A Comparison of Survey Methodologies for the Federally Threatened, Narrow Range Endemic Neuse River Waterdog (Necturus lewisi)

The Neuse River Waterdog (Necturus lewisi) is a large aquatic salamander endemic to the Neuse and Tar–Pamlico River basins of eastern North Carolina. It was federally listed as threatened in 2021 following observed declines in occurrence throughout its historical range. Identifying effective survey methodologies is crucial for monitoring population trends in response to threats and recovery actions. Current monitoring guidelines require conducting winter surveys with minnow traps, but N. lewisi have been commonly encountered in warmer months when performing snorkel surveys targeting other aquatic species. The objectives of this study were to compare the effectiveness of summer snorkeling and winter trapping (WT) as methods for detecting site presence of N. lewisi and to estimate the amount of effort required to assume absence. We hypothesized that detection of N. lewisi would be higher using the WT method than using the summer snorkeling method, and we tested this in a single-season occupancy framework, allowing us to account for imperfect detection and uncertainty in site occurrence. The top model estimated that average summer snorkeling and WT detection probabilities per visit were 0.43 ± 0.005 (SE) and 0.56 ± 0.03, respectively. We estimated that site absence could be assumed with 95% probability in approximately six summer snorkeling visits and approximately four WT visits. These estimates were driven by the weak positive effect of daily stream discharge on detection probability. Optimal survey conditions (i.e., high stream discharge) are most often experienced during winter months in the study area, and the seasonality in discharge appeared to cause the higher effectiveness of WT in this study. Due to the relative frequency of optimal conditions in winter months, WT should remain the standard survey method for N. lewisi. However, summer snorkeling was estimated to be as effective as WT when survey conditions were suboptimal (i.e., baseline discharge). Future studies should further clarify the impact of seasonal discharges on detection success and whether summer snorkeling could be a valuable secondary monitoring strategy. This analysis increased the knowledge of N. lewisi monitoring techniques and will help inform survey practices and management actions for this imperiled species.