Short Communication
Print
Short Communication
A modified trap design for sampling subterranean habitats for central Texas Eurycea salamanders
expand article infoRyan M. Jones, Zachary C. Adcock, Andrew R. MacLaren, Kemble White IV
‡ Cambrian Environmental, Austin, United States of America
Open Access

Abstract

In this paper, we describe modifications to a sampling technique for surface, stream-dwelling salamanders for use in subterranean settings. Leaf litter bags are an effective and commonly used trap for salamanders, and their construction purposefully allows animals to move freely in and out of the trap. However, this presents a problem in subterranean deployment because retrieving the trap over long vertical distances, such as well sampling, allows time and space for the animals to escape. To overcome this challenge, we enclosed a leaf litter bag in a suspended net system contained by a lanyard to sample a 3-meter deep well. Our trap modifications resulted in the live capture of adult and immature federally threatened Salado Salamanders (Eurycea chisholmensis) from the well in addition to aquatic invertebrates. This represents a novel trapping technique within a habitat system for which stygofauna sampling options are limited.

Keywords

Active trap, Amphibian sampling, Karst Biology, Leaf litter trap, Salado Salamander, Stygofauna, Threatened Species

Introduction

Knowledge of stygofauna and their ecology is inevitably less available than that of epigean fauna because the subterranean habitats stygofauna occupy are less accessible for sampling (Hahn 2002; Larned 2012; Hose et al. 2017). Conducting manual biological surveys (i.e., hand collection) may be a preferred way to collect stygofauna, but this requires a point of access to the subterranean environment in the form of geologic features such as caves or sinkholes. The occurrence of these geologic features is often rare (Larned 2012), especially features large enough to accommodate human passage.

Subterranean sampling and trapping techniques have been developed to survey areas inaccessible to humans. Commonly employed methods for sampling stygofauna have been restricted to the hyporheic zone using water well or bore sampling, as well as the deployment of traps (Larned 2012). Hyporheic zone sampling often involves the extraction of interstitial water through methods such as hyporheic pumping, which allows researchers to collect organisms residing in the water-sediment interface. For deeper groundwater environments, bottle traps or funnel traps are commonly employed. These are typically deployed in wells or at cave entrances to capture fauna inhabiting these otherwise inaccessible zones. While these methods primarily target invertebrates, such as crustaceans and other small aquatic organisms (Benedict 1896; Fenolio et al. 2015, 2017; Külköylüoğlu et al. 2017a, 2017b, 2017c), targeted sampling strategies are essential for vertebrates when they do occur in these environments.

Despite extensive research on invertebrate sampling, methods for effectively sampling subterranean vertebrates remain less established. Although the use of bottle and funnel traps to sample for stream-dwelling (i.e., epigean) salamanders is also well documented (e.g., Richter 1995; Mushet et al. 1997; Fronzuto and Verrell 2000; Wilson and Dorcas 2003; Nowakowski and Maerz 2009), their effectiveness for subterranean vertebrates is limited and not well documented (McDermid et al. 2015). Despite their utility, bottle traps and funnel traps have drawbacks. Because these traps restrain captured animals, they must be checked frequently to prevent mortality, a critical consideration when researching endangered and threatened species (Willson and Gibbons 2010).

A popular technique for sampling surface (i.e., epigean) stream-dwelling salamanders is the use of leaf litter bags (Pauley and Little 1998; Jung et al. 2000; Waldron et al. 2003; Edwards et al. 2016). Leaf litter bags attract and concentrate, rather than trap, fauna by providing favorable structure objects, and animals are able to freely move in and out of the bag (Willson and Gibbons). This makes leaf litter bags a favorable technique when deploying traps for long periods because there is less risk of accidental death from target fauna becoming truly trapped and not being able to leave the trap (Waldron et al. 2003). This is especially important for listed endangered or threatened species, where the health and well-being of the animals takes precedence.

In surface waters, researchers check leaf litter bags by quickly sliding a tray or sieve under the bag to catch any target fauna that may fall through the mesh netting (Willson and Gibbons 2010). However, this presents a problem in subterranean deployment because traps often need to be retrieved vertically through the water column (or air), allowing ample time for fauna to escape. Here, we present a technique to remedy this problem to allow the effective use of leaf litter bags in subterranean settings.

