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BIOLOGY OF HUMPBACK CHUBS IN THE GRAND CANYON
<br />the past (Fig. 2), humpback chubs in the Col-
<br />orado can undergo normal seasonal gonad de-
<br />velopment up to the point of spawning. How-
<br />ever, we believe that significant reproductive
<br />success can occur only if mature fish enter the
<br />Little Colorado to spawn. Selection for devel-
<br />opment of such a spawning migration would be
<br />very strong, and our data suggest that some
<br />humpback chubs do move from the Colorado
<br />into the Little Colorado to spawn. The altera-
<br />tion of the Colorado River environment could
<br />have forced bonytails there to spawn in the low-
<br />er Little Colorado; some interbreeding might
<br />then have occurred with humpback chubs be-
<br />fore the bonytail stock was eliminated. Such hy-
<br />bridization between cyprinid species has been
<br />documented in other waters where environ-
<br />mental disturbance and the loss of reproductive
<br />habitat have occurred (see Gilbert 1961). There
<br />are evidently no chromosomal differences be-
<br />tween the two species that would prevent gene
<br />exchange between humpback chub and bony-
<br />tail populations, because fertile hybrids have
<br />been artificially produced in the hatchery. The
<br />humpback chub X bonytail hybrids produced
<br />by Hamman (1981) matured in the hatchery at
<br />2 years of age and were introgressively crossed
<br />with parent stocks; hatching success, about 60%
<br />at 17 C, did not differ among the F2 generations
<br />(Theophilus Inslee, Dexter National Fish
<br />Hatchery, USFWS, Dexter, New Mexico, per-
<br />sonal communication).
<br />Although the Little Colorado seems isolated
<br />from potential human-caused perturbations,
<br />perpetuation of this area as reproductive hab-
<br />itat for the humpback chub is not assured. Few
<br />species now live in the river, and competitive
<br />or predatory interactions may not have impor-
<br />tant effects on humpback chubs. The unsuita-
<br />bility of the Little Colorado and Colorado river
<br />environments for many of the fish species in the
<br />drainage could, in part, account for the persis-
<br />tence of humpback chubs in the Little Colo-
<br />rado. However, our collection of the redside
<br />shiner, a recent immigrant to the Colorado of
<br />the Grand Canyon, suggests that colonization
<br />of our study area by species for which this en-
<br />vironment is favorable might not be complete.
<br />Introduction to the Little Colorado of such a
<br />species that might prosper under the physico-
<br />chemical conditions of the river could have a
<br />devastating effect on the humpback chub in the
<br />Grand Canyon.
<br />593
<br />Acknowledgments
<br />We thank the many individuals who helped
<br />with the study, particularly Flagstaff field sta-
<br />tion personnel including C. O. Minckley, Kim
<br />Sylvester, Mike Hurley, Wendy Ripp, Don King,
<br />and Alan Fredericksen, and the many persons
<br />who provided a ready source of field assistance,
<br />Project Leader Bill Miller and Assistant Project
<br />Leaders Don Archer and Joe Valentine provid-
<br />ed valuable administrative and technical sup-
<br />port. Glenn Clemmer and Darrel Snyder veri-
<br />fied and provided identifications of fish species.
<br />Jerry and Donna Jacobi analyzed stomach con-
<br />tents of humpback chubs. Pathologic analyses
<br />were made by Rex Flagg. Charlie Smith per-
<br />formed the histologic work on humpback chub
<br />gonads. R. V. Bulkley, J. E. Johnson, and R.
<br />Pimentel commented on the manuscript.
<br />Dean Blinn and H. E. Graham, Biology De-
<br />partment, Northern Arizona University, pro-
<br />vided laboratory equipment and space. Norm
<br />Sharber designed and built the electrofishing
<br />boat and provided logistic support, as did Steve
<br />Carothers. Jim Walters, Grand Canyon Nation-
<br />al Park, as well as numerous other park per-
<br />sonnel, provided assistance throughout the
<br />study. Mary P. Young prepared the illustra-
<br />tions.
<br />Funding was provided largely by the United
<br />States Bureau of Reclamation; additional funds
<br />were provided by the National Park Service and
<br />the United States Fish and Wildlife Service. The
<br />Navajo and Hopi Indian Relocation Commis-
<br />sion provided office equipment and space.
<br />References
<br />BAUER, O. N. 1959. Parasites of freshwater fish and
<br />the biological basis for their control. Bulletin of
<br />the State Scientific Research Institute of Lake
<br />and River Fisheries 49, Leningrad, Russia.
<br />Translated from the Russian: National Technical
<br />Information Service, OTS 61-31056, Spring-
<br />field, Virginia, USA.
<br />BLAXTER, J. H. S. 1969. Development: eggs and lar-
<br />vae. Pages 177-252 in W. S. Hoar and D.J. Ran-
<br />dall, editors. Fish physiology, volume 3. Academ-
<br />ic Press, New York, New York, USA.
<br />COLE, G. A., AND D. M. KUBLY. 1976. Limnologic
<br />studies on the Golorado River from Lees Ferry
<br />to Diamond Creek. Colorado River Research
<br />Program, Grand Canyon National Park, Tech-
<br />nical Report 8, Grand Canyon, Arizona, USA.
<br />COOLF.Y, M. E., J. W. HARSHBARGER, J. P. AKERS, AND
<br />W. F. HARUT. 1969. Regional hydrology of the
<br />
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