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"[inCK1_11O. C. 1 ?t' ?'I b n.d. lictcs rower ri qht - t cprr c c. Stream use by Exotic and Native Fishes, Grand Canyon National Park, with 11 Observations on their Food Habits and Reproductive Cycles in 1976-1977. C. O. Minckley Biology Department Museum of Northern Arizona Flagstaff, Arizona 86001 Abstract--Investigations of the fishes of the Grand Canyon region have increased in recent years, however there is little information-per_ taining to the life histories of the fishes occurring in these studies. This presentation provides information collected during 1976-1977 on the food habits, reproductive cycles, and stream use of three common Grand Canyon _ashes, vise _a=r,",w _=ou- arc^k:2..e dace and b-'-..$.... mountain- sucker. Rainbow trout were found to eat several types of organisms, however their main food sources were mayflies, midges and black flies. They also occasionally ingested fish, i.e., speckled dace, larval bluehead mountain-suckers and trout eggs. Spawning in this exotic species began in late fall when water temperatures dropped below 100 C, and continued until early spring in all of-.the systems investigated. After that time, all of the streams were nursery areas, until the next spawning season. Rainbow trout were always present in Bright Angel Creek and used Phantom and Pipe Creeks sporadically. General distribution was that of smaller rainbows occurring in these streams during the late spring through early fall, while adult fish were present through late fall to early spring. The main food items of the speckled dace were mayflies, midges and black flies. Reproduction in this species occurred in April-May at water temperatures of 15-190 C, and was completed by June. Speckled dace were present in all of these streams also, but illustrated a dist- ribution essentially the reverse of the larger rainbow trout, being present during the late spring through the early fall, after which they were unobtainable by the collector. It is thought that this disappearance was due to the presence of spawning rainbow trout and was observed in all of the streams investigated. Bluehead mountain-suckers were found to utilize periphyton as their major food source, although midges, black flies and caddisflies did occur in diets. This species spawned in the various tributaries during April- May when water temperatures ranged from 15-190 C. Distribution of this fish was similar to speckled dace, with more bluehead mountain-suckers occurring in the stream systems investigated when larger rainbow trout were absent. f ( ?e : pp,-s . 41is? Gav4c? J Wi il ?K9 D