Barton Springs Salamander
Barton Springs Salamander
|April 30, 1997
|Plethodontidae (Lungless Salamander)
|Slender salamander with slightly elongate limbs and reduced eyes; color varies from pale purplish-brown to gray or yellowish-cream.
|Barton Springs, Texas.
|Amphipods and other small invertebrates.
|Breeds year-round; lays eggs underground.
The Eurycea sosorum (Barton Springs salamander) was first collected from Barton Springs Pool in 1946, was recognized in 1978 as distinct from other central Texas Eurycea salamanders based on its restricted distribution and unique morphological and skeletal characteristics (such as its reduced eyes, elongate limbs, dorsal coloration, and reduced number of presacral vertebrae), and was given formal description based on genetic studies in June 1993. The Barton Springs salamander is entirely aquatic and neotenic (meaning it does not metamorphose into a terrestrial form and retains its bright red external gills throughout life) and depends on a constant supply of clean, flowing water from Barton Springs. Adults attain an average length of 2.5 in (6.35 cm). This species is slender, with slightly elongate limbs and reduced eyes. Dorsal coloration varies from pale purplish-brown or gray to yellowish-cream. Irregular spacing of dorsal pigments and pigment gaps results in a mottled, "salt and pepper" pattern.
The Barton Springs salamander appears to be primarily a surface-dwelling species that retreats underground to lay eggs and to weather unfavorable conditions such as drought; its diet is believed to consist almost entirely of amphipods (Hyallela azteca ) and other small invertebrates. Primary predators of the Barton Springs salamander are believed to be fish and crayfish. Observations of larvae and females with eggs indicate breeding occurs year-round. The Barton Springs salamander's eggs are white and have never been observed in the wild. The salamander is vulnerable to declining water quality and quantity and other forms of habitat modification.
The Barton Springs salamander is known to only inhabit Barton Springs, the fourth largest spring in Texas. The water that discharges at Barton Springs originates from the Barton Springs segment of the Edwards aquifer. The Barton Springs segment covers roughly 155 sq mi (400 sq km) from southern Travis County to northern Hays County, Texas. The watersheds of the six creeks upstream (west) of the recharge zone span about 264 sq mi (680 sq km). This area is referred to as the contributing zone and includes portions of Travis, Hays, and Blanco Counties. The recharge and contributing zones, known as the Barton Springs watershed, make up the total area that provides water to the aquifer, which equals about 354 sq mi (920 sq km).
The Barton Springs salamander is found near three of four hydrologically connected spring outlets that collectively make up Barton Springs. These three outlets are known as Parthenia, Eliza, and Sunken Garden, and they occur in Zilker Park, which is owned and operated by the City of Austin.
The area around Parthenis Springs, the main spring outlet, was impounded in the late 1920s to create Barton Springs Pool, while flows from Eliza and Sunken Garden springs are also retained by concrete structures and form small pools located on either side of Barton Springs Pool. The salamander has been observed at depths of about 0.3-16 ft (9-500 cm) of water under gravel and small rocks, submerged leaves, and algae; among aquatic vegetation; and buried in organic debris. It is generally not found on exposed limestone surfaces or in silted areas.
No other species of Eurycea is known to occur in this portion of the aquifer. Although the extent to which the Barton Springs salamander occurs in the aquifer is unknown, it is likely concentrated near the spring openings where food supplies are abundant, water chemistry and temperatures are relatively constant, and where the salamander has immediate access to both surface and subsurface habitats. Barton Springs is also the main discharge point for the entire Barton Springs segment, and is one of the few perennial springs in the area.
No evidence exists that the range of the Barton Springs Salamander has ever extended beyond the immediate vicinity of Barton Springs in Zilker Park, Austin, Travis County, Texas. The species was reported to be abundant among the aquatic vegetation in the deep end of Barton Springs Pool during the later 1940s. The Barton Springs Salamander's numbers appear to have declined sharply in recent years. The first comprehensive surveys conducted in Barton Springs Pool a week apart in November 1992 counted 80 and 150 individuals. A comprehensive survey done immediately after an October 1994 flood reported a total of 16 salamanders, while only 10 were counted in March 1995. In June 1993, the City of Austin began monthly surveys that produced counts ranging from one to 27 individuals for the period between July 1993 to March 1995 and from three to 45 individuals between April 1995 to April 1996. Where "dozens or hundreds" of individuals were estimated to occur among sunken leaves in Eliza Pool during the 1970s, surveys in the late 1980s and mid-1990s variously reported zero to 28 living individuals. The salamander was first observed at Sunken Garden Springs in January 1993. Less than 20 individuals have been reported on any given visit to that outlet. Because it is part of the Barton Springs complex and is hydrologically connected to Parthenia Springs, biologists had speculated that the salamander occurred at Sunken Garden Springs, though it had not been observed in surveys conducted there between 1987-1992. Low water levels and the presence of large rocks and sediment make searching for salamanders difficult at Sunken Garden Springs.
The primary threat to the Barton Springs salamander is degradation through urban expansion of the quality and quantity of water that feeds Barton Springs. Urbanization dramatically increases stormwater runoff as natural ground cover is lost to impervious paved surfaces. Greater stormflow increases the frequency and severity of flooding, while simultaneoulsy making water resources more susceptible to severe dwindling during drought conditions. Sediment from soil erosion constitutes the largest volume of pollutants in surface waters and is itself the biggest carrier of additional pollutants found in water, including suspended solids, nutrients, petroleum hydrocarbons, bacteria, heavy metals, volatile organic compounds, commercial solvents, fertilizers, and pesticides.
Groundwater contamination is also caused by highway construction, leaking septic tanks and pipelines, and petroleum storage tank releases.
