Barton Springs of Zilker Park in Austin, Travis County, Texas. E. sosorum is restricted to and only found in two (Parthenia and Eliza) of the four hydrologically connected pools collectively named Barton Springs. E. sosorum is the only extant salamander species found in these two pools. No evidence exists that indicates E. sosorum is found anywhere else. This means that E. sosorum has the smallest habitat of any vertebrate in the world. (Chippindale et al 1993; Deanna Chamberlain, personal communication)

Biogeographic Regions: nearctic (Native )

endemic to a single state or province

United States

Origin: Native

Regularity: Regularly occurring

Currently: Present

Confidence: Confident

Type of Residency: Year-round

Global Range: (<100-250 square km (less than about 40-100 square miles)) Barton Springs, Edwards Aquifer, Austin, Travis County, Texas; occurs in three of four hydrologically connected spring outlets (see Chippindale et al. [1993] for further details). Barton Springs is fed by the Barton Springs segment of the Edwards Aquifer; this segment occurs in portions of Blanco, Hays, and Travis counties.

The average length of the Barton Springs salamander is 6.35 cm. The organism is small and is known for its fairly small head, reduced eyes (with a golden iris and black mottling), shovel-nosed snout, slender body and elongate limbs. E. sosorum has a very distinctive dorsal coloration known as the "salt and pepper" effect. Dorsal color varies in life from dark through medium gray to purplish gray or gray-brown to yellowish brown to yellowish cream. The varied degrees of blotched and mottled specks are attributed to an irregular mixture of (or lack of) melanophores, iridophores and pigment gaps. Overall, the mottled pattern gives the salamander olive brown specks with a base color of yellowish cream. The presence of silvery-white iridophores enhances the salamanders' luster. Some salamanders appear pale due to the lack of melanophores. The trunk of E. sosorum is finely speckled with melanophores while the ventral surface is creamy to translucent in color. Sometimes the stomach contents, as well as the presence of eggs in females, can be seen through the translucent skin. Dorsally, the limbs of E. sosorum, are unevenly speckled as well as the toes. Ventrally, the limbs are not speckled. In addition the relatively short tail of E. sosorum has an uneven distribution of melanophores. On the ventral surface of the tail the salamander has a narrow, orange-yellow strip from the posterior margin of cloacal vent to the tip. Furthermore, unique traits of barton spring salamanders include: three pairs of brightly-colored, red gills, four fingers on each hand, five toes on each foot and 16 pre-sacral vertebrae. These traits set Eurycea sosorum apart from other Central Texas Eurycea. (Petranka 1998; Deanna Chamberlain, personal communication; Chippindale et al 1993)

Length: 6 cm

Dorsal coloration is distinctive in most specimens; the combination of pigment gaps (pale areas due to an absence of melanophores) and frequently high concentrations of silvery-white dorsal iridophores apparently is unique (Chippindale et al. 1993). Slight "shovel-nose" evident in most specimens is not as extreme as in Tridentifera, but this characteristic does distinguish most individuals from members of surface populations that currently are assigned to Neotenes and E. NANA (Chippindale et al. 1993). Eyes are significantly reduced in comparison to individuals from other surface-dwelling populations of central Texas Eurycea; also, limbs of SOSORUM generally are proportionately longer (Chippindale et al. 1993). Eurycea sosorum typically has 16 presacral vertebrae, in contrast to the 17 typically present in surface-dwelling members of the Neotenes species group. Differs from other populations of central Texas Eurycea and TYPHLOMOLGE RATHBUNI also by a unique combination of alleles (see Chippindale et al. 1993).

• Freshwater

E. sosorum prefers clear waters and is mostly concentrated near the spring openings where food supplies are abundant, water chemistry and temperatures are constant and access to surface and subsurface habitats is available. Barton Springs salamanders are also found under rocks and gravel immediately adjacent to main spring outflows and within aquatic vegetation and algae mats. E. sosorum lives in water depths ranging from 0.1 to 5 meters. The springs where the salamanders are found flow year long and remain at a constant temperature of twenty degrees Celsius. E. sosorum in generally not found on exposed on limestone surfaces or in silted areas within the pools. Monthly population counts done by the city of Austin show that the Parthenia pool population may range anywhere from 90 - 150 salamanders and the Eliza pool has an average population of 30 salamanders. (Deanna Chamberlain personal communication; Rogers 1997)

Aquatic Biomes: rivers and streams

Comments: Spring dweller; occurs in the fourth largest spring in Texas; inhabited spring outlets are impounded/retained by concrete structures. Evidently, this species occurs primarily in nonsubterranean waters; unlikely to range extensively underground but can live in subterranean waters (Chippindale et al. 1993). Usually found under rocks or in gravel in about 0.1-5 m of water; also takes refuge among aquatic vascular plants, vegetative debris, and algae when such habitat is available (Chippindale et al. 1993). Spring habitat flows throughout the year and maintains a fairly constant temperature of 20 C. See Federal Register (17 February 1994, p. 7969-7970) for hydrological information on the Barton Springs segment of the Edwards Aquifer. Oviposition likely occurs in subsurface habitat (Federal Register, 4 September 1996, p. 46609).

Non-Migrant: Yes. At least some populations of this species do not make significant seasonal migrations. Juvenile dispersal is not considered a migration.

Locally Migrant: No. No populations of this species make local extended movements (generally less than 200 km) at particular times of the year (e.g., to breeding or wintering grounds, to hibernation sites).

Locally Migrant: No. No populations of this species make annual migrations of over 200 km.

