Bonytail

DESCRIPTION:
Bonytail are elongated and streamline. Adults have a concave skull and a pre-dorsal hump; and the mouth is terminal. The caudal peduncle is long and thin, its least depth 5.0 or more times into the head length. There usually are more than 90 (to more than 110) tiny scales in the lateral line, some deeply embedded, and with scant or absent basal radii. There are 10 or more dorsal fin rays, 10 anal fin rays, and 9 (sometimes) pelvic fin rays. The body color is silvery darker above and lighter below, white on belly. Breeding males are orange-to-red on the lower jaw and sides, and on paired and anal fin bases; they also develop fine tubercles on the head, body, caudal peduncle, and on the fins near the base. Pharyngeal teeth in two rows 2,5—4,2. Maximum length about 25 in (64 cm).

DISTRIBUTION & STATUS:
Bonytail is one of the “big river” fishes that once was common and widely distributed throughout the Colorado River basin of western North American including parts of Arizona, California, Colorado, Nevada, Utah, and Wyoming in the United States, and in the Colorado River delta in Baja California Norte and Sonora, Mexico. Wild Bonytail populations likely numbered in the hundreds of thousands in the mid-1990s, but today their are no known populations in the basin. Bonytail is one of the most critically imperiled vertebrate species in the United States. The few Bonytail individuals captured in the basin today are survivors released from hatcheries, but long-term survival of these stocked fish is immeasurably small. Water development, and introduction and establishment of non-native species resulted in widespread extirpation and declines in distribution and abundance of this and other native species beginning early in the 20th century, which culminated in its federal listing as endangered (U.S. Fish & Wildlife Service [FWS] 1980). The species status has deteriorated despite substantial recovery efforts.

HABITAT:
Bonytail are most common near heads of pools or in riffles. Large adults occupy very fast water and it has been reported that Bonytail occur principally in eddies and pools of the Green River, Utah. Young-of- Year (YOY) Bonytail in streams presumably behave similar to other chub species, moving to the margins to feed and grow, then progressively invading deeper and larger waters. Crowl et al (1995) in their laboratory studies found that individuals that have undergone three months of training in intermittent flow (0.07m/s) selectively inhabit higher velocities in stream channels and feed exclusively in high flow, high turbulent habitats. Bonytail that have undergone flow training spend a large proportion of their time near the substrate in high velocity and in high turbulent areas (Crowl et al 1995).

FOOD HABITS:
Bonytail diet consists largely of insects and other small animals. Adult Bonytail in the Green River feed primarily on terrestrial insects, plant debris, and algae with young feeding mostly on aquatic insects. Minckley (1973) found that in lakes, Bonytail feed on plankton and algae on the basis of a few stomachs examined. A few adults examined for food habits had eaten a high percentage of terrestrial invertebrates, drifting insects that had been blown by wind or otherwise fallen into the river. Occurrence of adult aquatic insects in stomachs also implies feeding on drifting organisms near the surface of the water.

REPRODUCTION:
Bonytail spawn in June and July. The only reproductive activities recorded for Bonytail are of aggregations of adults over gravelly "reefs" in artificial impoundments. Minckley (1973) observed spawning in reservoirs but no success was noted. Marsh (1985) reported the percentage hatch of Bonytail was highly dependent upon incubation temperature with statistically equivalent success (35 and 32%) at 15⁰ and 20 ⁰C, respectively. Time of peak hatch decreased with increasing temperature from 204 h at 15⁰C to 103 h at 20⁰C. Breeding males are orange-to-red on the lower jaw and sides, and on paired and anal fin bases; they also develop fine tubercles on the head, body, caudal peduncle, and on the fins near the base.