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ENDANGERED SPECIES 369 Figure 15.3 Razorback sucker. (Photograph courtesy of E. Wick.) the primary refugium of the endangered Owens pupfish and Owens tui chub, was saved from development by a 1982 Act of Congress which allowed a land exchange between the Bureau of Land Management and a developer (Pister 1985). What remains of the native fishes of Death Valley? Of the endemic Owens River fishes, the Owens pupfish was nearly wiped out, speckled dace populations were greatly diminished, and tui chub hybridized with bait minnows (Pister 1974). Only the Owens sucker was largely unaffected. In Ash Meadows, interactions with introduced fishes led to extinction of the Ash Meadows killifish, Raycraft Ranch killifish, and Pahrump Ranch killifish. The Pahrump killifish survives perilously close to extinction in artificially maintained refugia. where it is threatened by bullfrogs and introduced fishes. The Ash Meadows speckled dace and Ash Meadows Amargosa pupfish were seriously threatened by groundwater pumping (Ono et al. 1983). Of the native fishes of Death Valley, Mohave tui chub, Owens tui chub, Ash Meadows speckled dace, Devils Hole pupfish, Owens pupfish, Ash Meadows Amargosa pupfish, and Pahrump killifish are endangered. Recent habitat preservation measures lead one to limited optimism about their future, but most native fishes of Death Valley remain endangered in every sense of the word. Ono et al. (1983) noted that 70% of the fishes on federal threatened and endangered lists were from desert environments. 15.4.4 Colorado River Basin Fishes The indigenous fish fauna of the Colorado River basin includes some of the most unique freshwater fishes in North America. Because the basin has been isolated for millions of years, its native fishes are morphologically different and evolution- arily and geographically distant from their nearest relatives. In terms of number of species or subspecies, cyprinids, catostomids, and cyprinodontids head the list of native fishes. Among the better-publicized natives are the Colorado squawfish, a large predatory minnow, and humpback chub and razorback sucker (Figure 15.3), both distinguished by a prominent dorsal hump at the nape. In all, about 54 fishes (presently recognized species and subspecies) are native to the basin, and most (83% of the total number) are also endemic. Stanford and Ward (l986b) and Carlson and Muth (1989) summarized information on within-basin distributions of native fishes. Because of severe abundance and range reductions, most native fishes of the Colorado River are currently in jeopardy. Two are extinct (Pahranagat spinedace .............