The study species

The target of this sampling methodology was Salado Salamanders (Eurycea chisholmensis), a fully aquatic groundwater obligate salamander. Salado Salamanders are the northernmost species within a radiation of central Texas Eurycea salamanders and are endemic to groundwater habitats north of the San Gabriel River and south of Salado Creek in Williamson and Bell counties, Texas. (US Fish and Wildlife Service 2014; Devitt et al. 2019). Because of anthropogenic pressures and concerns of reduced water quantity and quality within the Edwards/Trinity aquifer system that contains this radiation of distinct species, E. chisholmensis along with several other species in this radiation have been listed under the Federal Endangered Species Act or are being prepared for future proposed listings (e.g., U.S. Fish and Wildlife Service 2013, 2014).

Methods

Study area

Cobbs Spring is ephemeral and discharges from the northern segment of the Edwards Aquifer in the Berry Creek watershed and is located on private property within Williamson County, Texas, USA. The soil and associated geology near the spring consists of silty and clayey slope alluvium underlain by Edwards limestone. Pecan (Carya illinoinensis) is the dominant overstory vegetation surrounding the spring. Within the spring run, the Edwards limestone is weathered entirely exposing the topmost Comanche bedrock.

Early settlers of this property installed an approximately 3 m deep hand-dug well (Fig. 1) located about 100 m downstream of the spring outlet and 50 m west of the main channel of the spring run. We observe this well gaining and losing water in correspondence with discharge volume in the spring itself, and thus we assume it is fed by the same source of groundwater. We visited Cobbs Spring monthly as part of an ongoing capture-mark-recapture study of Eurycea salamanders at select Williamson County sites (Cambrian 2020, 2021). Salamanders are previously known to occur within the well (U.S. Fish and Wildlife Service 2014), and we opportunistically observed salamanders in the well over the course of population monitoring.

Figure 1. 

Hand cut limestone well under a pecan tree. The well near Cobbs Spring is a relatively shallow well made of limestone blocks that were cut by hand. Situated under a pecan tree, the well is uncovered, allowing leaves and organic matter to naturally fall inside.

Trap design

We modify a commonly used and documented trapping technique for stream-dwelling salamanders (Jung et al. 2000; Waldron et al. 2003; Edwards et al. 2016; Peirson et al. 2016) for use in subterranean aquatic applications. Although the factors influencing stygofauna occurrence are not well studied, some research indicates that the most important factors are habitat structure and the supply of organic matter (Korbel and Hose 2015; Ercoli et al. 2019). The method we describe herein adds a potential foraging environment to a sparse environment. This may attract salamanders either for its use as habitat structure or by first attracting salamander prey species with food in the form of organic leaf matter, which in turn attract salamanders.

Our goal when designing this trap method was to create a leaf litter bag that could be lowered into a well within a mesh bag (Figs 2, 3), which when lowered to the bottom of the well would lay flat allowing salamanders access to the leaf litter trap (Fig. 4), but upon extraction enclose around the leaf litter trap (Fig. 5), ensuring capture of all animals harbored within. Leaf litter bags are typically fashioned from polypropylene mesh netting designed for landscaping; leaf litter is collected and contained within the poly netting. Although the netting is typically used to exclude deer or birds, salamanders are able to enter and leave the ‘trap’ freely because the 2.5 cm wide squares that make the netting are large enough for several salamander species to pass through. We constructed a leaf litter bag approximately 30 cm × 30 cm × 45 cm in size using “Vigoro Polypropylene Deer Block Netting, UV Treated” (Model # NMVDB07100 Store SKU #295769 purchased from Home Depot) which has 1 inch (2.54 cm) apertures, and cable ties. The leaf litter used was collected at the site and composed mostly of Pecan, which also naturally occurs inside the well from the surrounding canopy. We used native leaf litter collected at the site because a change to the quality or quantity of litter entering caves has the potential to disrupt the structure and function of cave communities (Hillis et al. 2008). Additionally, Pecan leaves are larger than the 2.5 cm aperture of the deer block netting allowing them to be contained satisfactorily. The bottom of the trap was made from a “Leslie’s Pro grade 18 inch Leaf Rake” (Sku: 82627 LPM #: 82627; manufacturer location - HQ - Phoenix Arizona) brand pool skimmer. This device features a fine mesh whose apertures are smaller than we would expect any Eurycea salamander, at any life stage, to be able to escape through. The pool skimmer was deconstructed and only the mesh bag was used to fashion the trap. A wire coat hanger was modified into a circle and mounted onto the rim of the pool skimmer bag with cable ties. In order to lower the trap into the well, 30lb test monofilament line was tied to four areas on the rim of the wire coat hanger circle. With the leaf litter bag inside the pool skimmer bag, the trap was lowered to the bottom of the well, adjusting the position so that the pool skimmer bag laid flat along the bottom of the well.

