoals that were typically warmer than the ma:inchannel habitats (Ryden and Pfeifer 1995b). During June and August, mainchannel fast water run habitats were used the most by the radiotagged razorbacks. This information indicated that subadult razorbacks stocked in the San Juan River selected habitats on a seasonal basis that were very similar to habitats selected by adults in the Green River (Tyus 1987). Ryden and Pfeifer (1995b) indicated that the slow water habitats used in the spring were relatively rare habitats in the river, whereas the runs used in the summer were fairly common habitats. On October 27, 1994, an additional 16 razorback sucker equipped with 2-year radiotags were stocked at the same sites as the spring stocking (Ryden and Pfeifer 1996b). These fish were of the same cohort as the fish stocked in March, but were larger, averaging 403 mm. In September 1995 an additional 16 razorback were radiotagged and stocked in the same locations in the San Juan River. Information on habitat use was obtained through 46 contacts with radiotagged fish during 1995. Unlike the spring 1994 samples, razorback sucker in spring 1995 primarily used mainstream run habitat rather than slow water habitats. These habitats were the same temperature as most of the remainder of the river. Runs continued to be the favored habitat throughout the remainder of 1995, with only June observations showing significant use of low velocity habitats. Reasons for the apparent change in preferred habitat between 1994 and 1995 are not known but may be related to differences in size of the fish and differences in flow during these 2 years. No youn'g wild razorbacks have been collected in the San Juan River during the 1987-1995 period oftms report, so habitat use by small razorbacks is not known. !tis likely that smaller razorbacks would also use habitat types similar to the ones that have been collected from in the Green River and other Upper Basin rivers. These habitats include backwaters and flooded bottomlands. Other Native Fishes Habitat requirements for other native fishes are poorly understood. Relatively little information is available from other portions of the Colorado Basin on habitat use of other native species. Three other native fish, flannelmouth sucker (flannelmouth), blue head sucker, and speckled dace, are relatively abundant in the San Juan River study area (Platania 1990; Propst and Hobbes 1993; 1994, 1995; Ryden and Pfeifer 1993, 1994, 1995a). Although habitat requirements for these species have not been specifically studied, the study area appears to meet the requirements of these species since they are found in large numbers. . ~, Roundtail chub (roundtail) are also typically found in relatively high numbers in some Upper Colorado River Basin streams, but they are very rare in the San Juan River. Although also not well documented, roundtail chub are typically found in pools and eddies in tributaries and the upper portions of main stem rivers in the Upper Colorado River Basin (Holden and Stalnaker 1975). Ryden and Pfeifer (1993, 1994, 1995a, 1996a) studied adult fish in the system and caught only 2 in 1991, 4 in 1992,2 in 1993,4 in 1994, and 4 in 1995, fewer numbers than Colorado squawfish for the same time period. San Juan River Recovery Implementation Program Summary Report 26 17 January 1997 PR-576-2