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164 VALDEZ AND MUTH Narrow and lower Cataract canyons (Holden and Stalnaker 1970, 1975a; Valdez 1990). Humpback chub evolved in seasonally warm and turbid water and is highly adapted to extreme hydrologic conditions (Valdez and Carothers 1998). Although not a strong swimmer (Bulkley et al. 1982), the species is extraordinarily special- ized for life in torrential water of canyon-bound reaches with a fusiform body, expansive fins, en- larged stabilizing nuchal hump, coarse skin, deeply embedded scales, and small eyes. Adults and juve- niles in the upper basin occupy deep eddies and pools along rocky shores, and young use sheltered shorelines and low-velocity habitats (Valdez and Clemmer 1982; Karp and Tyus 1990a; Valdez et al. 1990; Chart and Lentsch 2000). Humpback chub move substantially less than other Colorado River native fishes and exhibit strong fidelity for restricted reaches of river, generally less than 2 km (Valdez and Clemmer 1982; Kaeding et al. 1990; Valdez and RyelI997). Humpback chub mature in 2-3 years at 200 mm TL, and average fecundity is about 2,500 eggs per female (Hamman 1982). Spawning occurs dur- ing spring runoff at water temperatures of 16- 220C on large cobble bars or shorelines (Valdez and Clemmer 1982; Kaeding et al. 1986; Tyus and Karp 1989; Karp and Tyus 1990a; Valdez and Williams 1993). Larvae hatch at 18-21 oC in about 6 d (Muth 1990) but do not drift extensively and use shorelines close to natal areas. Humpback chub feed opportunistically on drifting food entrained in recirculating eddies, as well as invertebrates or detritus on the river bottom, including planktonic crustacea, larvae ofblackfly (simulid) and midges, filamentous green algae (primarily Cladophora glomerata), aquatic invertebrates, terrestrial inver- tebrates, and occasionally other fish and reptiles (Minckley 1973; Kaeding and Zimmerman 1983; Kubly 1990; Valdez and RyelI997). They become engorged by feeding on emergences of aquatic in- sects (e.g., mayfly hatches), grasshopper infesta- tions, or migrations of Mormon crickets (Tyus and Minckley 1988). Parasites include the external parasitic copepod Lernaea cyprinacea and Asian tapeworm Bothriocephalus acheilognathi (Brouder and Hoffnagle 1997; Clarkson et al. 1997). Bony tail Bony tail attain a maximum size of550 mm TL and 1,100 g (Vanicek 1967). Originally collected and described from the Zuni River, New Mexico (Sitgreaves 1853; Girard 1856), the species is com- monly called "bonytail chub," a name that has also been applied to humpback chub and roundtail chub and led to taxonomic confusion. Bony tail are streamlined with a small head, slender body, and thin caudal peduncle. Maximum age of fish from the Green River was 7 years (Vanicek 1967), and bonytail from Lake Mohave in the lower basin were 32-49 years (Ulmer 1983; Rinne et al. 1986). Bonytail was listed as federally endangered in 1980 (45 FR2771O) with critical habitat designated in 1994 (59 FR 13374). A recovery plan was ap- proved in 1984 (U.S. Fish and Wildlife Service 1984), revised in 1990 (U.S. Fish and Wildlife Ser- vice 1990b), and amended and supplemented with recovery goals in 2002 (U.S. Fish and Wildlife Ser- vice 2002c). Bony tail was once reported from various re- gions of the Colorado River system (Cope and Yar- row 1875; Jordan 1891; Jordan and Evermann 1896; Gilbert and Scofield 1898; Kirsch 1889; Chamberlain 1904). The species experienced an apparently dramatic but poorly documented de- cline starting in about 1950 that was attributed to construction of main-stem dams, introduction of nonnative fishes, poor land-use practices, and de- graded water quality (Miller 1961). Its population trajectory over the past century is unclear because of a lack of quantitative, historic basin-wide fishery investigations. Interchangeable nomenclature be- tween "bonytail" and sympatric Gila species (Valdez and Clemmer 1982; Quartarone 1995) has also led to confusion in species status. Ellis (1914) syn- onymized bonytail with roundtail chub ':..since in- termediate forms and those agreeing with the de- scriptions of both species were taken from the same station in the Grand [Colorado] River at Grand Junction. " The first record of bonytail from the upper basin was "One specimen taken in the Gunnison at Delta; five in the Green River... " (Jordan 1891; Bookstein et al. 1985). Gaufin et al. (1960) and Smith (1960) reported bonytail from Hideout Can-