|Listed||October 11, 1983|
|Description||Medium-sized, dusky brown chub.|
|Habitat||Deep pools in small streams.|
|Food||Insects, aquatic invertebrates, plant matter.|
|Reproduction||Spawns in April or May.|
|Threats||Water diversion, dam construction, pollution.|
|Range||New Mexico; Chihuahua, Mexico|
The Chihuahua chub, Gila nigrescens, is a medium-sized minnow, ranging from 3-6 in (8-15 cm) long. It is a dusky brown above and whitish beneath. During the breeding season an orange-red color develops around the mouth and lower fins. In the past, this species has also been variously classified as G. pulchella and Tigoma nigrescens. To add to the confusion, the name G. nigrescens has been applied by some authors to a different chub found in the Rio Grande and Pecos rivers.
The Chihuahua chub, like a trout, takes insects from the surface of the water. It feeds also on small, aquatic invertebrates, fish fry, and some plant matter. Chubs spawn in April and May over beds of aquatic vegetation in deeper, quiet pools. The habitat is subject to extreme drying in summer and violent flash floods in the rainy season. Seven centuries ago when the watershed was more stable, the Mimbres Indians took large numbers of these chubs for food and used the fish as a design element on their pottery.
This species inhabits smaller streams in canyon-lands. Average water depth is only about 3 ft (1 m), but the shallow stream beds are often interspersed with deeper pools. This chub prefers overhanging vegetation, undercut banks, or submerged trees for cover. Associated with the Chihuahua chub in some of the same streams is the Endangered beautiful shiner (Notropis formosus ).
The Chihuahua chub once ranged throughout the Guzman basin, which includes the Mimbres River of southwestern New Mexico and the Rio Casas Grandes, Rio Santa Maria, and Laguna Bustillos Rivers of Chihuahua, Mexico.
When surveys for the Chihuahua chub were conducted in 1979, one small, relict population of about 100 fish was found in the Mimbres River in Grant County, New Mexico. In 1981 and 1982 the New Mexico Department of Game and Fish discovered a second small population in the mainstream of the river. The presence of all age grades suggests that successful reproduction has continued despite severe flooding of previous years.
The Mimbres River of New Mexico has been significantly modified by agricultural and flood control developments. Chihuahua chub populations have declined because of the diversion of water for irrigation, dam and levee construction, and artificial stream channelization. The excessive pumping of groundwater has caused many springs in the region to dry up. These conditions have restricted the Chihuahua chub to one small section of the river. Continuing flood reclamation work, irrigation diversions, and channelization will undoubtedly contribute to further decline.
Water pollution has been responsible for eliminating the chub from most of its range in Mexico. Development of hydroelectric facilities, diversion of surface waters for irrigation, and excessive pumping from the underground aquifers have completely dried up many streams and springs in the region.
Conservation and Recovery
The delisting of this fish could only be considered when conservation easements are in place along the springfed headwaters of the river and two additional populations have been reestablished within its former range. The Chihuahua chub is currently being propagated at the Dexter National Fish Hatchery at Dexter, New Mexico, for use as rein-troduction stock.
Regional Office of Endangered Species
U.S. Fish and Wildlife Service
P.O. Box 1306
Albuquerque, New Mexico 87103
Hatch, M. D. 1980. "Management Plan for the Chihuahua Chub, Gila nigrescens (Girard, 1856), in New Mexico." New Mexico Department of Game and Fish, Santa Fe.
Hubbard, J. P., et al. 1978. Handbook of Species Endangered in New Mexico. New Mexico Department of Game and Fish, Santa Fe.
U.S. Fish and Wildlife Service. 1986. "Chihuahua Chub Recovery Plan." U.S. Fish and Wildlife Service, Albuquerque.