Predicting surface abundance of federally threatened Jollyville Plateau Salamanders (Eurycea tonkawae) to inform management activities at a highly modified urban spring

Abstract

Urban expansion has contributed to the loss of habitat for range restricted species across the globe. Managing wildlife populations within these urban settings presents the challenge of balancing human and wildlife needs. Jollyville Plateau Salamanders (Eurycea tonkawae) are a range restricted, federally threatened, species of neotenic brook salamander endemic to central Texas. Almost the entire geographic range of E. tonkawae is embedded in the Austin, Cedar Park, and Round Rock metropolitan areas of Travis and Williamson counties, Texas. Among E. tonkawae occupied sites, Brushy Creek Spring has experienced some of the most extensive anthropogenic disturbance. Today the site consists of small groundwater outlets that emerge in the seams within a concrete culvert underlying a highway. Salamanders persist within this system though they are rarely detected. Here, we model the occurrence of salamanders within the surface habitat of Brushy Creek Spring using generalized linear models. In the absence of available data regarding the amount of water that is discharged from the spring, we use accumulated rainfall as a proxy for discharge to estimate salamander abundance. Additionally, we present evidence of reproduction, recruitment, and subterranean movement by E. tonkawae throughout this site. Infrastructure maintenance is inevitable at Brushy Creek Spring. We intend for our results to inform when maintenance should occur, i.e., during environmental conditions when salamanders are less likely to be observed in the surface habitat, to avoid unnecessary impacts to this federally threatened species.

Development and validation of an environmental DNA assay to detect federally threatened groundwater salamanders in central Texas

“…We detected Septentriomolge eDNA at all field control sites including one site, Brushy Creek Spring, where we did not detect salamanders during the complementary visual encounter surveys ( Table 2 ). The surface habitat is highly modified at Brushy Creek Spring and visual encounter surveys without salamander detections are common [ 48 ]. Two samples from the spring outlet were positive for eDNA, indicating that we detected subterranean salamanders that were not available for detection by traditional visual encounter surveys.…”

“…of not detecting Septentriomolge DNA when Septentriomolge DNA is present). Septentriomolge-occupied sites had regular visual encounter surveys, and displayed a range of relative abundances, including sites that averaged few (e.g., 0-2) to many (e.g., > 60) salamander detections per survey [9,21,[47][48][49]. The distribution of salamanders at each field control site (i.e., the typical extent of the salamander population downstream of the spring outlet) was previously determined by visual encounter surveys [9,21,[47][48][49].…”

Balancing development and sustainability: Assessing risks and protecting aquatic biodiversity on US college and university campuses

“…The Jollyville Plateau salamander (JPS) is endemic to the Central Texas area and is listed as a G1 critical species in the NatureServe HUC‐8 species dataset (Bendik, 2017). The salamander's range is almost entirely encompassed within the Travis and Williamson County watersheds, where it inhabits the interstitial spaces between cover objects (e.g., rocks, leaf litter, plants) of spring‐fed streams and creeks, water‐filled caves, and small hillside seeps (Adcock et al, 2022). The salamander spends most of its life underground, retreating into the Edward's aquifer when streamflow declines.…”