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ENDANGERED AND THREATENED FISH IN THE YAMPA AND GREEN RIVERS OF DINOSAUR NATIONAL MONUMENTl K.H. Seethaler, C.W. McAda, and R.S. Wydoski2 INTRODUCTION The Colorado River system of the western United States has been greatly modified during the past century, primarily by the construction of dams. The resulting alterations of the flow regimes and of water temperatures below these impoundments, and competition with introduced fish, are believed to be the major factors in the decline of four endemic Colorado River fish: Colorado squawfish, Ptychocheilus lucius; humpback chub, Gila cypha; bony tail chub, Gila elegans; and humpback sucker, xyrauchen texanus (Vanicek, Kramer, and Franklin 1970; Minckley 1973; Holden and Stalnaker 1975b). The first two species are officially designated as "endangered" by the U.S. Fish and Wildlife Service (1973); the other two were recommended for listing as "endangered" and "threatened", respectively, by the Desert Fishes Council in 1975. Other water development projects are in prog- ress or planned for the upper Colorado River basin. Crawford and Peterson (1974) noted that the Colorado River, the key to development of the arid southwestern United States, is probably the most utilized, controlled, and fought over river in the world. This river annually collects less water per square mile of drainage than any other major river in the United States, yet it serves 15 million people with water for cities, irri- gated agriculture, recreation, mining, and indus- try (Utah Water Research Laboratory 1975). This region contains some of the largest fuel depos- its (coal, oil, oil shale, uranium) in the United States, and water will be a principal factor in the development of these energy resources (Bishop, Chambers, Mace, and Mills 1975). Consequently, there is manifest pressure to proceed with fur- ther alteration of this already over-allocated water resource. More development will impose additional stress on the endemic fish fauna of this unique ecosystem. This summary of the current status Of threat- ened and endangered fish inhabiting Dinosaur National Monument is based on a literature review and current research by the Utah Cooperative Fishery Research Unit. DESCRIPTION OF THE AREA The upper Green and Yampa rivers originate as cold, clear streams "in the Rocky and Uinta moun- tains. These headwater streams supply the main tributaries of the Colorado River Basin that flow through deserts where spectacular canyons have lThis study was supported by U.S. Fish and Wildlife Service Contract No. 14-16-0008-1140. The funds that enabled the senior author to at- tend the First Conference on Scientific Research in the National Parks were granted by the Ecology Center, Utah State University, Logan. 2Utah Coo erative Fishery Research Unit, Utah State Univer~ 'ty UMC 52, Logan, Utah 84322. The Utah cooperat~ve Fishery Research Unit is jointly sponsored by \ e Utah Division of Wildlife Re- sources, Utah \ tate University, and the U.S. Fish and Wildlife S rvice. been carved by erosion of the soft sandstones. Historically, the main stems were warm and tur- bid and subject to sudden changes in volume and velocity. Flaming Gorge Dam, which was com- pleted in 1963 and is near the Utah-Wyoming bor- der, has changed the upper Green River. Flows that were characteristically high in spring and low in winter became much more stabilized sea- sonally, but may be subject to rapid daily fluc- tuations (Vanicek, Kramer, and Franklin 1970). Dinosaur National Monument is in northwestern Colorado and northeastern Utah (Fig. 1). The Yampa River empties into the Green River at Echo Park, about 105 kID below Flaming Gorge Dam, modi- fying and partly restoring the Green to preim- poundment conditions. For the next 42 kID, the Green River passes alternately through canyons and meandering flats until it opens upon the Wonsits Valley in the Uinta Basin at the Monu- ment's southwest boundary. At this point the river has largely recovered from the impact of Flaming Gorge Dam with respect to temperature and perhaps several other characteristics as well. We note, therefore, three distinct habitat types within the study area, plus one section in which there is a gradation between these types. The Green River above Echo Park - A cold- water environment under the artificial control of Flaming Gorge Dam. The Yampa River - Still a relatively free- flowing, warmwater river. The Green River below the Monument - A warm- water. river, largely recovered from the effects of Flaming Gorge Dam, extending downstream to the confluence of the Green and Colorado rivers in Canyonlands National Park, a distance of 550 kn,. The Green River between Echo Park and the lower Monument boundary - A region of gradation from a cold - to a warmwater environment, extend- ing about 42 km from the confluence of the Yampa and Green rivers downstream to the southwest boundary of the Monument. RESEARCH ON THE FISH FAUNA IN THE WATERS OF, AND ADJACENT TO, THE DINOSAUR NATIONAL MONUMENT In March 1963, Secretary of the Interior Stewart L. Udall requested that the Utah Coop- erative Fishery Unit conduct investigations to determine the extent of changes in habitat and fish populations that occurred in Dinosaur . National Monument after the closure of Flam~ng Gorge Dam. The conclusion of the 1963-1966 study was that the environment of the Green River was changed significantly from the dam to the mou~h of the Yampa River (Vanicek 1967). Below the~r confluence, the Yampa River, which had retained its natural character, moderated the altered Green River sufficiently to allow the continued existence of all species of fish present before impoundment. The large native fishes disap- peared from the 105 km reach below Flaming Gorge Dam because of the cold water discharge from the dam and were replaced by introduced rainbow trout 605