Laserfiche WebLink
<br />INTRODUCTION <br />The ichthyofauna of the present-day Colorado River mainstream is a unique <br />assemblage predominated by naturalized populations of non-native species (Minckley <br />1978, U.S. Fish and Wildlife Service [USFWS] 1980). In the lower river (below Grand <br />Canyon) the entire freshwater fish fauna has been essentially replaced, including five, <br />large-bodied endemic species, wild populations of which either are. extirpated <br />(humpback chub [Gila cypha], Colorado squawfish [Ptychocheilus lucius] and <br />flannelmouth sucker [Catostomus latipinnis]'), or severely depleted in numbers and <br />reduced in range (bonytail [Gila elegans] and razorback sucker [Xyrauchen texanus]) <br />as a result of human development of water resources'. These fishes once were widely <br />distributed and abundant (Minckley 1973, 1991), but all except flannelmouth sucker <br />now are federally- listed as endangered (U.S. Fish and Wildlife Service [USFWS] 1974, <br />1980, 1991), with critical habitats that include portions of the lower Colorado River <br />mainstream (USFWS 1994). <br />The largest known populations of bonytail and razorback sucker occupy Lake Mohave <br />(Marsh and Minckley 1992, Marsh 1994), a mainstream reservoir impounded across the <br />' Populations of humpback chub and flannelmouth sucker persist in the main <br />stream and major tributaries in Grand Canyon (Douglas and Marsh 1996, in press). <br />Flannelmouth sucker also occupies Virgin River, tributary to Lake Mead, and a stocked <br />population is in the river reach below Davis Dam. Both these fishes, plus Colorado <br />squawfish, still are found in larger streams of the upper basin (Carlson and Muth 1989). <br />2 Woundfin (Plagopterus argentissimus) now is restricted to the Virgin River (AZ- <br />NV-UT) and desert pupfish (Cyprinodon macularius) is represented in the United States . <br />by a few, scattered natural populations. Both of these endangered species are <br />extirpated from the lower Colorado River. Bluehead sucker (Catostomus discobolus), <br />speckled dace (Rhinichthys oscu/us), and roundtail chub (Gila robusta) also were <br />present, but rare (Minckley 1973), and are not further considered herein.