Figure 2. 

Leaf litter bag and modified pool net. A leaf litter bag is held above a modified pool bag, demonstrating the trap used for collecting and examining aquatic salamanders.

Figure 3. 

Lowering the Leaf Litter Trap into the Well. The image shows the trap being lowered into the well using the lanyard. The leaf litter bag, contained within the pool net, is carefully guided down to the bottom of the well, positioning it to lay flat and become accessible to salamanders. This setup ensures a smooth descent and accurate placement of the trap in the well.

Figure 4. 

Leaf litter bag with no lanyard tension. Illustrating how the leaf litter bag is fully accessible to salamanders when the pool net lies flat against the bottom of the well, with no tension on the lanyard. This design ensures that the leaf litter bag provides unobstructed access to the trap contents, allowing salamanders to enter and leave freely.

Figure 5. 

Leaf litter bag with lanyard tension. Demonstrating the trap in its closed position with tension applied to the lanyard, causing the pool net to enclose the leaf litter bag. This configuration securely captures the salamanders and prevents their escape, ensuring all animals within are retained during extraction.

The trap was checked four hours after first deployment (Fig. 6), it was then redeployed and rechecked three times, each one month apart coinciding with our capture-mark-recapture study. We retrieved the trap by hoisting it out of the well by the 30lb test monofilament line. Each time the trap was checked, water from the nearby spring was collected and then poured over the leaf litter bag as it was gently shaken to allow any invertebrates and salamanders to fall out of the leaf litter bag and into the pool skimmer bag. While processing the invertebrates and salamanders that ended up in the pool skimmer bag, we placed the leaf litter bag over a sieve (Adcock et al. 2022) in case any more invertebrates or salamanders remained in the leaf litter bag after the initial washing and shaking. Salamanders were categorized as juvenile if their total length was approximately <25 mm based on a visual estimate (Pierce et al. 2010) and also checked for gravidity (i.e., the presence of oocytes within the translucent venter). Salamanders were then photographed against a 5 mm background to be later measured for total length and snout-trunk length (STL) and to identify individuals (Bolger et al. 2012; Bendik et al. 2013). Salamanders were then replaced into the pool skimmer bag along with the leaf litter trap and returned to the well, as the trap system was redeployed. Representative specimens of each captured invertebrate were also vouchered, and excess captures were released back into the well, following the same protocol as with the salamanders. Recaptured salamanders were identified from dorsal photos based on their unique chromatophore patterns using the free open-source photo recognition software ‘Wild ID’, a tool designed to identify individuals based on unique patterns from photos instead of using a physical tag on the animal (Bolger et al. 2012). Salamanders were measured from photos using the free open-source software ‘Image J’, using the 5 mm grid background as a reference.

Figure 6. 

First captured Eurycea chisholmensis with this trap. The first two federally listed E. chisholmensis salamanders captured using the modified leaf litter trap. One is an adult, and the other is a juvenile, showcasing the trap’s effectiveness in capturing different life stages. Photos of these salamanders were taken to be able to identify them as recaptured in successive surveys using the Wild ID software.

Results

A total of 18 salamanders were captured, representing 12 unique individuals (determined through capture mark recapture methods) (Table 1). Multiple salamanders were captured during every sampling event, and we never collected an injured or dead salamander (Table 2). We additionally captured four species of invertebrates representing three Classes (Insecta, Clitellata, and Gastropoda), as well as Rio Grande Leopard Frog tadpoles (Lithobates berlandieri).

Table 1.

Salado Salamander (Eurycea chisholmensis) measurement and gravidity data.

Date Salamander Unique ID Total Length (mm) STL (mm) Gravid
31 Oct 2019 C0432 24.1 14.6 No
C0433 47.1 25.9 No
20 Nov 2019 C0434 32.4 18.3 No
C0435 33.7 18.6 No
C0436 43.2 23.0 No
19 Dec 2019 C0432 24.9 15.8 No
C0454 43.6 25.7 No
C0435 33.6 19.3 No
27 Jan 2020 C0435 34.7 19.0 No
C0470 40.6 22.5 No
C0471 30.3 17.7 No
24 Feb 2020 C0493 32.6 19.2 No
C0494 31.5 20.0 No
C0495 34.0 21.0 No
C0470 41.2 23.9 No
C0471 31.6 20.4 No
C0496 42.2 24.5 No
C0432 28.4 17.7 No
Table 2.

Salado Salamander (Eurycea chisholmensis) capture results using the modified leaf litter trap.

