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1995]
<br />DIETS OF FISHES IN BACKWATERS
<br />103
<br />fish species collected during summer and autumn 1987 from backwaters in two reaches of the Green River below its
<br />with mean of volume percentages as the diet measure; values >0.60 (biologically important overlap) are marked with an
<br />
<br />
<br />
<br />
<br />Fathead Flannelmouth
<br />minnow Speckled dace Bluehead sucker sucker Channel catfish Green sunfish
<br />Lower Upper Lower Upper Upper Lower Upper Lower Upper Lower
<br />11-2021-30 31-40 >40 21-30 21-30 31-40 21-30 31-40 >40 31-40 >40 >40 >40 21-30 31-40 >40 >40 21-30 >40
<br />0.44 0.43 0.37 0.33 0.21 0.36 0.34 0.39 0.35 0.34 0.52 0.57 0.59 0.34 0.46 0.34 0.30 0.21 0.56 0.25
<br />0.22 0.21 0.15 0.11 0.37 0.59 0.57 0.16 0.12 0.11 0.46 0.45 0.65* 0.83* 0.72* 0.61* 0.57 0.73* 0.91* 0.26
<br />0.21 0.21 0.15 0.12 0.52 0.76* 0.61* 0.20 0.16 0.19 0.42 0.36 0.69* 0.89* 0.81* 0.75* 0.75* 0.73* 0.75* 0.27
<br />0.21 0.21 0.14 0.10 0.42 0.78* 0.61* 0.14 0.11 0.11 0.38 0.31 0.69* 0.68* 0.81* 0.79* 0.82* 0.61* 0.69* 0.27
<br />0.21 0.20 0.14 0.10 0.35 0.74* 0.58 0.14 0.10 0.10 0.38 0.31 0.63* 0.64* 0.69* 0.89* 0.77* 0.68* 0.57 0.24
<br />and might have a negative impact on Colorado
<br />squawfish growth, condition, or survival.
<br />Studies are needed to better assess the type
<br />and strength of interactions between native
<br />and nonnative fishes in backwater food webs
<br />under present regulated flow regimes and to
<br />define factors affecting these interactions.
<br />ACKNOWLEDGMENTS
<br />H. Tyus, C. Karp, and S. Lanigan initiated
<br />this study and provided samples and field
<br />data. H. Copeland, J. Piccolo, and P. Sikoski
<br />assisted with analysis of gut contents. H. Tyus
<br />and C. Karp reviewed data analyses. K.
<br />Bestgen, D. Beyers, J. Deacon, G. Haines, J.
<br />Hawkins, C. Karp, H. Tyus, and R. Valdez
<br />reviewed drafts of the manuscript. This proj-
<br />ect was funded by the Recovery Implemen-
<br />tation Program for Endangered Fish Species
<br />in the Upper Colorado River Basin. The pro-
<br />gram is a joint effort of the U.S. Fish and
<br />Wildlife Service, U.S. Bureau of Reclamation,
<br />Western Area Power Administration, states of
<br />Colorado, Utah, and Wyoming, upper basin
<br />water users, and environmental organizations.
<br />This paper is Contribution No. 75 of the Colo-
<br />rado State University Larval Fish Laboratory.
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<br />biology. Volume 1. Iowa State University Press,
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<br />1977. Handbook of freshwater fishery biology.
<br />Volume 2. Iowa State University Press, Ames. 431
<br />PP.
<br />CARLSON, C. A., AND B. T. MUTH. 1989. The Colorado
<br />River: lifeline of the American Southwest. Pages
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<br />between young of the year of two sympatric tui chub
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<br />spawner. Transactions of the American Fisheries
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<br />of trophic interactions in selected backwaters and
<br />the main channel of the Green River, Utah. Final
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<br />Laboratory Services Division, Applied Sciences
<br />Branch, Environmental Sciences Section, Denver, CO,
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<br />Regional Office, Salt Lake City, UT. 131 pp.
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<br />among fishes of the Virgin River. Copeia 1988:
<br />314-323.
<br />HAINEs, G. B., AND H. M. TYus. 1990. Fish associations and
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<br />Ecology 5: 427-435.
<br />HARLAN, J. R., E. B. SPEAKER, AND J. MAYHEW. 1987. Iowa
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<br />HURLBERT, S. H. 1978. The measurement of niche overlap
<br />and some relatives. Ecology 59: 67-77.
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