Estimation of Jollyville Plateau Salamander (Eurycea tonkawae) populations using surface counts and mark-recapture

The Jollyville Plateau salamander (Eurycea tonkawae) is a perennibranchiate salamander found only in springs, spring runs, and subterranean streams in the Northern Edwards Aquifer northwest of Austin, Texas. This species is currently a candidate for listing under the Endangered Species Act due to threats from urban development throughout its limited range and corresponding negative trends in surface counts at several long-term monitoring sites. During 2007, the City of Austin initiated markrecapture surveys of E. tonkawae populations at three spring sites and has compared the results with surface count surveys, which have been conducted as part of a long-term monitoring program since 1997. The mark-recapture study was conducted monthly over an 8-month period using Pollock\u27s robust design. The original purpose of the mark-recapture surveys was to assess the potential impacts of a proposed water treatment plant (WTP4), which was subsequently relocated to an alternate site. While documenting the effects of WTP4 is no longer necessary, this study provided a unique opportunity to compare the utility of mark-recapture and surface counts. Mark-recapture surveys are considerably more labor-intensive, yet provide critical information that cannot be obtained solely from surface counts, including detection probabilities, total population size, vital rate estimates (emigration/immigration, persistence), and surface movement. During this study, detection probabilities varied from month-to-month, but the mean probabilities were similar across all three sites. These preliminary results indicate that, under ideal habitat conditions (i.e., consistent spring flow, suitable cover, and few predators), surface counts should represent a consistent fraction of the total population and thus provide a reliable index of the total population size. Continuing markrecapture at a subset of the monitoring sites is recommended to better understand how populations respond under less than ideal conditions, monitor variability in detection probabilities over a longer period of time, adjust surface count data as needed, and gather other data that cannot be obtained from surface counts. -- Authors Open Access - Permission by Publisher See Extended description for more information