Yaqui Chub

Gila purpurea

Description

A medium-sized silvery minnow, the Yaqui chub, Gila purpurea, ranges in size from 5-6 in (12.5-15 cm). Its streamlined shape terminates in a narrow tail and V-shaped caudal (tail) fin. Dark-colored overall but lighter below, it displays a single dark band on its side, and a dark spot at the base of the tail. Fins are enlarged and nearly fan-shaped.

Behavior

This chub feeds on insects, arachnids, plant matter, detritus, and small fish. It uses backwaters of streams and springs beneath undercut and overgrown banks for feeding and shelter. Breeding behavior has not been described, but the fish probably spawns in deep pools, where there is aquatic vegetation. Spawning occurs in March. Males become steel-blue in coloration while females are straw-colored.

Habitat

The Yaqui chub requires clean, narrow, permanent streams and spring pools, free of introduced fishes. Streams typically consist of deep pools separated by riffles and flowing stretches of moderate current. The chub is associated with a variety of shrub and brush rangeland of the Rio Sonora Basin but prefers cut banks along pool margins, downed logs of mature trees, and rock overhangs in association with perennial flows. Larger individuals prefer deep pools and smaller individuals prefer intermediate riffles and smaller pools. The chub appears to inhabit deep pools and fast runs during floods and shallower isolated pools during dry seasons. Associated vegetation includes watercress, willow, seep-willow, cottonwood, velvet ash, and tobosa grass.

Distribution

This species is endemic to the Rio Yaqui basin of southeastern Arizona, northwestern Sonora, and portions of eastern Chihuahua, Mexico. This chub has also been recorded from the Rio Sonora and Rio Matape on the Pacific slope of Mexico. It was first collected from San Bernardino Creek, just south of the Arizona-Sonora border. The Yaqui chub survived in San Bernardino Creek in Arizona until spring flows diminished and the creek dried up. Remaining habitat was severely trampled by livestock seeking water, making it uninhabitable.

Surviving Arizona populations are known from a few springs on the San Bernardino National Wildlife Refuge and Leslie Creek in Cochise County. Contract biologists from the Arizona State University and the University of Michigan surveyed the Rio Yaqui basin in 1979 and found only a single chub, signaling a serious decline in numbers. The status of the Mexican populations is largely unknown beyond the fact that a severe decline in numbers has occurred. A large percentage of existing populations resulted from reintroductions, which have created large and viable stocks in diverse habitats throughout its historical range.

Threats

The range of the Yaqui chub decreased significantly because of habitat modifications, such as arroyo cutting, water diversion, dam construction, and excessive pumping of groundwater from aquifers. The American Fisheries Society proposed protection for the Yaqui chub as early as 1979, and in 1983 the Desert Fishes Council petitioned the U. S. Fish and Wildlife Service (FWS) to list the chub on the basis of its disappearance from San Bernardino Creek.

The U. S. Bureau of Land Management (BLM) has issued leases for geothermal resources on lands adjacent to the San Bernardino National Wildlife Refuge. Biologists fear that exploration and development of these leases could cause further depletion of the underground aquifers or create channels for pollution of groundwater. The BLM will examine these threats in consultation with the FWS.

Introduced predatory fishes, such as largemouth bass, bluegill, black bullhead, channel catfish, and green sunfish are present in some portions of the Rio Yaqui basin and probably feed on the Yaqui chub. Other springs and outflow streams within the San Bernardino National Wildlife Refuge may provide suitable habitat for the Yaqui chub. The FWS surveyed sites there in preparation for a translocation effort.

Many rivers in Mexico, formerly inhabited by the Yaqui chub, have been highly modified into an artificially channeled canal system to support irrigation agriculture. Water quality has declined drastically because of chemical and sewage contamination. The Yaqui chub receives no legal protection from the Mexican government.

Conservation and Recovery

Yaqui chubs from the Dexter National Fish Hatchery in New Mexico were stocked on San Bernardino Ranch in 1980, immediately following the purchase of the ranch by the Nature Conservancy. Two of three stockings succeeded. The Dexter stock failed in 1984 for unknown reasons and was immediately reinstated with 100 fish from the North Pond stock established in 1980. House Pond was renovated in 1984-85 to remove mosquitofish, a species incompatible with topminnows. It was re-stocked with chubs and topminnows in 1986. Also in 1986, because secure populations were established within the San Bernardino National Wildlife Refuge, Yaqui chubs were removed from the Dexter National Fish Hatchery and stocked in West Turkey Creek, where they established.

Yaqui chub reappeared in Black Draw in 1987, either from the 1980 stocking or through upstream dispersal from Mexico. Considerable FWS effort had by then been expended in erosion control and revegetation, and the positive results of this—coupled with consecutive wet years and the appearance of Mexican stone rollers (a cyprinid fish)—helped reestablish the Yaqui chub to its historic habitat.

Contact

U. S. Fish and Wildlife Service
Regional Office, Division of Endangered Species
P. O. Box 1306
Albuquerque, New Mexico 87103-1306
Telephone: (505) 248-6911
Fax: (505) 248-6915
http://southwest.fws.gov/

References

Hendrickson, D. A., et al. 1980. "Fishes of the Rio Yaqui Basin, Mexico and United States." Journal of the Arizona-Nevada Academy of Science 15 (3): 65-106.

Silvey, W. 1975. "Statewide Fisheries Investigations:Fishes of Leslie Creek, Cochise County, Arizona." Statewide Survey of Aquatic Resources, Federal Aid Project F-7-R-17. Arizona Fish and Game Department, Phoenix.

U.S. Fish and Wildlife Service. 1979. "Environmental Assessment of the Proposed Land Acquisition of San Bernardino Ranch, Cochise County, Arizona." U. S. Fish and Wildlife Service, Albuquerque.