7984 - Laserfiche WebLink

Home Browse Search

CURRENT DISTRIBUTION AND ABUNDANCE The bonytail now is very rare. In the Lower Basin, individual fish still are taken occasionally by fishermen in Lake Havasu (USFWS 1990a). A few large, old adults also are still found in Lake Mohave, but no successful reproduction has been documented there. A total of 32 adult specimens was collected by biologists from Lake Mohave from 1974 to 1987, and several more were reported by anglers. An additional 16 fish were collected from Lake Mohave in 1988 and 1989 (USFWS 1990a). Recent distribution and abundance of the bonytail in the Upper Basin was described by Holden and Stalnaker (1975a), Tyus et al. (1982b, 1987), and Valdez and Clemmer (1982). Recruitment is apparently nonexistent or extremely low, with the most recent suspected juvenile bonytails originating only from the Desolation Canyon (Holden 1978) and Cataract Canyon areas (Valdez 1985). However, verifying recruitment is difficult due to the uncertainty that exists in the identification of juveniles. The bonytail was common in the Green River below the Yampa River confluence after Flaming Gorge became operational in 1962. Vanicek and Kramer (1969) reported large year classes in 1959, 1960, and 1961 based on the collection of fish longer than 8 inches TL during those years. Holden and Stalnaker (1975a) found 36 adults during a 4-year study of the Upper Basin, 29 of which were captured in 1968, three in 1969, and four in 1970. With the exception of two fish, all were collected in the Green and Yampa Rivers within Dinosaur National Monument. No young were identified during that study. Seethaler et al. (1979) sampled the Green and Yampa Rivers of Dinosaur National Monument in 1974-1976 and found no bonytail. Holden and Crist (1981) reported one adult 11 inches TL from the lower Yampa River in 1979. However, no specimens have been reported from there since (Tyus et al. 1982b, 1986). Miller et al. (1982b) reported no adult bonytail from Dinosaur National Monument in 1981-1983, and Wick et al. (1979, 1981) caught no adults and could not distinguish among larval Gila collected there. Although roundtail chub were found in the Green and Little Snake Rivers in Wyoming during a 1986 survey, no bonytail were captured (Johnson and Oberholtzer 1987). In other areas of the Green River, two bonytail adults were caught in Desolation Canyon in 1974 (USFWS 1990a; Paul Holden, BIO-WEST, pers. comm.). Holden (1978) caught one adult near Jensen, Utah, and one juvenile in Desolation Canyon in 1977. Several fish resembling bonytail were collected from Gray Canyon in 1980 and 1981 (Tyus et al. 1982a). During extensive sampling conducted in 1982-1985 in the Green River and a section of the Yampa River, one individual from Gray Canyon was tentatively identified as a bonytail from a total of 523 Gila specimens captured (Tyus et al. 1987). During the period 1977 through 1983, no bonytail were collected from the Colorado or Gunnison Rivers in Colorado or Utah (Wick et al. 1979, 1981; Valdez et al. 1982b; Miller et al. 1984). However, in 1984, a single bonytail was collected from Black Rocks on the Colorado River (Kaeding et al. 1986). Several suspected bonytail also have been captured in 33