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~-- ~, a~_ FII~~DINGS: COLOP~ADO RIVER IDIVESTIGATIONS Fishery Studies At the present time, 17 species of fish are known to occur in the Colorado River and its tributaries in the Glen Canyon area. It appears that the number of species of fish present in the Colorado River are rather re- stricted, while a more diverse fauna occurs in the tributary streams, (Tables 1 and 2). Fishery studies were conducted throughout the year, but the most intensive sampling was carried on during the summer of 1955• Although vela- tively complete collections were made in the tributary streams, the methods of collection utilized in the river were not altogether satisfactory,.:.,' This may account for the restricted number of~species collected from the main river channel. Generally, it appears that the species composition of the Colorado River is similar throughout the Glen Canyon area. Variations in numbers and species of fish were noted between the tributary streams. Same ponded, spring-fed streams, such as Warm Spring Creek and Aztec Creek, support a relatively large and diverse fish population, while others, such as the shallow and sandy- bottomed Escalante River, are virtually devoid of fish. There appears to be little seasonal variation in either the numbers or kinds of fish present, al- though periods of flash flooding or decreased stream flow doubtlessly cause temporary reduction in the fish population in sections of the tributaries. Age and growth information obtained from the various species of fish taken from the Glen Canyon area indicate that in most cases the growth rate is relatively slow (Table 3). This may be due to a multitude of factors, such as excessive stream fluctuation and the scouring action of the river. wring the summer of 1958, two species of fish were collected in the river which had not previously been known to occur in Utah. These were the Fathead minnox (P~ephales promelas) and the Southwest Plains Killifish (Fundulus zebrinus). The following fishes were found in the Glen Canyon area during the ccu rse of this investigation: Flannelmouth Sucker (Catostomus latipinnis). This fish was found to occur al- Chat exclusively in the river or backwaters and, with the exception of the nnel Catfish was the most abundant species in both the Colorado and San Juan Rivers. Stomach samples (Table 4) indicates that it feeds primarily on algae and other small organisms. The largest specimen collected was about 15 inches in length, Simon (1946) reports that spawning takes place in the spring. Colorado River Mountain Sucker (Pantosteus delphinus). This was exclusively a tributary form frequenting riffle areas. It was observed in limited