Devils River Minnow

Dionda diaboli

Description

The Devils River minnow is a small fish, with adults reaching a body length of 1.0-2.1 in (25-53 mm). It has a wedge-shaped spot near the tail and a pronounced lateral stripe with double dashes extending through the eye to the snout but not reaching the lower lip. The species has a narrow head with prominent dark markings on scale pockets above the lateral line; this produces a cross-hatched appearance when viewed from the top.

Behavior

The Devils River minnow is thought to feed primarily on algae. It is probably a broadcast spawner, with externally fertilized eggs that sink to the bottom substrate for untended incubation.

Habitat

The Devils River minnow occurs in stream habitat characterized by channels of fast-flowing, spring-fed waters over gravel substrates. It occurs in junctions where spring flow enters a stream, rather than in the spring outflow itself. Its habitat is periodically subjected to extreme water-flow variations caused by extended drought and flash floods. The general landscape is semi-desert.

Distribution

The Devils River minnow is a local (or endemic) species that is only known from three locations in Val Verde and Kinney Counties, Texas, and one in Coahuila, Mexico. It is native to tributary streams of the Rio Grande in Val Verde and Kinney Counties, Texas, and Coahuila, Mexico.

Threats

The Devils River minnow is part of a unique fish community and ecosystem of the Chihuahuan Desert of Mexico and Texas that contains a large number of threatened species. About half of the native fishes of that ecosystem are considered threatened and at least four species are recently extinct, mostly because of habitat destruction and the effects of introduced species of fish. The specific range of the Devils River minnow has been reduced and fragmented through habitat destruction caused by the construction of dams, the dewatering of springs, and other causes of ecological degradation. The population size at known critical habitats has declined greatly. In 1989, only seven individuals were collected from five sites at 24 sampling locations within the historical range of the species. The Devils River minnow was once one of the most abundant fish in the Devils River, but is now one of the least abundant. The status of the Devils River minnow in Mexico is not known for certain, but it is thought to be greatly reduced there. The decline of the Devils River minnow in its surviving habitats is likely due to unsustainable predation by introduced smallmouth bass (Micropterus dolomieu ), a game fish. Areas where the Devils River minnow occurs are mostly privately owned. Exceptions include the Devils River State Natural Area located north of Dolan Falls and managed by the state of Texas, and land adjoining portions of San Felipe Creek owned by the City of Del Rio. The Nature Conservancy, a private environmental organization, owns the Dolan Falls Preserve, in the middle portion of the Devils River. Primary land uses within the water-sheds supporting the Devils River minnow are cattle, sheep, and goat ranching.

Conservation and Recovery

The Devils River minnow is listed as a threatened species by the U. S. Fish and Wildlife Service (FWS), by the State of Texas, and by the government of Mexico. A Conservation Agreement in support of protection and management for the Devils River minnow has been signed between the FWS, the Texas Parks and Wildlife Department, and the City of Del Rio. This action has resulted in the implementation of protection and habitat management for the rare fish. Actions to be implemented in support of this minnow include: surveys and monitoring of its populations; maintenance of a genetically representative captive population at two fish hatch-ery facilities, for use in captive propagation to provide stock for reintroduction efforts and as insurance against extinction; establishment of new populations through reintroduction; protection of the San Felipe Creek watershed by the City of Del Rio; provision of technical assistance to landowners on riparian protection and management; review of live-bait harvest and selling practices in the Devils River area to develop a strategy to prevent the take of threatened species and introduction of non-native ones; studies of the abundance and range of exotic fish in the Devils River, and in San Felipe, Las Moras, and Sycamore creeks; studies of hydrology in critical habitats; and studies of the biology and habitat needs of the Devils River minnow, including interactions with the smallmouth bass.

Contacts

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/

U. S. Fish and Wildlife Service
Austin Ecological Services Field Office
Harland Bank Building
10711 Burnet Road, Suite 200
Austin, Texas 78758-4460
Telephone: (512) 490-0057

Reference

U. S. Fish and Wildlife Service. 20 October 1999. "Endangered and Threatened Wildlife and Plants: Final Rule To List the Devils River Minnow as Threatened." Federal Register 64 (202):56596-56609.