7715 - Laserfiche WebLink

Home Browse Search

I I I I I I I I I I I I I I I I I I I PART I INTRODUCTION History II Bony tail II is the accepted common name for Gila eleQans(Robins et al. 1980). However, "bonytail chub II was used when the species was listed in 1980 and is the name commonly used by biologists in the Colorado River basin (Valdez and Clemmer 1982). Therefore, the term "bonytail chub" is used in this plan. The 'bonytail chub was listed as endangered by the U.S. Fish and Wildlife Service (Service) on April 23, 1980 (U.S. Fish and Wildlife Service 1980). Critical habitat for the species was not designated at the time of listing as it could not be specifically defined. Reproduction of this species has not been recently reported and ecological requirements are largely unknown; only incidental, large adult specimens have been positively identified in recent years. The recovery priority for the bony tail chub is ranked as 5C which indicates a high degree of threat and a low recovery potential for a species which is in conflict with some form of economic activity. General Description The bony tail chub was originally described by Baird and Girard (1853). The type locality was given as the Zuni River, New Mexico; however, Smith et al. (1979) suggested that the original specimens came from the Little Colorado River at the base of Grand Falls. The general description of the species has not changed significantly since 1853 although recent taxonomic clarifications have been attempted by Holden and Stalnaker (1970) and Smith et al. (1979). Bony tail chub, roundtail chub (~. robusta), and humpback chub (~. ~) are close relatives but may have developed different morphological adaptations presumably to the flow regimes of the mainstem rivers of the ~istoric Colorado River system. . Adult bony tail chub are gray or olivaceous on the back with silvery sides and a white belly. Breeding males have bright red-orange lateral slashes between the paired fins, a trait similar to other closely related chubs, and small tubercles on the head and anterior portions of the body. Breeding colors are more subdued and tubercles less well developed in females. A slight orange coloration is apparent at the base of the fins in both sexes throughout much of the year (Vanicek 1967). The bony tail chub generally reaches 300-350 mm (12-14 in.) iri total length but larger specimens of up to 600 mm (24 in.) have been taken from Lakes Mohave and Havasu on the lower Colorado River (Minckley 1973; W. Minckley, Arizona State University, pers. comm.). The adult bony tail chub has an elongated, somewhat laterally compressed body with a long, thin caudal peduncle (frontispiece). The head is small and has a somewhat oblique mouth. The skull is concave dorsally and, in adults, the head arches smoothly into a predorsal hump. Scales are often lacking or embedded on the top of the hump, belly, or caudal peduncle (Minckley 1973). The fins are large, with dorsal fin rays 9-11 (typically 10) and anal fin rays 9-12 (usually 10)