San Marcos Salamander
Covered Species Information
Authored by Connor Helsel
The San Marcos salamander (Eurycea nana) inhabits an acute geographic range in Spring Lake, San Marcos, Hays County and a short distance within the San Marcos River downstream from the Spring Lake dam spillway (U.S. Fish and Wildlife Service [USFWS], 1996). The Edwards Aquifer Habitat Conservation Plan (EAHCP) has implemented Conservation Measures to support this threatened species.
Reduced springflow is the greatest threat to the survival of the species. As high water velocity prevents the buildup of silt on the substrate, providing San Marcos salamanders with critical silt-free gravel habitat (Nelson, 1993). Accordingly, the EAHCP has established programs to protect springflow in times of drought, such as the Aquifer Storage and Recovery program and the Voluntary Irrigation Suspension Program Option.
San Marcos salamander
Endangered Species Act status
Reaches a size of <56 mm total length (<2.2 inches; Nelson, 1993).
Physical description and Life History
The San Marcos salamander is a member of the Plethodontidae family (lungless salamanders), endemic to central Texas (Chippindale et al., 2000). These salamanders are light brown in color with a row of mid-lateral pale spots dotting each side. The head is narrow, in proportion with the body, with colored external-gills and eyes are partly or wholly surrounded by a dark ring (Bishop, 1941).
This species of salamander is neotenic, meaning they retain traits from early life stages, such as gills and tail fins, throughout their entire life cycle (Bishop, 1941; Nelson, 1993). Captive populations of San Marcos salamander have been documented to live to at least 4 years of age (Campbell & Anderson, 2018; Chippindale & Fries, 2005).
San Marcos salamander courtship routines are intricate, with sequential steps lasting several minutes to an hour in captive reproductive encounters. A reliable captive breeding method has not been established and research is ongoing (Campbell & Anderson, 2018).
Sex is often determined through candling, a method in which light is shown though the salamander’s translucent skin to reveal gender identifiers (Campbell & Crow, 2017; Gillette & Peterson 2001). Gravid (egg carrying) females of this species have been found to lay clutches of fertilized eggs with hatching times between 16 and 24 days, according to one study by Najvar et al. (2007). In captivity, egg clutches are attached to aquatic vegetation and rocks. It is believed that egg clutches are attached to the underside of rocks around spring vents in the wild (Chippindale & Fries, 2005; Nelson, 1993).
Interestingly, the San Marcos salamander can detect chemical cues in the water that alert them to the presence of a predator, such as a largemouth bass (Epp & Gabor, 2008).
The San Marcos salamander can be found in Spring Lake and in the upper reaches of the San Marcos River, downstream of the Spring Lake dam (Nelson, 1993; USFWS, 1996).
Habitat and Diet
San Marcos Salamanders are completely aquatic and live in flowing springwater that maintains a temperature range of range of 21-22ºC (Chippindale & Fries, 2005; USFWS, 1996). The species inhabits silt-free gravel, cobble, and rock substrates typically found in areas of high springflow (Nelson, 1993).
These salamanders are often found amid aquatic vegetation, such as filamentous algae, Amblystegium, Cambomba, and Sagittaria (Diaz et al., 2015). This vegetation, along with the salamanders’ rocky habitat, supports food sources and provides protection from predators (Campbell & Crow, 2017; Diaz et al., 2015; USFWS, 1996).
The San Marcos salamander feeds primarily on invertebrates, especially chironomids and amphipods (Chippindale & Fries, 2005).
Bishop, S., C. (1941). Notes on Salamanders with Descriptions of Several New Forms. Occasional Papers of the Museum of Zoology, 451, 1–25.
Campbell, L., & Anderson, K. (2018). 2018 Salamander Reproduction Research Report: Investigating San Marcos Salamander Reproduction in Captivity. https://www.edwardsaquifer.org/wp-content/uploads/2020/04/2018-Refugia-Appendices.pdf
Campbell, L., & Crow, J. (2017). Captive Propagation Eurycea sp. 41. https://www.edwardsaquifer.org/wp-content/uploads/2020/04/2017-Refugia-Appendices.pdf
Chippindale, P. T., & Fries, J. N. (2005). Eurycea nana San Marcos Salamander. In M. J. Lannoo, Amphibian Declines: The Conservation Status of United States Species (pp. 755–756). University of California Press.
Chippindale, P. T., Price, A. H., Wiens, J. J., & Hillis, D. M. (2000). Phylogenetic Relationships and Systematic Revision of Central Texas Hemidactyliine Plethodontid Salamanders. Herpetological Monographs, 14, 1. https://doi.org/10.2307/1467045
Diaz, P. H., Fries, J. N., Bonner, T. H., Alexander, M. L., & Nowlin, W. H. (2015). Mesohabitat associations of the threatened San Marcos salamander (Eurycea nana) across its geographic range. Aquatic Conservation: Marine and Freshwater Ecosystems, 25(3), 307–321. https://doi.org/10.1002/aqc.2559
Epp, K. J., & Gabor, C. R. (2008). Innate and Learned Predator Recognition Mediated by Chemical Signals in Eurycea nana. Ethology, 114(6), 607–615. https://doi.org/10.1111/j.1439-0310.2008.01494.x
Gillette, J. R., & Peterson, M. G. (2001). The benefits of transparency: candling as a simple method for determining sex in red-backed salamanders (Plethodon cinereus). Herpetological Review, 32(4), 233.
Najvar, P. A., Fries, J. N., & Baccus, J. T. (2007). Fecundity of San Marcos Salamanders in Captivity… The Southwestern Naturalist, 52(1), 145–147. https://doi.org/10.1894/0038-4909(2007)52[145:FOSMSI]2.0.CO;2
National Academies of Sciences, Engineering, and Medicine. 2018. Review of the Edwards Aquifer Habitat Conservation Plan: Report 3. Washington, DC: The National Academies Press. https://doi.org/10.17226/25200
Nelson, J., M. (1993). Population Size, Distribution, and Life History of Eurycea nana in the San Marcos River [Southwest Texas State University]. https://www.edwardsaquifer.org/wp-content/uploads/2019/02/1993_Nelson_Eurycea-nana.pdf
U.S. Fish and Wildlife Service. 1996. San Marcos/Comal (Revised) Recovery Plan. Albuquerque, New Mexico. pp. x + 93 with 28 pages of appendices