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Study 2: Winter habitat and flows for adult and young Colorado squawfish, and adult razorback sucker. Report 3- Winter habitat study of endangered fish-Green River. Wintertime movement and habitat of adult Colorado squawfish and razorback suckers. (Valdez and Masslich 1989) Ten radiotagged Colorado squawfish and eight razorback suckers overwintered in specific areas of the Green River during the winters of 1986- 87 and 1987-88. These areas were generally less than about 5 km, but maximum movement of Colorado squawfish ranged from 41.4 km downstream to 35.5 km upstream, and maximum movement of razorback sucker ranged from 16.8 km downstream to 11.7 km upstream. Colorado squawfish and razorback suckers exhibited local diel movements in selected low velocity microhabitats. These habitats were characterized by average water depth of 0.76 to 1.37 m and mean water column velocity of 0 to 0.31 mps for Colorado squawfish, and 0.61 to 1.37 m and 0.03 to 0.335 mps for razorback sucker. Movements of Colorado squawfish in eddies and backwaters (48.20 m/h) was greater than in slow runs and slackwaters (21.71 m/h), suggesting foraging in the former and resting in the latter. Greater local movement was exhibited by adult Colorado squawfish and razorback suckers exposed to fluctuating river levels, and flow fluctuation rates greater than 5 cm/h caused about 190 percent greater movement in adult Colorado squawfish and 39 percent greater movement in adult razorback suckers. This movement increased during periodic ice breakups. Fish in the upper 88 km of their distribution in the Green River can be expected to move more frequently than fish further downstream in order to remain in suitable microhabitats. The effect of this energy expenditure on survival, growth, and reproductive potential is unknown. (Authors abstract from Summary of Findings) Report 4- Winter habitat use of young Colorado squawfish. (Tyus, in litt.) Shoreline habitats and general river conditions were studied during the winters of 1987-88 and 1988-89. Weather conditions differed between the two winters, but ice cover generally formed by mid-December. Few fish were captured using baited minnow traps, but 5 young Colorado squawfish were collected in one backwater in December 1987 and one hatchery-reared juvenile razorback sucker was captured in 1988. Fluctuating flows in 1987-88 caused shoreline scouring in the Jensen area by moving blocks of ice, and alternate flooding and dewatering of low-lying areas at Ouray due to ice jams. Lower, more stable flows in 1988-89 resulted in shallower backwaters but less shoreline scouring. (Unpublished manuscript) Study 3: Spring-early summer flow requirements of Colorado squawfish, razorback sucker, and humpback chub.