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<br />Hamilton
<br />
<br />trations found in water and biota in the NIWQP studies and by others, but
<br />which are lower than these reported in the 1930s.
<br />In retrospect, the extremely elevated selenium concentrations in the Colo-
<br />rado, Gunnison, Uncompahgre, and Sanjuan rivers and their uibutaries from
<br />the mid-1930s, which presumably started in the 1890s when irrigation activities
<br />began, would be expected to have had a devastating effect on native fish, based
<br />on adverse effects demonstrated in recent studies with endangered fish and
<br />numerous other species. This adverse effect was recognized indirectly as the
<br />disappearance around the 1910 to 1920 period of large-river fish such as
<br />Colorado pikeminnow. and razorback sucker before large dams were con-
<br />structed in the upper Colorado River basin. In the lower basin these fish were
<br />found until 1911 in abundance in irrigation ditches, but by 1925 to 1930 were
<br />considered scarce. The statement of Minckley et at. (1991) about the suiking
<br />historical absence of young razorback sucker in collections suggests reproduc-
<br />tive failure probably was occurring, i.e., no recruitment of young fish to the
<br />population, which is one of the well documented effects of selenium exposure.
<br />There is little doubt that the construction of mains tern reservoirs and
<br />introduction of exotic species have conuibuted to the decline of endangered
<br />fish in the Colorado River. There is now evidence that selenium, historically
<br />and currently, may be conuibuting to the endangerment of fish in the Colo-
<br />rado River basin.
<br />
<br />ACKNOWLEDGMENTS
<br />
<br />I thank R. Engberg and T. Presser for reviewing this paper, and Karen
<br />Faerber for typing the manuscript.
<br />
<br />REFERENCES
<br />
<br />Anderson, M. S., Lakin, H. W., Beeson, K. C., Smith, F. F., and Thacker, E. 1961.
<br />Selenium in agriculture. U.S. Deparunent of Agriculture, Washington, DC. Agricul-
<br />ture Handbook No. 200.
<br />Andrews, B.]., King, K. A., and Baker, D. L. 1997. Environmental contaminants in fish
<br />and wildlife of Havasu National Wildlife Refuge, Arizona. U.S. Fish and Wildlife
<br />SelVice, Phoenix, AZ.
<br />Barnhart, R. A. 1957. Chemical factors affecting the sulVival of game fish in a western
<br />Colorado reservoir. Master's thesis, Colorado State University, Fort Collins.
<br />Beath, O. A. 1943. Toxic vegetation growing on the salt wash sandstone member of the
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<br />Beleau, M. H., and Bartosz, J. A. 1982. Acute toxicity of selected chemicals: data base.
<br />In: Colmado River Fishery Project Final Report Contracted Studies, Report No.6, pp. 242-
<br />254. U.S. Fish and Wildlife Service, Salt Lake City, UT.
<br />Bell-McCaulou, T. M. 1993. Corbicula fluminea as a bioindicator on the lower Colorado
<br />River. Master's thesis. University of Arizona, Tucson.
<br />Bestgen, K. R. 1990. StatuS review of the razorback sucker, Xyrauchen texanus. U.S.
<br />Bureau of Reclamation. Colorado State University, Fort Collins, CO. Report.
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