Endangered and Threatened Wildlife and Plants; Listing Gila Chub as Endangered With Critical Habitat

We, the U.S. Fish and Wildlife Service (Service), list the Gila chub (Gila intermedia) as endangered with critical habitat under the Endangered Species Act of 1973, as amended (Act). Gila chub were historically found throughout the Gila River basin in southern Arizona, southwestern New Mexico, and northeastern Sonora, Mexico. The Gila chub has been reduced in numbers and distribution in the majority of its historical range (Minckley 1973; Weedman et al. 1996). Where it is still present, populations are often small, fragmented, and at risk from known and potential threats and from random events such as drought, flood events, and wildfire. The primary threats to Gila chub include predation by and competition with nonnative organisms, including fish in the family Centrarchidae (Micropterus spp., Lepomis spp.), other fish species, bullfrogs (Rana catesbeiana), and crayfish (Orconectes virilis), and habitat degradation from surface water diversions and ground water withdrawals. Secondary threats include habitat alteration, destruction, and fragmentation resulting from numerous factors that are discussed in this final rule. The current status of the Gila chub is much degraded from historical levels. The species exists as a few, small isolated, populations. The small size of these populations, and their degree of fragmentation and isolation, cause them to be highly susceptible to threats. We believe that due to the current reduced status of the Gila chub and the severity of threats, including nonnative species predation and habitat destruction, the Gila chub is likely to become extinct throughout all or a significant portion of its range. This final rule will implement the Federal protection and recovery provisions of the Act for this species. We are also designating approximately 160.3 river miles (mi) (258.1 kilometers (km)) of critical habitat located in Grant County, New Mexico, and Yavapai, Gila, Greenlee, Graham, Cochise, Santa Cruz, Pima, and Pinal Counties in Arizona.