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~~~ Copeia, 1986(4), pp. 1021-1029 © 1986 by the American Society of~ Ichthyologists and Herpetologists .t RECENT CAPTURE OF A BONYTAIL (GILA ELEGANS) AND OBSERVATIONS ON THIS NEARLY EXTINCT CYPRINID FROM THE COLORADO RIVER.-The bonytail (Gila ele- gans) is one of several Gila endemic to the Col- orado River basin. The aquatic ecosystems of the basin have been profoundly altered by water- development projects, introduction of non-na- tive fishes, poor land-use practices and other activities of technologic man (Miller, 1961; Minckley and Deacon, 1968; Ono et al., 1983). The negative effects of these changes have pre- sumably been especially significant for the bonytail, for it is now near extinction. Observations of early workers indicate bony- tail were formerly widespread and abundant in the large rivers (Jordan, 1891; Jordan and Ev- ermann, 1896; Gilbert and Scofield, 1898). Vanicek and Kramer (1969) collected 67 bony- tail (> 200 mm TL) from the Green River dur- ing 1964-66 and were the last to report appre- ciable numbers in riverine habitat. During the past several years, fewer than ten presumed bonytail have been captured from the Green (Tyus et al., 1982 and references therein; Paul B. Holden, pers. com.) and about 25 bonytail have been collected from Lake Mohave, a lower Colorado River reservoir in which the few bonytail are large, old and apparently not re- producing (Minckley, 1983; Bozek et al., 1984). Because morphological characters do not clear- ly distinguish young bonytail from other sym- patric Gila, reproductive success of Green River bonytail is unknown. We document here the recent capture of a bonytail, describe the cap- ture site and other species that occur there and offer additional observations on the bonytail of the Colorado River basin. We captured a bonytail on July 17, 1984, from the Black Rocks area of the Colorado River, western Colorado. This 2 km long reach, a ma- jor habitat for humpback chub (G. cypha), is a narrow, deep-water, turbulent area formed by passage of the river through a relatively ero- sion-resistant layer of metamorphic rock. The Black Rocks area is unlike the broad, relatively shallow reaches of the nearby Gunnison and Green rivers from which bonytail historically were collected Qordan, 1891; Jordan and Ev- o ermann, 1896). We photographed the fish (Fig. 1), a mature female with light tubercles on pec- toral fins and head and took the following mea- surementsand counts (after Lagler et al., 1977) before releasing it alive: total length, 458 mm; fork length, 418 mm; weight, 560 g; distance between insertion of pectoral and pelvic fins, 86.6 mm; depth of nucha] depression (Smith et al., 1979), 6.7 mm; caudal-peduncle depth, 14.8 mm; caudal-peduncle length, 108.9 mm; head length, 85.8 mm; dorsal-fin base, 53.2 mm; anal-fin base, 55.2 mm; dorsal-fin rays, 10; and anal-fin rays, 10. These data and the photograph were provid- ed to six ichthyologists who have worked ex- tensively on the taxonomy of Gila and each was asked his opinion as to the identity of the fish. Four of five respondents agreed that the fish was a bonytail. The fifth believed the fish was largely bonytail, but that the ventral mouth overhung by the snout indicated the presence of some humpback chub genes. Two respon- dents mentioned the "Roman nose" or "flat head"-characters that could be interpreted as indicative of the occurrence of humpback chub genes-but the presence of these characters did not affect their identifications. One of these re- spondents suggested such characters reflect in- dividual variation that is especially pronounced among old fish. The bonytail was large and probably old. The largest seen by Vanicek and Kramer (1969) was 388 mm TL (estimated on the basis of scale annuli to be 7 yr old). Seven bonytail collected by Bozek et al. (1984) from Lake Mohave were 475-535 mm TL. The largest bonytail seen by Minckley (1973), from another lower Colorado River reservoir (Lake Havasu), was 489 mm TL. Although the age of that fish was not given, marks on otoliths of large bonytail from Lake Mohave suggested these fish might be more than 30 yr old (W. L. Minckley, pers. com.). Our capture demonstrates that bonytail re- main in the upper Colorado River basin, al- though their scarcity suggests a viable popula- tion might not exist. In addition to the bonytail, we collected 602 adult-size (>250 mm TL) Gila from the Black Rocks area; on the basis of gross morphologic characters, we tentatively identi- fied 272 as humpback chub, 271 as roundtail chub (G. robusta) and 59 as possible intergrades