Texas Blind Salamander

Typhlomolge rathbuni

Description

The Texas blind salamander, Typhlomolge rathbuni, is a smooth, unpigmented, sightless, cave-dwelling salamander that reaches a mature length of about 5 in (13 cm). This slender, frail-legged amphibian is white or pinkish with a fringe of blood-red, external gills. The head is large and broad; eyes are reduced (visible as two small dark spots deep beneath the skin); limbs are slender and long; four toes occur on the fore legs and five on the hind legs; snout is flattened.

Behavior

Observations on captive individuals indicate that the Texas blind salamander feed indiscriminately on small aquatic organisms and do not appear to exhibit an appreciable degree of food selectivity. Young T. rathbuni feed well on copepods. Larger salamanders are documented to eat amphipods, blind shrimp (Palaemonetes antrorum ), daphnia, small snails, and other invertebrates. Cannibalism has also been documented.

Due to the presence of juveniles throughout the year, the Texas blind salamander appears to be sexually active all year, which is expected since there is little seasonal change in the aquifer. Gravid females have been observed each month of the year. One gravid female contained 39 eggs. There appears to be a correlation between size (age class), number of testicular lobes, and number of times sperm has been produced.

The Texas blind salamander reproduced for the first time in captivity at the Cincinnati Zoo. Three different spawning events occurred between December 1979 and January 1980. Clutch size ranged from eight to 21 eggs per spawning. The eggs were unpigmented and were attached to pieces of gravel singly or in clusters of two or three eggs. Light intensity did not appear to affect embryonic development. However, relatively constant water temperature similar to that within the aquifer (69.8°F; 21°C) is necessary for normal egg development.

The Dallas Aquarium has also induced the Texas blind salamander to breed in captivity. Two individuals were apparently engaged in courtship behavior on May 11, 1994, and repeated this activity on May 15. The first clutch of 13 eggs was deposited singly on the limestone rocks in the aquarium on May 21 and 22. The eggs hatched within 12-16 days of oviposition, and the larvae began feeding within one month after hatching. Successful reproduction continues to occur at the Dallas Aquarium.

Habitat

The Texas blind salamander is an obligate troglobitic species that occupies the subterranean waters of the Edwards Aquifer in Hays County, Texas. It is neotenic (non-transforming) and aquatic throughout its life and lives in water-filled, cavernous areas in the San Marcos area of the Edwards Aquifer. Observations in caves with access to the water table indicate that this salamander moves through the aquifer by traveling along submerged ledges and may swim short distances before spreading its legs and settling to the bottom of the pool. Due to the relatively constant 69.8°F (21°C) temperature of subterranean waters in the Edwards Aquifer, the Texas blind salamander is believed to be adapted to this temperature regime and may be sensitive to changes in water temperatures. However, additional research is necessary to determine critical temperature minima and maxima for different life stages of this species.

Distribution

This species is endemic to the caverns of the Edwards Plateau in Hays County, Texas. All collections of sightings of the Texas blind salamander have occurred there. The species was previously known to occur in Wonder Cave but searches in 1977 did not locate any specimens. The total distribution for the salamander may be a small as 26 sq mi (67 sq km) in a portion of the Edwards Aquifer beneath and near the city of San Marcos.

Threats

The Edwards Plateau is located in the vicinity of San Marcos, halfway between Austin and San Antonio. For many years, water has been pumped from the aquifer to supply irrigation ponds and ditches. More recently, growth of the city of San Marcos and suburban development associated with Austin and San Antonio have placed heavier demands on the aquifer. Water levels have dropped appreciably and will probably continue to fall in the foreseeable future. Increasing development of the region threatens to pollute groundwater with sediments and sewage run-off.

Conservation and Recovery

Survival of this salamander and other endemic cave-dwelling creatures depends upon the stability and continued purity of the Edwards aquifer. The Nature Conservancy purchased Ezell's Cave in 1967. In 1972, Ezell's Cave was designated as a National Natural Landmark by the National Park Service, thus helping to preserve one of the species' historic habitats.

Personnel at the Cincinnati Zoo and the Dallas Aquarium have successfully propagated the species in captivity. The Dallas Aquarium is developing a captive breeding program for the species. The U. S. Fish and Wildlife Service (FWS) has recently provided funding for the collection and distribution to one or two additional facilities to increase the chances for successful captive propagation.

The 1996 San Marcos/Comal (Revised) Recovery Plan, which covers the Texas blind salamander and four other listed species, notes that recovery goals for the habitat's species include the survival of these species in their native ecosystems; the development of an ecosystem approach using strategies to address both local, site-specific and broad regional issues related to recovery; and the conservation of the integrity and function of the aquifer and spring-fed ecosystems that these species inhabit.

Delisting is considered unattainable for all five species (including the Texas blind salamander) due to the potential for extinction from catastrophic events. Consequently, the revised recovery plan calls for the establishment and continued maintenance of refugia capability for all five species in case of a catastrophic event.

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

Longley, G. 1978. "Status of the Texas Blind Salamander." Report No. 2. U. S. Fish and Wildlife Service, 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.

U. S. Fish and Wildlife Service. 1996. "San Marcos and Comal Springs and Associated Aquatic Ecosystems (Revised) Recovery Plan." U. S. Fish and Wildlife Service, Albuquerque.