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f"'- r.- r'- 'f-4 C) <..~ .- :~ .:~ :. ~. .'-.:.; Studies by Ryden and Pfeifer (1993, 1994, 1995a, 1996a) used radio telemetry and standard sampling methods (electro fishing and netting) to look at adult Colorado squawfish habitat in the San Juan River. Based on 83 ground contacts made using radio telemetry, of adult Colorado squawfish over a 5-year period, 52 percent of the contacts were from run habitats, 18 percent were from eddy habitats, and 12 percent were from shoreline habitats. This differed from the habitats used in the Green and Yampa rivers where shorelines were used more than 50 percent of the time. In addition, Ryden and Pfeifer (1993, 1994, 1995a, 1996a) also noted that movement of San Juan River squawfish was less than that observed in the Green River System. Movement in the San Juan River generally occurred within a 30 mile corridor between RM 119 and RM 148. Home ranges of San Juan squawfish also were smaller and the fish were more sedentary than most other populations, except in 1995 when mean total longitudinal movement more than doubled compared to the previous 4 years (40 miles versus 10 to 20 miles). The reasons for the rather dramatic changes in longitudinal movement in 1995 are not known but may be related to the small number of radio contacts (four) that occurred in 1995 (Ryden and Pfeifer 1996a). The shortened movement and home range seen during these studies is more similar to squawfish in the "15-mile reach" of the Colorado River near Grand Junction than any other known population. Colorado squawfish in the San Juan River also used only one tributary, the Mancos River (RM 122.6), and then only the mouth of that river during runoffperiods. The mouth of the Mancos River is dammed by the flow of the San Juan River at this time and provides a "backwater" type habitat. Ryden and Pfeifer (1993,1994, 1995a) also noted that adult squawfish used a portion of the San Juan River known as" the Mixer" (RM 129.8 to RM 133.4) during the purported spawning period. Many of the fish tracked to the Mixer also used the mouth of the Mancos River as a prespawning staging area. Ripe fish were found together in the Mixer on probable spawning bars in 1992. Additionally, one fish in 1994 migrated to the Mixer from the Bluff, UT,an area about 58 miles upstream of the Mixer, remained there for about 2 months during the spawning period, and then migrated back to the Bluff area. This is very similar to migration behavior and habitat use that has, been documented in the Green River System. Findings in 1995 differed from those of.the previous years (Ryden and, Pfeifer 1996a). For one, no new Colorado squawfish were implanted with radiotags due to very low capture success of adult squawfish. Only seven contacts (radio contacts and netting and electro fishing captures or sightings) were made with Colorado squawfish in 1995. Only one of these was within the Mixer area; most of the others occurred in downstream locations. It is likely that the small number of contacts with Colorado squawfish caused the apparent change in which portions of the river they appeared to use in 1995. Miller (1994a) intensively followed four squawfish radiotagged by Ryden and Pfeifer (1994) from June 21 to August 13, 1993, between RM 122.6 and RM 142.0. During late June and early July the fish staged in eddies and secondary channels that were warmer than the main river, including the mouth of the Mancos River. By mid-July all four fish moved to two spawning sites at RM 131.15 and RM 132.0 within the Mixer. Both sites provided a variety of habitats, including fast, cobbled areas similar to those used for squawfish spawning in other rivers. Spawning behavior was observed during mid to late July, and the fish dispersed in late July. San Juan River Recovery Implementation Program Summary Report 23 17 January 1997 PR-576-2