The diet of E. sosorum consists primarily of the small invertebrate Hyalla azteca, an amphipod. E. sosorum also feeds on snails, crustaceans, black worms, leeches and bug larvae. In captivity the salamanders feed on earthworms, brine shrimp, white worms and commercial food pellets. Predators of E. sosorum are small fish and crayfish. (Deanna Chamberlain, personal communication; Bishop 1967; Rogers 1997)

Comments: Diet apparently consists almost entirely of amphipods and other small invertebrates.

Note: For many non-migratory species, occurrences are roughly equivalent to populations.

Estimated Number of Occurrences: 1 - 5

Comments: Only one occurrence.

Not many details of the reproduction of E. sosorum are known. This is due to the secretive and nocturnal nature of salamanders in general. In the wild, females have been found holding, at the maximum, forty eggs from September through January. It is known that females carry their eggs for a year before depositing them It takes one year for larvae to reach sexual maturity and all sexually mature individuals that have been found have been longer than 22.5 mm. Also in their native habitat, young hatchlings have been found in November, March and April. This evidence suggests that breeding takes place year round. In the wild, no deposited eggs have ever been found or seen. It is believed the E. sosorum may deposit it's eggs in the Edwards Aquifer which feeds the pools where they live. The Edwards Aquifer is a karst aquifer which means that it is very porous. Due to the small size of the salamander this hypothesis could be true. However, in captivity Barton Spring salamanders deposit their eggs on plastic plants in string-like clusters. The eggs are 1.5 mm in diameter and are surrounded by two jelly layers. They are easily observed because of their white color and iridiscent properties.

(Deanna Chamberlain, personal communication; Bishop 1967; Petranka 1998)

As of 1999, in captive-breeding programs, females have deposited eggs twenty times. Of the eggs deposited, larvae only developed twice and none survived to sexual maturity. What has been noted in the embryos is that after 19 days eyes develop and then, after 38 days, limb bud and gill structure is observed.

(Deanna Chamberlain, personal communication)

Recently hatched young have been found in November, March, and April, and females with well-developed eggs have been found from September through January; in captivity, one female retained well-developed eggs for over a year (Chippindale et al. 1993). Apparently breeds year-round.

• 1996
  Not Evaluated

Barton Springs salamanders have been proclaimed an endangered species by the U.S. Fish and Wildlife Service. E. sosorum was first found in Barton Springs during the 1940's, and numbered in the hundreds. However, in the past decade, fewer than 20 specimens were observed over six month periods and none at other times. In addition, the number of dead salamanders found was increasing. The drastic decrease in the E. sosorum population was credited to the decrease in water quality and quantity of the Edwards Aquifer and even more specifically the Barton Creek Watershed which feeds the aquifer. This decline is the result of increased urbanization and environmental pollution. Also, improper cleaning of the Parthenia pool of Barton Springs (used for recreational swimming) drastically disturbed the chemical and physical equilibriums of the salamanders' habitat. In the past two to three years environmental activists have petitioned for environmentally safer ways for cleaning the pool, bringing greatly needed attention to the water quality and quantity issues concerning Barton Springs as well as the Edwards aquifer. (Rogers 1997; Deanna Chamberlain, personal communication)

US Federal List: endangered

IUCN Red List of Threatened Species: vulnerable

United States

Rounded National Status Rank: N1 - Critically Imperiled

Rounded Global Status Rank: G1 - Critically Imperiled

Reasons: Occurs in spring outlets in only one location in Travis County, Texas; vulnerable to water contamination.

Intrinsic Vulnerability: Highly to moderately vulnerable.

Environmental Specificity: Very narrow. Specialist or community with key requirements scarce.

Degree of Threat: B : Moderately threatened throughout its range, communities provide natural resources that when exploited alter the composition and structure of the community over the long-term, but are apparently recoverable

Comments: Vulnerable to extinction due to very limited distribution within a sensitive habitat; primary threat is contamination of the waters that feed Barton Springs (see Federal Register, 17 February 1994, for detailed discussion). The Barton springs Aquifer has been designated by the Texas Water Commission as one of the aquifers most vulnerable to pollution in Texas (Chippindale et al. 1993). Excessive groundwater withdrawal is a potential threat. Under pool maintenance procedures in place as of 1992, human use of the Barton Springs Pool for swimming did not conflict with the continued existence of the salamander (Chippindale et al. 1993). Recreational swimming in the Barton Springs Pool does not pose a threat.

Management Requirements: Successful spawning of captives has been accomplished at the Dallas Aquarium and at the National Biological Service's Midwest Science Center in Missouri, but hatching success has been very low.

Global Protection: None. No occurrences appropriately protected and managed

Comments: Barton Springs is in Zilker Park, which is owned and operated by the City of Austin. City property is managed as a park and pool. Various agencies of the State of Texas have committed to expedite developing and implementing conservation measures needed for the species and the Barton Springs segment of the Edwards Aquifer, as set forth in the "Barton Springs Salamander Conservation Agreement and Strategy," signed 13 August 1996 (see Federal Register 61(172):46608-46616, 4 September 1996, for details). This agreement resulted in temporary USFWS withdrawal of proposed endangered status for this salamander.

Needs: Protect the single EO and its water supply (see "Barton Springs Salamander Conservation Agreement and Strategy").

Since the placement of E. sosorum on the U.S. ESA endangered species list, major restrictions have taken place on the urban development within the main watersheds of the Edwards Aquifer in Austin, TX. (Rogers 1997)

Comments: Sweet (1984) found this salamander to be structurally intermediate between Neotenes and Tridentifera. Chippindale et al. (1993, 2000) determined that this species is morphologically and biochemically distinct from all known species of plethodontids. Included in Neotenes by Brown (1950, 1967).