Spatial Variation in Abundance Parameters of a Federally Threatened Groundwater Salamander Within and Among Central Texas Headwater Creeks

Abstract

ABSTRACT

Semi‐arid conditions in central Texas relegate Eurycea salamanders to aquatic habitats influenced by groundwater (i.e., springs, spring‐fed creeks, and subterranean water in alluvium and aquifers). Many studies have noted that epigean (surface) populations of central Texas Eurycea occur near spring outlets. Consequently, the U.S. Fish and Wildlife Service designated surface critical habitat units for three species as a uniform distance up and downstream of occupied spring outlets. Here, we used data from visual encounter and quadrat surveys to model relative abundance and relative density, respectively, of federally threatened Jollyville Plateau Salamanders (E. tonkawae) in relation to downstream distance from a spring outlet in headwater creeks. We additionally use recapture data to investigate movement within these systems and in relation to the critical habitat units. Consistent with other studies, E. tonkawae relative abundance and relative density decreased with increasing distance from a spring outlet, and E. tonkawae occurred outside of its federally designated surface critical habitat unit at some sites. Importantly, the downstream extent of E. tonkawae and the rate of change in relative abundance and relative density varied among sites, which is incongruent with the uniform federal surface critical habitat distance. We observed limited movement within the headwater creeks, with most salamanders recaptured within 5 m of their previous capture location.