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<br />ICHTHYOLOGICAL NOTES
<br />formerly might have included bonytail habitat.
<br />Water temperatures there are most affected by
<br />air temperature; discharge is the fifth most im-
<br />portant independent variable affecting water
<br />temperature (after air temperature, solar ra-
<br />diation, wind speed and cloud cover, respec-
<br />tively) (Bob Green, Regional Hydrologist, U.S.
<br />Fish and Wildlife Service, Denver, Colorado,
<br />pers. com.). Nonetheless, bonytail are very rare
<br />in these areas. The same holds true for the low-
<br />er Green, where temperatures are not affected
<br />by operation of Flaming Gorge Dam but where
<br />a viable bonytail population no longer occurs.
<br />Factors other than alteration of temperature
<br />regimes must have eliminated bonytail from
<br />these river reaches. This same conclusion was
<br />reached by Marsh (1985) for some reaches of
<br />the lower Colorado. Operation of upstream
<br />dams has reduced seasonal-high discharges and
<br />increased seasonal-low discharges in these
<br />reaches, but it seems unlikely that a species like
<br />bonytail-which evolved under the wide vari-
<br />ety of discharge conditions characteristic of the
<br />seasonally dynamic Golorado River system-
<br />would have been affected directly by such mod-
<br />eration of discharge regimes. These river
<br />reaches have been successfully colonized by sev-
<br />eral introduced species (Tyus et al., 1982); per-
<br />haps these species or synergic effects of these
<br />species and the altered discharge regimes have
<br />had important effects on bonytail.
<br />Acknowledgments.-We thank G. H. Clemmer,
<br />P. B. Holden, R. R. Miller, W. L. Hinckley and
<br />G. R. Smith for their opinions on the identity
<br />of the bonytail. We thank colleagues and an
<br />anonymous reviewer for criticisms that greatly
<br />improved this manuscript. These observations
<br />were made as part of an investigation funded
<br />by the U.S. Bureau of Reclamation and the Mu-
<br />nicipal Subdistrict, Northern Colorado Water
<br />Conservancy District.
<br />LITERATURE CITED
<br />BOZEK, M. A., L.J. PAULSON AND J. E. DEACON. 1984.
<br />Factors affecting reproductive success of bonytail
<br />chubs and razorback suckers in Lake Mohave. Lake
<br />Mead Limnological Res. Cent., Dept. Biol. Sci.,
<br />Univ. Nevada, Las Vegas. Tech. Kept. No. 12.
<br />GILBERT, G. H., AND N. B. SGOFIELD. 1898. NOteS On
<br />a collection of fishes from the Colorado basin in
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<br />HAMMAN, R. L. 1981. Hybridization of three species
<br />of chub in a hatchery. Prog. Fish-Cult. 43:140-141.
<br />1025
<br />. 1982. Induced spawning and culture of bon-
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<br />HOLDEN, P. B., AND C. B. STALNAKER. 1970. $y5[em-
<br />aticstudies of the cyprinid genus Gila, in the upper
<br />Colorado River basin. Copeia 1970:409-420.
<br />Huass, C. L. 1955. Hybridization between fish species
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<br />JORDAN, D. S. 1891. Report of exploration in Col-
<br />orado and Utah during the summer of 1889, with
<br />an account of the fishes found in each of the river
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<br />AND B. W. EVERMANN. 1896. The fishes'Df
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<br />Wiley and Sons, New York, New York.
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<br />MILLER, R. R. 1961. Man and the changing fish fauna
<br />of the American Southwest. Mich. Acad. Sci. Arts
<br />Lett. 46:365-404.
<br />HINCKLEY, W. L. 1973. Fishes of Arizona. Sims
<br />Printing Co., Inc., Phoenix, Arizona.
<br />1983. Status of the razorback sucker, Xy-
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<br />er basin. Southwest. Nat. 28:165-187.
<br />AND J. E. DEACON. 1968. Southwestern fishes
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<br />159:1424-1432.
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<br />Press, Inc„ Washington, D.C.
<br />SMITH, G. R., R. R. MILLER AND W. D. SABLE. 1979.
<br />Species relationships among fishes of the genus Gila
<br />in the upper Colorado River drainage. U.S. Natl.
<br />Park Serv. Trans. Proc. Series 5:613-623.
<br />TYUS, H. M., B. D. BURDICK, R. A, VALDEZ, C. M.
<br />HAYNES, T. A. LYTLE AND C. R. BERRY. 1982. Fish-
<br />es of the upper Golorado River Basin: distribution,
<br />abundance, and status, p. 12-70. In: Fishes of the
<br />upper Colorado River system: present and future.
<br />W. H. Miller, H. M. Tyus and C. A. Carlson (eds.).
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<br />VANICEK, C. D., AND R. H. KRAMER. 1969. Life h15-
<br />tory of the Colorado squawfish, Ptychocheilus Lucius,
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<br />River in Dinosaur National Monument, 1964--1966.
<br />Trans. Amer. Fish. Soc. 98:193-208.
<br />VANICEK, C. D., R. H. KRAMER AND D. R. FRANKLIN.
<br />1970. Distribution of Green River fishes in Utah
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<br />Dam. Southwest. Nat. 14:297-315.
<br />LYNN R. KAEDING, BOB D. BURDICK, PATRICIA
<br />A. SCHRADER AND WILLIAM R. NOONAN, U.S.
<br />Fish ¢nd Wildlife Service, Colorado River Fishery
<br />Project, 529 25%z Road, Grand Junction, Colo-
<br />rado 81505. Accepted 21 Nov. 1985.
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