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F*Ishes of D*inosaur ROBERT RUSH MILLER, Ph.D. Curator of Fishes Museum of Zoology, University of Michgon Water suitable for fish life in Dinosaur National Monument is represented chiefly by the Green and Yampa rivers. There are few tributaries, and most of them carry water only in time of heavy rains. Conse- quently they do not provide a permanent home for these animals. An exception is Jones Creek, which flows into the Green from the north between Echo Park and Island Park. Chief interest in the fishes of the Monument lies in their remarkable adaptations to survive in a rather hostile environment. Conservation of these special- ized animals is therefore much to be sought after, since the native species are part of the unique herit- age of American wildlife which is losing ground against the advance of civilization. The Green and the Yampa form spectacular can- yons that slice through some of the most scenic landscapes to be found anywhere in the Colorado River country-the master stream to which the Green and Yampa rivers belong. This is rugged, breath- taking country and the silty rivers move now boister- ously over boulder-strewn rapids, now swiftly but silently through long, deep pools whose margins often abut against sheer cliffs stretching upwards as much as three thousand feet above the stream bed. In its 60-mile course through the Monument, the Green drops 650 feet, or an average of nearly f 1 feet per mile. In the steeper canyon sections, such as through Split Mountain, the grade rises to 21 feet to the mile. Formerly the water rushed along at speeds up to nearly 20 miles an hour, and flash floods raised the level of the Green 30 or more feet in very short periods. However, since November, 1962, when Flaming Gorge Dam (45 miles above the Monument) was closed, the Green River above its junction with the Yampa has had but a fraction of its former flow, its temperature (for some distance below the dam) is consistently cold enough for intro- duced trout, and it no longer exhibits spectacular rises and falls. These changes have affected the fish life but in just what way and to what extent has not yet been learned. Since the Green and Yampa rivers were extreme in many of their characteristics-great siltiness, wide variations in flow, and considerable temperature changes-the only fishes to survive in such an envi- ronment were those few that could adapt themselves to these extremes. About one-half of the species of fishes of Dinosaur National Monument have been introduced-some representing baitfishes and others game and food fishes. There are only eight native kinds, of which three were sought for food by the Indians and one- the Colorado squawfish-is regarded as a sport fish by present-day fishermen. Some of the introduced fishes-the rainbow trout and channel catfish, for example-have been in the region so long that many people living in Utah and Colorado do not realize that they did not always live there. Because of the heavy silt load of the Green River (and to a lesser extent of the Yampa), the only native trout of the Green River drainage-the cutthroat-never inhabited. the waters of Dinosaur National Monument; neither did the mountain whitefish (Prosopium williamsoni), a food fish abundant in higher parts of the Green River in Wyoming. In the following discussion of each species of fish now known to occur in the Monument, those that are not native are so indicated. TROUT FAMILY SALMONIDAE This family, which includes the whitefishes, trouts, charrs, salmon, and graylings, is widespread and numerous in northern parts of the world, where water temperatures are cold. They include some choice food and game fishes, of which the rainbow trout and brown trout have been successfully introduced into Dinosaur National Monument. RAINBOW TROUT, Salmo gairdneri Richardson This species is a very important game fish, having been planted in many parts of the world. Its original distribution was in those waters that flow into the Pacific from Alaska to northern Mexico (Baja Cali- fornia), excluding the Colorado River and its tribu- taries. Although this fish may survive waters that are warmer than 700 F., it prefers temperatures ranging from 55° to 650 F. The individuals in the Green and Yampa rivers, and tributaries such as Jones Creek, are maintained through stocking by the respective fish and game departments on a put-and-take basis. BROWN TROUT, Salmo trutta Linnaeus This European fish, which was first stocked in the United States in 1883, will stand higher tempera- tures than the rainbow trout and is more difficult to catch; it also averages larger-4 to 7 pounds versus 1 to 4 pounds. Since brown trout can live in warmer and less clear waters than other trout, they have been more common in the big rivers of the Monu- ment than has the rainbow. If the Green River clears and becomes consistently cold all the way to the Yampa as a result of the completion of Flaming Gorge Dam, the rainbow may supplant the brown in this region. 24 NATURALIST