Date Deployment Time Total Adult Captures Total Juvenile Captures Recaptured Individuals
31 Oct 2019 4 hours 1 1
20 Nov 2019 20 days 3 0 0
19 Dec 2019 29 days 2 1 2
27 Jan 2020 39 days 3 0 1
24 Feb 2020 28 days 7 0 3

Discussion

Stygofauna are understudied, and many species within this group are of conservation concern due to their cryptic nature (Hahn 2002; Simões et al. 2013). These species are often granted protected status, such as threatened or endangered, under the Endangered Species Act, necessitating research and data collection (Doremus and Pagel 2008). Consequently, there is a critical need to develop and refine survey techniques to provide reliable sampling options for practitioners working to conserve and manage these vulnerable species.

Although this water well is shallow and open to the surface, we expect the methods we describe above to be applicable to a variety of sampling requirements and unique situations. The successful capture of salamanders within this well, given its proximity to the known occupied spring, demonstrates the use of subterranean habitat by this species within the karst subterranean habitat that underlies the uplands.

The recapture of 6 unique individual salamanders over five sampling events without mortalities demonstrates that salamanders can enter and leave the trap safely. This trap was designed specifically for this well, but it could potentially be used as a sampling technique for other wells, caves, and hard-to-reach places in occupied springs. This methodology may also have utility to inventory invertebrates that utilize leaf litter, and in federally mandated occurrence surveys for this group of salamanders (USFWS 2021). With some modifications, we expect that this trap can be deployed in various deep-water settings, caves, solution cavities, and wells of different sizes and depths. Additionally, the leaf litter bag could be replaced by other artificial structures meant to attract fauna, such as mop heads, which are commonly used to sample both groundwater salamanders and invertebrates (e.g., Gibson et al. 2008; Devitt and Nissen 2018). There are additional species within the genus Eurycea that are federally listed and continue to be understudied, especially in subterranean habitats. This sampling method holds potential for effective use in studying the majority of this genus within the Edwards/Trinity aquifer system, given the shared life history strategies observed among most central Texas Eurycea species.

Acknowledgements

This work was supported by the Williamson County Conservation Foundation. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

