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164 DOUGLAS ET AL. FIGURE l.-Big-river Gila spp. from the Colorado Plateau of southwestern North America: G. robusta (top); G. elegans (middle); G. cypha (lower). 1989), or weak or inadequate analyses (Douglas 1993). Particularly problematic have been "big- river" chubs of the Colorado Plateau (i.e., hump- back chub G. cypha, bony tail G. elegans, and roundtail chub G. robusta; Figure 1). The ability of fishery biologists to morphologically discrim- inate these chubs has not markedly improved since the fish were initially described (reviewed by Douglas et al. 1989:654; Minckley 1996:18-22). If anything, it has worsened. In the last few de- cades, Colorado Plateau rivers have been behead- ed, diverted, or dammed for human uses (Fradkin 1984), thus eliminating or compromising realized niches of these species. Forms once allopatric are now often constrained into sympatry, confounding an already complex issue by markedly increasing potentials for hybridization. Ongoing studies of these forms are further impeded because of their endangered status (Douglas et al. 1989). Phenotypic variability in Gila has long been ig- nored by fishery managers in western North Amer- ica as inconsequential to the job of managing more profitable game fishes (Holden 1991). This bias not only retarded native fish management for de- cades but contributed greatly to the overall con- fusion surrounding the big-river chubs. Holden (1991) summarized (and interpreted) the philos- ophy of those times when he declared In the 1950s, two forms of bony tails (a common name then generally applied to Colorado River chubs) were taxonomically recognized as subspecies-roundtail chubs (G. r. robusta) and bony tail (G. r. elegans). A third form, the humpback chub (G. cypha) had only recently been described (Miller 1946) and did not yet enjoy general acceptance as a valid taxon. Thus, McDonald and Dotson (1960) reported collections from the Green River in Hideout Canyon in July 1959 that included 46 "bony tails, " but Smith (1960) re- ported these same collections to include 13 hump- backs and 36 bony tails. . . . Bosley (1960) recorded all the chubs he collected as "bony tails," to which he applied the name G. r. robusta, even though he mentioned that "there appears to be a change in the physical characteristics of this fish in the extreme low- er section of the study area," and presented photo- graphs that clearly included all three species. Mc- Donald and Dotson (1960) also acknowledged that several morphological variants existed, yet these re- searchers grouped all the fish into a single taxon since " "