Utilizing Drones to Assess the Body Condition of Tamanend's Bottlenose Dolphins (Tursiops erebennus) in the Charleston Estuarine System.

Body condition is a measure of an animal's energy reserves relative to its body structure that provides important information about individual- and population-level health. Monitoring the body condition of free-ranging cetaceans has historically been difficult, but in recent years, the unmanned aerial system (UAS, or "drone") has facilitated noninvasive ways of estimating the cetacean body condition. The Charleston Estuarine System (CES) includes the estuarine and coastal ecosystems surrounding Charleston, South Carolina, and is utilized by Tamanend's bottlenose dolphins (Tursiops erebennus) throughout the year. The main goals of this study were (1) to test if UASs are suitable for monitoring body condition of dolphins in an estuarine environment, and (2) to determine if site, season, and age class influence the body condition of dolphins in the CES. Land-based UAS surveys were conducted at four sites throughout the CES between September 2022 and May 2023. The body condition of each dolphin was evaluated using images of the individual positioned flat with a straight body at the surface, and a linear mixed effects model was constructed to determine which effects were associated with significant differences in dolphin body condition. After filtering images for quality, 428 images of 174 unique dolphins were included in the final analysis, with repeated body condition estimates of 24 dolphins from multiple seasons. Both season and age class were significant predictors of dolphin body condition, but site was not. In addition, individual dolphins were catalogued in a Drone Dolphin ID database, which allowed some dolphins' unique body condition changes to be tracked over time. These findings provide an important baseline for dolphin body condition in the CES that can be built upon in future studies to better understand how body condition changes in response to environmental and anthropogenic stressors or for different age classes. [ABSTRACT FROM AUTHOR]