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T -j yJS ,Qr5 b ~o~ / or"'; (/<) / ;"<yvyJ 073JL 184 Status of the Razorback sucker in the Green River, Utah Harold M. Tyus U. S. Fish and Wildlife Serivce-CRFP 1680 W. Hwy. 40 Room 1210 Vernal, UT 84078 Abstract--The razorback sucker, once widely distributed in the mainstem rivers of the Colorado River Basin is still found today in riverine habitat of the Green River Basin, where it may be more numerous than in other locations in the Upper Colorado Basin. Although historic data prior to 1970 is scant, records from the 1890.s suggest that the fish was never as abundant in the upper basin as in the lower. Some areas formerly supporting the razorback in the upper basin have been altered by water development and the fish extirpated from them. The Fish and Wildlife Service has studied the rare and endangered fishes in the Green since 1979. A systematic sampling program from 1979-81 indicated that the razorback was very rare, and was only 11% as abundant as the endangered Colorado squawfish. However, subsequent studies from 1981- 84, including radiotelemetry, revealed that the razorback is not very susceptible to capture except during spring spawning. Razorback spawning was documented from 1981-84 with the capture of 47 fish in breeding condition and tentative identification of larvae. Since no young juveniles were collected, recruitment is apparently very low. Growth of adults measured from the interval between capture/recapture of tagged fish (from 16 years) averaged less than 5 mm/year. These data suggest that the razorback should be considered endangered in the upper basin and immediate steps should be taken to protect and recover it. 1 r. I 'I " (II I ~ gS- 0e~M' tlsJ.-.>.( C""Y'-C' "" )