References

  • Benedict JE (1896) Preliminary descriptions of a new genus and three new species of crustaceans from an artesian well at San Marcos, Texas. Proceedings of the United States National Museum 18(1087): 615–617. https://doi.org/10.5479/si.00963801.18-1087.615
  • Bendik NF, Morrison TA, Gluesenkamp AG, Sanders MS, O’Donnell LJ (2013) Computer-assisted photo identification outperforms visible implant elastomers in an endangered salamander, Eurycea tonkawae. PLOS ONE 8(3): e59424. https://doi.org/10.1371/journal.pone.0059424
  • Cambrian Environmental (2020) 2019 Annual Eurycea monitoring activities carried out under the Williamson County Regional Habitat Conservation Plan. Unpublished technical report prepared for the Williamson County Conservation Foundation, 46 pp.
  • Cambrian Environmental (2021) 2020 Annual Eurycea monitoring activities carried out under the Williamson County Regional Habitat Conservation Plan. Unpublished technical report prepared for the Williamson County Conservation Foundation, 44 pp.
  • Devitt T, Nissen BD (2018) New occurrence records for Eurycea sosorum Chippindale, Price & Hillis, 1993 (Caudata, Plethodontidae) in Travis and Hays counties, Texas, USA. Check List 14(2): 297–301. https://doi.org/10.15560/14.2.297
  • Devitt TJ, Wright AM, Cannatella DC, Hillis DM (2019) Species delimitation in endangered groundwater salamanders: implications for aquifer management and biodiversity conservation. Proceedings of the National Academy of Sciences 116(7): 2624–2633. https://doi.org/10.1073/pnas.1815014116
  • Edwards E, Pauley TK, Waldron JL (2016) Estimating spring salamander detection probability using multiple methods. Journal of Herpetology 50(1): 126–129. https://doi.org/10.1670/15-041
  • Ercoli F, Lefebvre F, Delangle M, Godé N, Caillon M, Raimond R, Souty‐Grosset C (2019) Differing trophic niches of three French stygobionts and their implications for conservation of endemic stygofauna. Aquatic Conservation: Marine and Freshwater Ecosystems 29(12): 2193–2203. https://doi.org/10.1002/aqc.3227
  • Fenolio DB, Niemiller ML, Mckee AM (2015) Conservation status of the Georgia Blind Salamander (Eurycea wallacei) from the Floridan Aquifer of Florida and Georgia. Reptiles & Amphibians 20(3): 97–111. https://doi.org/10.17161/randa.v20i3.13945
  • Fenolio DB, Niemiller ML, Gluesenkamp AG, McKee AM, Taylor SJ (2017) New distributional records of the stygobitic crayfish Cambarus crytodytes (Decapoda: Cambaridae) in the Floridan Aquifer system of southwestern Georgia. Southeastern Naturalist 16(2): 163–181. https://doi.org/10.1656/058.016.0205
  • Fronzuto J, Verrell P (2000) Sampling aquatic salamanders: tests of the efficiency of two funnel traps. Journal of Herpetology 34(1): 146–147. https://doi.org/10.2307/1565252
  • Hahn HJ (2002) Methods and Difficulties of Sampling Stygofauna—An Overview. In: Field Screening Europe 2001: Proceedings of the Second International Conference on Strategies and Techniques for the Investigation and Monitoring of Contaminated Sites. Dordrecht: Springer Netherlands, 201–205. https://doi.org/10.1007/978-94-010-0564-7_32
  • Hose GC, Fryirs KA, Bailey J, Ashby N, White T, Stumpp C (2017) Different depths, different fauna: habitat influences on the distribution of groundwater invertebrates. Hydrobiologia 797(1): 145–157. https://doi.org/10.1007/s10750-017-3166-7
  • Jung RE, Droege S, Sauer JR, Landy RB (2000) Evaluation of terrestrial and streamside salamander monitoring techniques at Shenandoah National Park. Environmental monitoring and assessment 63: 65–79. https://doi.org/10.1023/A:1006413603057
  • Korbel K, Hose GC (2015) Habitat, water quality, seasonality, or site? Identifying environmental correlates of the distribution of groundwater biota. Freshwater Science 34(1): 329–343. https://doi.org/10.1086/680038
  • Külköylüoğlu O, Akdermir D, Yavuzatmaca M, Schwartz BF, Hutchins BT (2017a) Rugosuscandona, a new genus of Candonidae (Crustacea: Ostracoda) from groundwater habitats in Texas, North America. Species Diversity 22(2): 175–185. https://doi.org/10.12782/specdiv.22.175
  • Külköylüoğlu O, Akdermir D, Yavuzatmaca M, Diaz PH, Gibson R (2017b) On Schornikovdona gen. nov. (Ostracoda, Candonidae) from rheocrene springs in Texas (U.S.A). Crustaceana 90(11–12): 1443–1461. https://doi.org/10.12782/specdiv.22.175
  • Külköylüoğlu O, Yavuzatmaca M, Akdemir D, Schwartz BF, Hutchins BT (2017c) Ufocandona hanneleeae gen. et. sp. nov. (Crustacea, Ostracoda) from an artesian well in Texas, USA. European Journal of Taxonomy 372: 1–18. https://doi.org/10.5852/ejt.2017.372
  • Nowakowski A, Maerz J (2009) Estimation of larval stream salamander densities in three proximate streams in the Georgia Piedmont. Journal of Herpetology 43(3): 503–509. https://doi.org/10.1670/07-128R2.1
  • Pierce BA, Christiansen JL, Ritzer AL, Jones TA (2010) Ecology of Georgetown salamanders (Eurycea naufragia) within the flow of a spring. The Southwestern Naturalist 55(2): 291–297. https://doi.org/10.1894/WL-30.1
  • Richter KO (1995) A simple aquatic funnel trap and its applications to wetland amphibian monitoring. Herpetological Review 26(2): 90–91.
  • Simões LB, Ferreira T, Bichuette ME (2013) Aquatic biota of different karst habitats in epigean and subterranean systems of Central Brazil – visibility versus relevance of taxa. Subterranean Biology 11: 55–74. https://doi.org/10.3897/subtbiol.11.5981
  • Willson JD, Gibbons JW (2010) Drift fences, coverboards, and other traps. In: Dodd Jr CK (Ed.) Amphibian Ecology and Conservation: A Handbook of Techniques. Oxford University Press Inc., New York, 229–245. https://doi.org/10.1093/oso/9780199541188.003.0013
  • US Fish and Wildlife Service (2013) Endangered and threatened wildlife and plants; determination of endangered species status for the Austin Blind salamander and threatened species status for the Jollyville Plateau salamander throughout their ranges; final rule. Federal Register 78: 51278–51326.
  • US Fish and Wildlife Service (2014) Endangered and threatened wildlife and plants; determination of threatened species status for the Georgetown salamander and Salado salamander throughout their ranges; final rule. Federal Register 79: 10235–10293.
login to comment