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~7Jl qhSl J~1~ur~~~~: ~~.~~.~ ~I -rr ~ ~ lCf~;L .:\ tt~'dT~~~ clu.-\. FISHES OF THE UPPER COLORADO RIVER BASIN: DISTRIBUTION, ABUNDANCE, AND STATUS ':'J ., ) H.M. Tyus, B.D. Burdick, R.A. Valdez, C.M. Haynes, LA. lytle, and C.R. Berry ABSTRACT The distribution and relative abundance of fishes from the Upper Colorado River Basin are presented, by major tributary and reservoir. A total of 55 fishes are reported, of which 49 are primarily restricted to riverine habitat. Although 42 fishes are reported from reservoirs, only 6 species are primarily restricted to them. There are 42 exotic, 13 native, 8 endemic,l threatened, and 5 endangered fishes in the Upper Basin. Abundant species include 3 exotic and 3 native fishes; com- mon species included 4 exotic and 3 native fishes. Exotic species also include 24 classified as inciden- tal. Remnant populations of four threatened and endangered fishes are found in main-stem rivers of the Upper Colorado River Basin: Colorado squawfish lPtychocheilus Lucius), bony tail chub (Gila elegansJ, humpback chub (Gila cyphaJ, and razorback sucker (Xyrauchen texanus). Two other native fishes (subspecies) also exist in headwaters-the endangered Kendall Warm Springs dace rRhinichthys osculus thermalis) and the threatened Colorado River cutthroat (Salmo clarki pleuriticus). The threatened greenback cutthroat trout (Salmo clarki stomiasJ was designated as an exotic fish in the Upper Colorado River Basin. The federally protected endangered species appear to be further declining and there is no indica. tion that known sub-populations are increasing. The razorback sucker should be brought under federal protection as a threatened, or possibly an endangered. species. INTRODUCTION The Colorado River Basin (Frontis.) is predominantly arid to semiarid and is therefore limited in water resources. Water development has resulted in a significant demand for available water, and this demand is increasing with the need for more energy. Environmental alterations, including changing land and water use and the introduction of exotic species, have degraded the native fish fauna of the once-mighty Colorado River. Endemic fishes, uniquely adapted to the hostile river system in its unaltered form, are now exposed to new stress which threatens them with extinction. Although main stem rivers are still occupied by endemic fishes, historic ranges have been markedly reduced. This paper discusses distribution, abundance, and the present status of fishes of the Upper Colorado River Basin. It provides a base for documenting past and future changes of this highly variable river system. METHODS The Colorado River Basin is divided into Lower and Upper Basins near Lee Ferry, Arizona (Frontis). The Upper Basin is further divided into three major. systems, or hydrologic sub-basins: Green, Upper Main-stem and San Juan-Colorado (Fig. 1). Each ma- jor tributary consists of three aquatic zones (Joseph et aL 1977) - headwaters (upper zone), intermediate zone, and large river channels (lower zone). Fish distribution was mapped for the lower and in- termediate zones. Smaller coldwater tributaries of the upper zone were deleted from the base map throughout most of the basin because endemic fishes (with some exceptions) are absent in them. Reservoirs greater than 1,200 surface hectares are included. Also, hybrid fishes are listed but not in- cluded in distribution mapping. Every attempt has been made to obtain and pre- sent information acquired since 1977. although limited use was made of some 1975 data. Maps pre- sent current fish distribution, much of which is un- published. The relative abundance of native and exotic fishes is presented as: A = abundant - a species or subspecies occur- ring in large numbers and consistently collected in a designated area; C common - a species or subspecies occurring in moderate numbers, and frequently collected in a designated area; R rare - a species or subspecies occurring in low numbers either in a restricted area or having sporadic distribution over a larger area; or I incidental - an exotic species or subspecies occurring in very low numbers and known from only a few point collec- tions. A combination of shading, triangles, and circles was selected for distribution mapping. Circles are used only when more than one species is placed on one map. A series of triangles (or circles), closely spaced, indicates that a fish is rare. A single triangle 12