Jollyville Plateau Salamander

Eurycea tonkawae is a small, neotenic (never metamorphosing into terrestrial form) salamander that is completely aquatic throughout its life and retains its external gills. According to Chippindale et al. (2000), adult females have well-developed eyes, broad, jaws, and blunt snouts. Three pairs of filamentous external gills are located on either side of the neck, just behind the head. The dorsal color is a dark-greenish brown, while the ventral surface is translucent and unpatterned. The tail is long and slender, with bright orange well-developed fins.In 2005, the Save the Springs Alliance petitioned the U.S. Fish and Wildlife Service to list Eurycea tonkawae as an endangered species. The petition not only included the general natural history of this species, but also cited detrimental factors such as urbanization, contamination and degradation of water quality, and emphasized the necessity of adequate measures to ensure the survival of E. tonkawae. A review to determine whether the species needs Endangered Species Act protection is expected to be completed by December 2007 (Austin Chronicle 2007).

The distribution for this species is highly restricted. Eurycea tonkawae is found on the Jollyville segment of the Edwards Plateau, Texas, where it is endemic (Bowles et al., 2006).. Its range is limited to six stream drainages in northwestern Travis County and the borders of Williamson County, including Brushy Creek, Bull Creek, Cypress Creek, Long Hollow Creek, and Walnut Creek (Herbez 2005). Like other members of the genus Eurycea, E. tonkawae is confined to the proximity of springs, wet caves, and spring-dominated flows (City of Austin 2001). Eurycea tonkawae also inhabits water-bearing karst formations, shaped by dissolution of calcium carbonate from limestone bedrock. This creates a series of drainages, underground openings, fissures, and sinkholes. The typical habitat for this species is cool, shallow oxygenated water, usually no more than one foot deep (Bowles et al. 2006). Preferred substrates are usually loose, consisting of rubble, cobbles, boulders, or gravel (Herbez 2005).

Numbers of E. tonkawae are highest during spring and summer months (March to August), particularly juvenile salamanders. Average salamander densities are greater within undeveloped watersheds than in developed areas (Bowles et al 2006). Eurycea tonkawae primarily preys upon benthic macroinvertebrates such as chironomid larvae and amphipods (City of Austin 2001).

Being completely aquatic, E. tonkawae’s survival and abundance depends mainly upon water quality and other abiotic features of the aquatic environment. Several factors may explain the highly restricted distribution of the genus Eurycea, including minimal substrate siltation, alkalinity, calcium carbonate deposition, and thermal and temporal flow reliability (Tupa & Davis 1976). All of these factors are affected by urbanization, which is undoubtedly the biggest threat for E. tonkawae. Urbanization is rapid within Travis and Williamson Counties, and the localized habitats of E. tonkawae are highly vulnerable to droughts, draining, and contamination. Bowles et al. (2006) carried out salamander surveys at nine stream sites on Jollyville Plateau from December 1996 to December 1998 to assess the impacts of urbanization along these habitats. These nine sites were classified as either developed or undeveloped, depending upon the percentage of impervious cover (Bowles et al. 2006). Mean salamander densities were significantly lower within developed tributaries in relative to undeveloped tributaries. One reason for this difference may be higher water conductance. Another reason might be an increase in ion levels in surface water from Bull Creek and Barton Creek, which has been attributed to roadway runoff, fertilizer applications and wastewater line leaks (Johns 1994; Johns & Pope 1998). The City of Austin (2001) also reported that salamander densities were lower in areas with higher ionic constituents, including chloride, potassium, sodium, and sulfate. Amphibian eggs and larvae are highly sensitive to chemical runoff and pollutants, including pesticides, organophosphates, and petroleum hydrocarbons (USFWS 2002). The prey of E. tonkawae (amphipods and other crustaceans) are also highly susceptible to water pollution. Thus pollutant effects ranging from change of water chemistry to contaminated prey could potentially lead to developmental abnormalities, low reproduction, and overall reduction of survival for this salamander (USFWS 2002). The lack of a constant, clean water supply is another pressing issue. Eurycea tonkawae’s main water supply originates from the Edwards and Trinity Aquifers, which are located in areas highly susceptible to urbanization. Some of the aquifers near Jollyville Plateau are the sole sources of drinking water for nearby communities, further increasing the risk of a reduction in water flow to areas inhabited by Eurycea tonkawae (Herbez 2005). According to the Petition for E. tonkawae as an Endangered Species (2005), about 50% of northern watersheds were developed, with an additional 5% receiving approval for development. Currently, the Bull Creek watershed supports the largest populations of E. tonkawae, and has undergone major changes in development and urbanization in recent years. One tributary, Barrows Spring, has impervious cover of nearly 27%. However, several sewage spills occurred from 1993-1996, which may have resulted in high nitrate concentrations in Barrows Spring (Herbez 2005). Another tributary in Bull Creek, the Hanks tract, originally produced 70-80 salamanders during counts in 1997-1998. Currently, it is rare for more than one individual E. tonkawae salamander to be found there at any given time (City of Austin 2001). Heavy development and urbanizations around tracts and tributaries of Bull Creek suggest an uncertain future for Jollyville Plateau Salamanders in years ahead. E. tonkawae is sensitive to rapid development and urbanization that produces pollution as well as altering ion concentrations and reducing fresh water supply. Being restricted to a limited range makes the overall population highly susceptible to degradation of water quality. The future of E. tonkawae depends on constant water supply of adequate quality and in controlling the rate of urbanization around the major tracts and tributaries in which this species lives.

The Jollyville Plateau salamander (Eurycea tonkawae) is a species of salamander in the family Plethodontidae. It is also known as the Tonkawa Springs salamander. It is endemic to Travis and Williamson counties, Texas, United States. This species is perrenibranchiate, retaining its gills throughout life.

Eurycea tonkawae is the sister taxon to E. naufragia and E. chisholmensis, two other endemic perrenibranchiate central Texas salamanders.

Its natural habitats are freshwater springs, spring runs, and wet caves of the Buttercup karst system. Cave dwelling E. tonkawae may represent a distinct species, however further work is needed to clarify their taxonomic status.