Concho Water Snake

Nerodia paucimaculata

Description

The Concho water snake, Nerodia paucimaculata, rarely achieves a length of more than 3 ft (1 m). Its grayish upper surface is marked by four rows of irregular dark brown blotches arranged in alternate fashion along the top and sides. The Concho snake resembles its close relative, the Brazos water snake (N. harteri harteri ), except for details of coloration and patterning.

Behavior

This water snake feeds on minnows, frogs, toads, and small crustaceans.

Habitat

Adult snakes live in deep flowing water or in shallows where rocks and boulders provide secure hiding places. Woody vegetation along the stream banks is used for basking, while protected pools and rock piles provide suitable nesting sites. Immature snakes require stony-bottomed shallows and rocky banks.

Distribution

Arising in the uplands near Big Spring, Texas, the Concho River flows southeast through San Angelo before joining the Colorado River near the town of Concho. The Colorado River arises in the region south of Lubbock and winds west and south, passing through Austin on its way to the Gulf of Mexico. The Concho water snake once occurred over about 280 mi (450 km) of the Colorado and Concho rivers in west Texas.

This water snake now occurs in discontinuous localities along about 250 mi (400 km) of the Colorado and Concho rivers in central Texas, including parts of the river in ten counties: Brown, Coke, Coleman, Concho, Lampasas, McCulloch, Mills, Runnels, San Saba, and Tom Green. There is no current population estimate, but numbers have declined significantly and are considered low. Critical habitat for the snake was designated by the U. S. Fish and Wildlife Service (FWS) on June 29, 1989. Designated areas include the Concho River in Tom Green and Concho counties, Texas—a stretch extending from Mullin's Crossing, five miles northeast of the town of Veribest, downstream to the confluence of the Concho and Colorado Rivers; and the Colorado River in Runnels, Concho, Coleman and McCulloch counties, Texas—a stretch extending from the Farm to Market Road (FM) 3115 bridge near the town of Maverick, downstream to the confluence of the Colorado River and Salt Creek, northeast of the town of Doole. Also designated as critical habitat was the entire O.H. Ivie (formerly Stacy) Reservoir Basin up to the maximum water level of 1,551.5 feet abovesea level (472.8 meters above sea level [msl]) elevation including reservoir banks up to 15 vertical ft (4.8 m) above the 1,551.5 ft elevation.

Threats

The Concho water snake's habitat has been fragmented by the construction of four large-scale dams and reservoirs along the main rivers, plus several smaller impoundments on tributaries. Completed in 1968, the Robert Lee Dam on the Colorado River eliminated a large population of Concho water snakes along with 28 mi (45 km) of habitat. The newly constructed O.H. Ivie (formerly known as Stacy) Reservoir and dam on the Colorado River further segments the snake population. Dams inundate habitat upstream and alter water flow regimes downstream, leaving only isolated sections of river in a natural condition. Water snake populations are artificially separated and prevented from interbreeding, which further limits chances for survival. Diversion of water, primarily for irrigation, has reduced water levels and flows in some stretches of river. Increased sedimentation also occurs when water flow is reduced. In addition, water pollution has increased, mainly because of fertilizer, herbicide, and pesticide runoffs. The fate of the Concho water snake hinges on the politically divisive debate of habitat conservation versus access to water rights in a region where access to water often determines economic survival. Human population increases in the region demand the diversion of more water for residential and industrial use, which is causing a deterioration in the Concho water snake's habitat.

When the Concho water snake was first proposed for Federal Threatened status, many local residents expressed the opinion that listing the snake was a ploy by opponents of the Stacy Reservoir to halt construction. The FWS determined that the snake qualified for listing, even without considering the impact of the reservoir. The Colorado River Municipal Water District, sponsors of the Stacy Dam project

(now known as the O.H. Ivie Reservoir), agreed to restore and maintain important stretches of river habitat in exchange for construction permits. The entire O.H. Ivie Reservoir basin was designated a critical habitat for the snake in 1989.

Conservation and Recovery

According to the 1993 Concho Snake Recovery Plan, the snake will be considered for delisting (removal from Threatened status) when adequate in-stream flows are assured and stable, viable populations occur in all three main reaches of the snake's range—the Colorado River above and below Freese Dam, and the Concho River. Additionally, movement of an adequate number of Concho water snakes must be assured, as long as O.H. Ivie Reservoir exists, to counteract adverse effects of population fragmentation.

The plan calls for a variety of actions to meet these goals, including the elimination or reduction of threats to populations (including habitat degradation) through a variety of consultation, permitting and cooperative programs; the protection of stream flows in the Colorado and Concho rivers; and the reintroduction of Concho water snakes into suitable habitat in its historic range. If such actions are taken, the Recovery Plan predicts that the species may be eligible for delisting by 2005.

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

Flury, J. W., and T. C. Maxwell. 1981. "Status and Distribution of Nerodia harteri paucimaculata." Endangered Species Office, Albuquerque.

Scott, N. J., Jr., and L. A. Fitzgerald. 1985. "Status Survey of Nerodia harteri, Brazos and Concho-Colorado Rivers, Texas." Denver Wildlife Research Center, U.S. Fish and Wildlife Service, Museum of Southwestern Biology, Albuquerque.

U.S. Fish and Wildlife Service. 1987. "Endangered and Threatened Species of Texas and Oklahoma (with 1988 Addendum)." U.S. Fish and Wildlife Service, Albuquerque.