!~
<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 />
|