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FISHES OF THE COLORADO RIVER IN GRAND CANYON NATIONAL PARKl Royal D. Suttkus2 and Glenn H. Clemmer3 The general decline in native fish populations in the American southwest has been documented in numerous studies (Dill 1944; Miller 1946 a,b; Wallis 1951; Minckley and Deacon 1968; Minckley 1973 and others). Isolated spring populations and residents of smaller tributaries have been particularly vulnerable to habitat losses and competition with introduced exotic forms. Species inhabiting large rivers have been similarly af- fected; however, their status is more difficult to ascertain. Almost 300 miles of the Colorado River through the Grand Canyon has been virtually inaccessible for ichthyological studies until re- cently. Float trips on large pontoon rafts have opened up the Canyon and have become increasingly popular in the past few years. This increased visitor pressure on the Colorado River and con- comitant attention toward vanishing wildlife re- sources has stimulated our studies on the status of the fishes of the Colorado River in the Grand Canyon National Park. Our study area extended from Lee's Ferry (which is 15 miles below Glen Canyon Dam) to the upper reaches of the Mead Reservoir at Pierce Landing (River Mile 280). Most of our 13 float trips were made in summer months; however, one trip was scheduled in mid-April and one was in late Sep- tember. Most of our collecting efforts were in the mouths and lower reaches of the various tribu- taries. The flow of the Colorado River through the Grand Canyon has been severely modified by the closure of Glen Canyon Dam in 1963. The seasonal floods and fluctuations of the river are now re- placed with variations in water levels which correspond to the generation of electricity. The natural temperature regime has also been modified as the water is discharged from the lower portion of the dam. During our study the water tempera- ture of the Colorado River was consistently 100C or colder in the upper portion of the river and gradually warmed to a high of 160C 250 miles down- stream. Tributary temperatures varied with the seasons. The still waters behind Glen Canyon Dam act as a silt trap for the normally turbid river, thus the present discharge from the dam is ex- tremely clear. Fish collections were obtained from thirty- five different sites along 280 miles of the Colo- rado River in Coconino and Mohave counties in Ari- zona. A total of 112 collections was obtained between September 1970 and June 1976. Nineteen species of fishes were represented of which fif- teen (79%) were introduced (exotics). The four native fishes were the humpback chub, Gila cypha, speckled dace, Rhinichthys osculus, flannelmouth sucker, Catostomus latipinnis, and blue head suck- er, Pantosteus discobolus. In addition to the nineteen species two different hybrid combina- tions were taken: the sucker hybrid Catostomus latipinnis x Xyrauchen texanus and various crosses IGrand Canyon National Park, Colorado River Research Series: Contribution No. 24; and Tulane University, Museum of Natural History: Contribution No. 10. 2Tulane University, New Orleans, Louisiana. 3M ississippi State University, State College, Mississippi. 599 of the rainbow trout, Salmo gairdneri with other species of trout. We presume the hybrid trout were artificially produced at some hatchery and then stocked in the canyon area. In comparison to many Eastern rivers (50 to 150 species) the Colorado River could not be con- sidered as species rich even before impoundment. Perhaps eight or as many as ten species once lived in the Grand Canyon area of the Colorado River. However few, most of the forms are unique and most occur nowhere naturally outside of the Colorado basin. Three of the four native fishes found in the area seem to be maintaining adequate populations. Perhaps their success is due to their ability to utilize a number of small tributaries as well as the larger tributaries for spawning. These three species are the speckled dace, Rhinichthys oscu- ius, flannelmouth sucker, Catostomus latipinnis, and the bluehead sucker, Pantosteus discobolus. The flannelmouth sucker, Catostomus latipin- nis (Figure 1, upper), is widespread in the Colo- rado River system and it was collected from sites throughout the Grand Canyon area, i.e., from Lee's Ferry downstream to the upper end of the Mead Reservoir. Adult, young or both were taken from fourteen tributaries and from nine sites along the main channel of the Colorado River. The main channel of the Colorado River prob- ably provided more spawning area prior to im- poundment than it does now. Although we assume that some spawning takes place in the main stream we did not record direct evidence. All spawning activities that we observed were in the lower sections of tributary streams. In general the flannelmouth sucker spawning period extends from March to late May in the Grand Canyon area. On February 29, 1976 reproductive condition of the flannelmouth sucker was checked at the mouth of the Paria River. Male individuals var- ied from a silvery color to orange-salmon color on body and fins. The silvery colored (prenup- tial) individuals had slightly developed tuber- cles. Those males with orange-salmon breeding color had moderately developed breeding tubercles. A few of these males were ripe, i.e., they voided milt upon slight pressure but none was "running" ripe. Most females were robust but none was ripe. The paria River was 13.50C and the main Colorado River just off the mouth of the paria was 70C. The Paria is invariably turbid and thus precludes direct observations. On April 3, 1976 collections and observations were made at the paria River. The paria at the cOllecting site was 180C and the main Colorado was 8.50C. One "running" ripe male Catostomus lati- pinnis was collected. It had well developed tuber- cles. Non-ripe females were collected although most had bright orange-tangerine color on lower fins including lower half of caudal fin. Two ripe male flannelmouth suckers were collec- ted on AprilS, 1976 from the paria River. These two males had better developed tubercles than the non-ripe males. No ripe female was taken al- though most specimens had moderately developed breeding colors. Two females were blackish or grayish without any orange coloration. The Paria