Uncrewed Aerial Systems as tools for green turtle population assessment in coastal marine protected areas in Uruguay.

TERYDA N.; VELEZ RUBIO G.; PROSDOCIMI L.,; CARTHY, R.R.

Simposio; 42th Annual Symposium on Sea Turtle Biology and Conservation; 2024

ISTS

The green turtle (Chelonia mydas) is a highly migratory endangered species. Several direct threat-related strandings of turtles (i.e. bycatch and marine pollution) are reported yearly in the Southwestern Atlantic Ocean (SWAO), and consequently critical areas for sea turtle conservation have been identified in the region, including the coast of Uruguay. This region is an important foraging ground for juveniles feeding on macroalgae, which is a key component of rocky marine ecosystems and provides food and shelter to many species. To date, several efforts have been made to protect sea turtles and reduce threats, however, little attention has been given to evaluating habitat degradation at feeding grounds in SWAO, mainly due to cost and complex logistics. Long-term monitoring programs represent a valuable tool for decision-makers to prevent and mitigate possible threats to sea turtles, and due to their spatially complex life cycle and biology, research and conservation efforts for these animals have been relying on new technology and more efficient protocols to achieve a better understanding of population trends and threats. Recently, Uncrewed Aerial Systems (UAS, or drones) have been introduced for such studies. However, their implementation has been neglected in the SWAO, due in part to the limited sampling protocols available and low water visibility. This aims to develop a holistic approach to the conservation of juvenile green turtles by using UAS to conduct aerial surveys in Uruguayan feeding areas and to determine if this tool is viable to be implemented in long-term population studies. We used a UAS to survey juvenile green turtles in Cerro Verde e Islas de la Coronilla Coastal-Marine Protected Area (CMPA), Uruguay. We conducted aerial surveys over the water between December 2021-May 2022. We deployed the UAS from the shore, collecting video of the coastal foraging grounds while flying 200m linear transects at an altitude of 35 - 40 m. We conducted 123 missions in four survey areas over 25 field days. Mission duration depended on the survey area and flight times ranged from 7 to 16 minutes, totaling 20.4 hours of video. Days in the field were limited due to high wind and Beaufort Sea State, with operations only possible at mean wind speeds below 28kph (max gusts of 35kph) and sea state of 3. Depending on the survey area, we counted 0 – 70 turtle sightings with an outlier of 126 individuals. These results are preliminary with 30% of videos still being processed. The next step will be to calculate Observations-per-Unit-Effort and to estimate Relative Density of green turtle in CMPA accounting for individuals not available to being seen (Probability of being visible). This ongoing work demonstrates that UAS are effective tools for performing sea turtle monitoring in a region that was previously understudied due to environmental factors such as water clarity. Furthermore, we show the potential benefit of using UAS in sub-optimal environmental and oceanographic conditions, providing information and opportunities to study habitat use, distribution and density of the juvenile green turtle in the main feeding area in Uruguay.