Abstract
Diamondback terrapins (Malaclemys terrapin) are challenging to monitor in their salt marsh habitat. However, large-scale monitoring is needed to understand the status of populations and effectively apply targeted management. The Georgia Department of Natural Resources (GA DNR) is interested in developing a long-term monitoring program that it can use for tracking relative levels of terrapin abundance among creeks throughout the state to trigger varying intensities of management actions. The objective of this study was to investigate the potential of repeated head counts and binomial N-mixture models to inform the GA DNR’s state-wide monitoring and management objectives. We used the unmarked repeated count method to categorize sites into 3 levels of relative abundance while accounting for uncertainty in estimates. However, relative abundance estimates were sensitive to the timing of sampling within the active season and location of sampling along the creek, indicating limitations of this method. Results also showed that as survey effort increased, the number of sites that could be confidently assigned to higher abundance categories also increased. Therefore, if an objective is to minimize the number of creeks requiring more intensive and potentially more restrictive management actions, a high level of survey effort is recommended. Because relative abundance estimates using head count methods varied with timing and location of sampling, survey methods would need to be standardized and consistent across years. If applied judiciously, a method using head count surveys and N-mixture models may be the most effective means of state- or region-wide monitoring of terrapins across large numbers of sites. Additionally, if integrated with ongoing, long-term capture–recapture studies at a smaller number of sites, the capacity for head count surveys to inform terrapin management decisions across large areas and many sites could be enhanced.
