This species is a member of the Typhlomolge clade of central Texas Eurycea (Hillis et al. 2001).

Listed as Critically Endangered because its extent of occurrence (EOO) is 60 km², it is considered to occur in one threat-defined location, and there is continuing decline in the extent and quality of its habitat in San Marcos Pool.

This species can be found in San Marcos Pool of the Edwards Aquifer, Hays County, south-central Texas, USA at an elevation of approximately 188 m asl (Chippindale et al. 2000, Green et al. 2014). It is unlikely to range beyond this region. Its extent of occurrence (EOO) is 60 km².

The total adult population size is unknown. Individuals of this species still appear common in outflows of Diversion Spring, a pipe that carries outflows from the Edwards Aquifer at San Marcos Springs. However, numbers collected vary widely from year to year and most individuals recovered are juveniles (Chippindale 2005). Local extirpations have occurred throughout this species' range (Green et al. 2014). Given these local losses and the ongoing decline in the quality and extent of this species' habitat, a decreasing population trend is suspected.

This species is known to inhabit subterranean caves and various types of wells (including artesian, hand-dug, and bored) (A. Gluesenkamp pers. comm. July 2021). Individuals have been observed climbing rock surfaces or swimming in open water. This species is completely aquatic and does not metamorphose. Breeding habits are unknown in nature; however, this species has bred on several occasions in captivity, including at the Dallas Aquarium at Fair Park, Cincinnati Zoo, Aquarena Centre (San Marcos), and San Marcos National Fish Hatchery and Technology Centre (L. Ables pers. comm. 2003) as well as the San Antonio Zoo, Audubon Zoo, National Aquarium (A. Gluesenkamp pers. comm. July 2021).

This species is sensitive to changes in water quality and thus vulnerable to groundwater pollutants (Matthews and Moseley 1990). It is also threatened by falling groundwater levels that have resulted from increased pumping to support rapidly expanding residential and commercial development in the region. The U.S. Census Bureau (2020) ranked several of the counties in the recharge and contributing zones of San Marcos springs as some of the fastest growing counties in the United States from April 2010–July 2019. Hays County, which holds the entire known range of this species, was ranked as the second fastest growing county with a population increase of 46.5%. Since 2000, Hays County has doubled in population size and experienced substantial associated growth in commercial, industrial, and residential development. This pace of growth is expected to continue over the next three decades (USFWS 2021). Over collecting in the past (1960s) might have reduced subpopulations in accessible locations, although this is no longer thought to be a threat due to the protected status of the species.

Climate change also poses a threat to this species. As temperatures increase and droughts increase in frequency and severity, the ongoing issue of groundwater depletion will be exacerbated further (T. Devitt, N. Bendik, and D. Hillis pers. comm. June 2021). Additionally, the emergence of the salamander chytrid fungus (Batrachochytrium salamandrivorans, “Bsal”) as an amphibian pathogen has caused dramatic declines in European fire salamanders since its apparent arrival in 2008 through the international pet trade (Feldmeier et al. 2016). Carter et al. (2020) found that Eurycea wilderae and E. lonicauda were susceptible to Bsal, and in lab tests altered their behavior upon infection and developed clinical chytridiomycosis. A separate study found that E. sosorum was a suitable host for Bsal, but upon infection did not alter behaviour or experience mortality (M. Gray unpub. data 2021). The response of this species is not known, but the genus does appear to be susceptible to infection. Sampling work conducted by Gluesenkamp et al. (2018) indicates that Bsal has not yet established in any native populations of E. rathbuni. Although the presence of the fungus has not been confirmed in the Americas, it is spreading in Europe and risks spreading further. Should Bsal be introduced to the US, the impacts on salamander populations could be rapid and severe if immediate mitigation action is not taken.

While this species was previously collected (1960s) for the pet trade, collection is now prohibited and is no longer thought to be a major threat. However, this decline in use is largely the result of site inaccessibility rather than a decline in interest. This is emphasized by the numerous illegal traps that were found and removed from Rattlesnake Cave before it was gated (Krejca and Gluesenkamp 2007).

Conservation Actions In-Place
The San Marcos River System is protected, and this species is listed as Endangered at both the state and federal level (Amphibiaweb 2021). Captive breeding programmes have been established and captive populations are currently held at the Audubon Zoo in Louisiana, the Detroit Zoological Zoo in Michigan, the Sedgewick County Zoo in Kansas, the Milwaukee Zoo in Wisconsin, and in three zoos in Texas: the Dallas Zoo, the Houston Zoological Gardens, and the San Antonio Zoological Gardens (USFWS 2021).

In an effort to prevent the introduction of Bsal into the US, an Interim Rule of the Lacey Act has been enacted that bans the importation of 201 species of salamanders (USFWS 2016). Additionally, a temporary voluntary trade moratorium of imports of Asian salamander species that are known to carry the disease until such time as effective testing and treatment regimens can be developed and distributed has been recommended to all exporters, shippers, sellers and buyers by the Pet Industry Joint Advisory Council (PIJAC). A North America Bsal Task Force has also been created, with working groups designed to address a variety of disease prevention and mitigation goals (North America Bsal Task Force 2021).

Conservation Needed
This species would likely benefit from improved habitat protection and management at sites where it is known to occur. Legislation and enforcement of legislation aimed at improving water quality are needed, as are improved water conservation efforts and campaigns.

Research Needed
More information is needed on this species' distribution, population status, ecology, and threats. There is a need for monitoring the population status and habitat of this species given the ongoing threats and declines.