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!~ <br />tit <br />8R CALIFORNIA FISH AND GAME <br />Missouri River (Berner 1951 ), 54% of materials ingested by' fishes was of terres- <br />trial origin. The sparse terrestrial vegetation of most of the Colorado River basin, <br />and relatively large size of the stream in proportion to its narrow, water-limited <br />riparian zone, diminishes the importance of allochthonous input. As emphasized <br />by Minshall (19781, autochthonous conditions are far more prevalent in open, <br />western streams than has been generally recognized. <br />Organic and inorganic transport in the Colorado River are curtailed by reser- <br />voirs, e;:cepting for downstream passage of plankton and associated suspended <br />debris through penstocks. These materials and nutrients not trapped by im- <br />poundments CPaulson and Baker 1980), nonetheless form a basis for down- <br />streamproduction. The few backwaters that remain along the river appear highly <br />productive, supporting large standing crops of planktcn, rooted aquatic vegeta- <br />tion, and fishes (Minckley 1979, Nicola 1979), all of ~tihich are flushed into the <br />channel by almost-tidal fluctuations in the stream resulting from hydroelectric <br />generation and pulses of irrigation deliveries. less modified readies of the river <br />-and those wliicli are relatively stabilized have proportionately more backwater <br />habitat. In-stream productivity is also locally high, enhanced by current under <br />abundant insolation without interference of shading by turbidity or riparian <br />vegetation, and is at present further augmented by addition of nutrients through <br />return flow of irrigation systems. A trophic economy based upon autochthonous <br />detritus establishes quickly under such conditions. <br />Introduced forage species that have survived and flourished in the lower <br />Colorado River mainstream all depend heavily upon detritus or primary produc- <br />ers, or upon secondary consumers such as zooplankton, chironomids, or other <br />invertebrates. Large fishes with less piscivorous tendencies feed directly upon <br />detritus- or plant-dependent clams or crayfish. The introduced fish fauna thus <br />appears to have relatively simple food interrelations. <br />ACKNOWLEDGMENTS <br />Research was supported in part by Contract 14-06-300-2529 from the U.S. <br />Department of Interior, Bureau of Reclamation, Lower Colorado River Division, <br />Boulder City, Nevada, which also gave permission for this publication. 1. 1• <br />Landye, J. Warnecke, and W. T. Kepner. plus numerous fisheries students at <br />Arizona State University helped collect and analyze the data; their assistance is <br />gratefully acknowledged. <br />REFERENCES <br />Bailey, R. M., and N. M. Harrison. Ir. 1948. Food habits of southern channel catfish Ucrahirus hcvstrir <br />puncfarusl in the Des Moines River, Iowa. Am. Fish. Soc., Trans., 80:119-139. <br />Berner, L. A. 1951. Limnology of the Tower Missouri River. Ecology 32:1-12. <br />Bradley, W. G., and (. E. Deacon. 1967. The biotic communities of southem Nevada. Pages 20I-295 in H, M <br />Wormington and D. Ellis, eds. Pleistocene studies in southem Nevada. Nev. State P.~us. Anthropol. Pap.. No. <br />13. <br />Brown, D. E., N. B. Carmony, and R. M. Turner. 1978. Drainage map of Arizona showing perennial stream and <br />some important wetlands. Ariz. Game and Fish Dept., Phoenix. <br />Brown, D. E., and C. H. Lowe. 1980. Biotic communities of the Southwest. U.S. Dept. Agric., For. Serv., Gen. <br />Tech. Rep., Rh1-78, map. <br />Calhoun, A. I. 1966. Inland fisheries management. Calif. Fish and Game Dr-pt., sacramento. <br />Cowell, B. C., and P. L. Hudson- 1967. Some environmental factors influencing benthic invertebrates in two <br />Missouri River reservoirs. Pages 54I-555 in C. E. Lance., eef., Reservar fishery symposium. Am. Fish. Soc. <br />spec. Publ. <br />Dill, W. A. 1944. The fishery of the lower Colorado River. Calif. Fish Carne, 30:109-211. <br />Edmondson, W. 7. <br />Edwards, G. L 19%~ <br />(Arizona-CaGfo <br />Fvermann, B.'N. 19: <br />Fish and Game <br />Har•ington, R' W., 1 <br />marsh: from or <br />Flynes, H. 8. N. 195C <br />a review of me <br />Jonez, .4., R. D. Be <br />Fisheries Task <br />(processed). <br />Kimsey, l B. 1958. <br />Soc., Trans., 9' <br />Miller. R. R. 1952. <br />a key for their <br />. 1961. <br />46:36504. <br />Miller, R. R., and C <br />Arizona. Univ <br />Minckley, W. L. l~ <br />.1971b. <br />Ariz. Stale l:r <br />_ .1973. F <br />. 1979. A~ <br />Contr. 14-06 <br />Minshall G. W. 1' <br />Moffett, J. 1V. 194 <br />Moyle, P. B. 19.'6 <br />Nicola. S.I. 1979. <br />Inland Fish_ E <br />R. R. lohnsor <br />a syrnpo5ium <br />Paulson, L. l ,anc <br />1656 in Sym <br />Portz, D. 1973. F <br />M. 5. Thesis <br />Prokocovich, N. <br />Ricker, ~4'. E. 193 <br />Lake, BritisF <br />P.inne. J. N., W'. <br />central Ariz: <br />schulback, I. C., . <br />Sci. 41:1nt- <br />Usin¢er, R. L. 1~ <br />Wallis, O. l- 1'2`- <br />Am. Fish. S <br />Nleaver, R O„ <br />Resen oir. . <br />\~'inn, H. E., anc <br />~denGficatic <br />