Karst aquifers characterized by porous limestone like the Barton springs segment transport pollutants rapidly once contaminated runoff enters creeks and other recharge features. The Edwards aquifer is therefore one of the most sensitive in Texas to the groundwater pollution that very frequently accompanies rapid urban development. Because ground-water originating from Barton Creek remains in the aquifer for short periods before discharging at the springs, there is little time for attenuation of pollutants before discharging at Barton Springs. Amphibians are known to be very sensitive to environmental contaminants because of their semipermeable skin. The Barton Springs salamander lives at the main discharge point for the aquifer, is continuously exposed to the waters emanating from it, and its diminishing presence serves as an early warning sign of deteriorating water quality and quantity in the Barton Springs watershed, which is the primary source of drinking water for the city of Austin.
One of the most immediate threats to the Barton Springs salamander is siltation of its habitat, owing primarily to major highway and subdivision construction activities in the Barton Creek watershed. High levels of suspended solids, such as the ones that occurred for five months after the October 1994 flood, are very harmful to aquatic fauna; Barton Springs Pool had its lowest recorded population counts of the salamander during this period.
Sediments cover much of the bottom of Eliza Pool and Sunken Garden Springs, and the Barton Springs salamander is typically found in silt-free areas near the spring outlets.
Problems caused by increased habitat sediment loads for the salamander include loss of livable areas, asphyxiation through clogging of the gills, smothered eggs, reduced oxygen availability in the water, loss of spawning sites, and reduced light transmission for aquatic-plant photosynthesis that can damage the food chain.
Contaminants like petroleum hydrocarbons and heavy metals also bind readily to sediments, and they are especially toxic to Hyallela azteca, the primary food item of the Barton Springs salamander Chronic releases from underground storage tanks are a major source of ground-water pollution. Gasoline, diesel fuel, and other petroleum products are all toxic pollutants that can effect acquifiers very quickly, and lead is also a very dangerous component of petrochemical pollution. Sewage effluent may contain a host of dangerous chemicals, heavy metals, pesticides, fertilizers, nitrogen and phosphorus nutrients, inorganic acids, and microorganisms. Wastewater discharges have been identified as a primary cause of algal blooms, a recurring problem in both Barton Creek and at Barton Springs. Increased nutrients promote eutrophication of aquatic ecosystems, including the growth of bacteria, algae, and nuisance aquatic plants, and lowered oxygen levels. Leaking septic tanks and inadequate filtering in septic fields have also been identified as a major source of ground-water contamination.
An estimated 4,800 septic systems currently exist in the Barton Springs watershed and may contribute as much as 23% of the total nitrogen load to the aquifer. Because of the Barton Springs salamander's limited range, a single catastrophic spill has the potential to impact the entire species and its habitat. Catastrophic spills can result from major transportation accidents, underground storage tank leaks, pipeline ruptures, sewage spills, vandalism, and other sources.
Increased demands on water supplies from the aquifer reduce the quality and quantity of water in the Barton Springs segment and at Barton Springs. The volume of springflow is regulated by the level of water in the aquifer. Spring discharge decreases as water storage in the aquifer drops; when water storage drops, the potential for "bad water" intrusion to the aquifer increases markedly. In addition to contributing to declining groundwater supplies, water wells often are a major source of groundwater contamination because they provide pollutants direct access into the aquifer. Reduced groundwater levels exacerbate the problem through decreased dilution of pollutants.
Other potential impacts to the salamander's surface habitat may include the use of high pressure fire hoses in areas where the salamander occurs, hosing silt from the shallow end of Barton Springs Pool into the salamander's habitat, diverting water from Sunken Garden Springs into Barton Creek below Barton Springs, and runoff from the train station above Eliza Pool.
Conservation and Recovery
The long-term survival of the Barton Springs salamander can only be ensured by preserving the health of the Edwards aquifer and the Barton Springs complex. This can only be done through an organized, concerted, and disciplined effort by all affected Federal, State, and local governments and the private citizenry to protect the Barton Springs watershed. This united action is necessary because, aside from the potential for catastrophic spills, it is the accumulated burden of many smaller developmental activities and water withdrawals that threaten the habitat of the Barton Springs salamander. Conservation of this species entails removing threats to its survival. These include protecting the quality and quantity of springflow from Barton Springs by implementing comprehensive management programs to control and reduce point and nonpoint sources of pollution throughout the Barton Springs watershed; minimizing the risk and likelihood of pollution events that would affect water quality; strengthening efforts to protect groundwater and springflow quantity; continuing to examine and implement pool cleaning practices and other park operations that protect and perpetuate the salamander's surface habitat and population; and public outreach and education. It is also anticipated that listing will encourage continued research on the critical aspects of the Barton Springs salamander's biology such as longevity, natality, sources of mortality, feeding and breeding ecology, and sensitivity to water contaminants.
The Service's original intention to list the Barton springs salamander as Endangered in 1996 was put aside because of a Conservation Agreement with various Texas agencies and authorities that would have increased protection for the salamander's habitat. This action was disallowed by a Texas court, and Fish and Wildlife Service was required to make a listing determination within thirty days; the court's decision on what was allowable information to consider and the limited time frame meant the Service had to make its determination without being able to examine all the information potentially available. During the comment period, the Service received written and oral comments, a majority of which supported the proposed action.
U. S. Fish and Wildlife Service
Ecological Services Field Office
10711 Burnet Road, Suite 200
Austin, Texas 78758-4460
Telephone: (512) 490-0057
U. S. Fish and Wildlife Service. 30 April 1997. "Final Rule To List the Barton Springs Salamander as Endangered." Federal Register 62 (83): 23377-23392.