Despite recognition that nearly one-third of the 6300 amphibian species are threatened with extinction, our understanding of the general ecology and population status of many amphibians is relatively poor. A widely-used method for monitoring amphibians involves injecting captured individuals with unique combinations of colored visible implant elastomer (VIE). We compared VIE identification to a less-invasive method – computer-assisted photographic identification (photoID) – in endangered Jollyville Plateau salamanders (Eurycea tonkawae), a species with a known range limited to eight stream drainages in central Texas. We based photoID on the unique pigmentation patterns on the dorsal head region of 1215 individual salamanders using identification software Wild-ID. We compared the performance of photoID methods to VIEs using both ‘high-quality’ and ‘low-quality’ images, which were taken using two different camera types and technologies. For high-quality images, the photoID method had a false rejection rate of 0.76% compared to 1.90% for VIEs. Using a comparable dataset of lower-quality images, the false rejection rate was much higher (15.9%). Photo matching scores were negatively correlated with time between captures, suggesting that evolving natural marks could increase misidentification rates in longer term capture-recapture studies. Our study demonstrates the utility of large-scale capture-recapture using photo identification methods for Eurycea and other species with stable natural marks that can be reliably photographed.

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Insights into the ecology and natural history of the neotenic salamander, Eurycea tonkawae, are provided from eight years of capture‐recapture data from 10,041 captures of 7,315 individuals at 16 sites. Eurycea tonkawae exhibits seasonal reproduction, with peak gravidity occurring in the fall and winter. Size frequency data indicated recruitment occurred in the spring and summer. Open‐population capture‐recapture models revealed a similar seasonal pattern at two of three sites, while recruitment was dependent on flow at the third site. Females can reach sexual maturity within one year, and oviposition likely takes place below ground. The asymptotic body length of 1,290 individuals was estimated as 31.73 mm (at ca. two years of age), although there was substantial heterogeneity among growth trajectories. Longevity was approximately eight years, and the median age for a recaptured adult was 2.3 years. Abundance estimated from closed‐population and robust‐design capture‐recapture models varied widely within and among sites (range 41–834), although, surprisingly, dramatic changes in abundance were not observed following prolonged dry periods. Seasonal migration patterns of second‐year and older adults may help explain lower ratios of large individuals and higher temporary emigration during the latter half of the year, but further study is required. Low numbers of captures and recaptures precluded the use of open‐population models to estimate demographic parameters at several sites; therefore, closed‐population (or robust‐design) methods are generally recommended. Based on observations of their life history and population demographics, E. tonkawae seems well adapted to conditions where spring flow is variable and surface habitat periodically goes dry.

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Shrinkage in body length, followed by growth, has rarely been documented in vertebrates and has been associated with stressful energetic and environmental conditions. Here, we document reversible shrinkage in an amphibian for the first time. Jollyville Plateau salamanders Eurycea tonkawae are neotenic (attain maturity while retaining an aquatic larval form) and inhabit springs and caves of a dissected aquifer in Travis County, TX, USA. We conducted mark‐recapture surveys on a spring‐dwelling population before and after an exceptional drought in 2008. Use of unique marks and digital photographs of individuals provided precise information on salamander growth rates during and after a period in which salamanders retreated to underground refugia to avoid desiccation during the drought. Tail width decreased significantly during the drought indicating a reduction in energy stores, a consequence of stressful environmental conditions. Unexpectedly, body length shrinkage also occurred during the drought and was followed by positive growth when spring flow resumed. Body length shrinkage could be an adaptation to coping with long periods of low food availability although its long‐term effects are unknown. Given the influence of body size on many ecological and physiological characteristics of organisms, plasticity in body size may have important consequences that go undetected by researchers if shrinkage is ignored.