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30 'Table 4. Endangered or Threatened Wildlife AQuatic Ecosystems. Biological subbasins are based primarily on fish distributions which are, in turn, a function of physical character- *Mexican duck Anas diazi istics which affect fish life. To a great extent, stream elevations Falcon mexicanus describe the distributions of fish because of the relationship between elevation and temperature. Although fish species operate within given *Yuma clapper rail Rallus longirestris yumanensis *prairie falcon *American peregrine Falco peregrinus anatum temperature ranges, in some cases quite wide, temperature is a major Euderma maculatum variable controlling species distribution. Spotted bat *Utah prairie dog Eynomvs parvidens Factors other than temperature nave a significant effect on ecotype. Sciuvus kaibabenus Silt loads, stream gradient, and food chains also have major impacts on Kaibab squirrel Sonoran pronghorn Antilocapra americana sonoviensis fish communities and these are reflected in the ecotype classification Arizona prairie dog Cynomys ludovisianus arizonensis (for streams only, figure 2). If significant inputs of natural or man- Chiricahua squirrel Sciurus chiricahuae induced concentrations of materials occur which directly affect adult .. .. .. .. .. Apache fox squirrel Sciurus apache fish, their life cycles, their food chains, or their habits, then the < fish will not be found in that particular ecotype. Thus, the distribu- tions shown in figure 2 would be characteristic of the stream community ~ I( .. .. * On the endangered species list; others noted are being considered. The list of considered animals is much greater than is presented in the table but these are assumed most likely to be added. for "natural conditions" assuming no waste loadings of deleterious mate- Much of the higher elevation streams are considered trout habitat. ~ ~ .. ~ ~ .. .. .. rials by human activities, exclusive of thermal discharges. This results largely from temperature-related phenomena, but also re- fleets the clear water, good food chain development, and unusually high gradient streams. In the next lower reaches of the river system there is a transition between trout waters and mainstream stretches. Whitefish characterize this type of water in the upper basin. Whitefish require high quality water and have relatively strict habitat requirements which make them a good index of the effects of human activities on the river ecosystem. However, they may be eliminated by flow decreases,