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<br />116
<br />
<br />less than 2 m and water velocities averaged 0.5
<br />m/s.
<br />The razorback sucker is so rare that basic life
<br />history information is difficult to obtain for it, and
<br />its specific habitat requirements remain largely
<br />unknown. The apparent lack of recruitment and
<br />continuing water resource development dictates
<br />that immediate measures be taken to ensure sur-
<br />vival of the species before it is extirpated. The
<br />razorback sucker population in the Green River
<br />basin will likely continue to decline as old indi-
<br />viduals die without replacement. Few razorback
<br />suckers are reported from the remainder of the
<br />upper Colorado River basin (Tyus et al. 1982),
<br />and the Green River stock may be the largest one
<br />surviving in its native riverine environment. If
<br />further work does not soon identify the causes for
<br />decline, this interesting genus may disappear in
<br />nature.
<br />
<br />Acknowledgments
<br />These studies were funded in part by the U.S.
<br />Bureau of Reclamation, the U.S. Fish and Wildlife
<br />Service, and the U.S. National Park Service. B.
<br />D. Burdick, W. B. Harned, J. J. Krakker, R. M.
<br />McNatt, and L. A. Trinca were principals among
<br />the many U.S. Fish and Wildlife Service employ-
<br />ees who aided in gathering the data. K. M. Paulin
<br />aided in data retrieval. The states of Colorado and
<br />Utah provided logistical support. I thank J. E.
<br />Brooks, P. H. Eschmeyer, C. W. McAda, W. L.
<br />Minckley, and two anonymous referees for their
<br />reviews of the draft manuscript.
<br />
<br />References
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<br />mont North Carolina. Transactions of the Ameri-
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<br />Marsh, P. C. 1985. Effect of incubation temperature
<br />on survival of embryos of native Colorado River
<br />fishes. Southwestern Naturalist 30: 129-140.
<br />McAda, C. W., and R. S. Wydoski. 1980. The razor-
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<br />TYVS
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<br />Winter, J. D. 1983. Underwater biotelemetry. Pages
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<br />
<br />Received September 19, I98(i
<br />Accepted February 2, 1987
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