Unmanned 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

Simposio; 41th Annual Symposium on Sea Turtle Biology and Conservation; 2024

ISTS

The green turtle (Chelonia mydas) is a highly migratory endangered species. Several of 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 SWAO, including the coast of Uruguay. Moreover, this region is a key foraging ground for juveniles feeding macroalgae which is a key component of rocky marine ecosystems, providing food and shelter to many species. To date, several efforts have been made to protect sea turtles and reduce their threats, however, little attention has been given to evaluate habitat degradation at feeding grounds in SWAO mainly due to its cost and complex logistics. Nevertheless, long-term monitoring programs represent a valuable tool for decision-makers to prevent and mitigate possible threats to sea turtles. Further, 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 their population trends and threats. Recently, Unoccupied Aerial Systems (UAS, also known as drones) have been introduced for such studies. However, their implementation has been neglected for in the SWAO, due in part to the limited sampling protocols available and low water visibility. For this reason, the aim of the project was to develop and consolidate a holistic approach to the analysis and conservation of the green turtle and its coastal habitats. For the first phase we used a UAS to survey juvenile green turtle in Cerro Verde e Islas de la Coronilla Coastal-Marine Protected Area (CMPA), Uruguay.We used an UAS to conduct aerial surveys over the water during December 2021, January – May 2022. We deployed the UAS from the shore collecting video of the coastal foraging grounds while following specific flight it will consist of 200m linear transects connected in a zigzag pattern at an altitude of 35 - 40 m. We conducted a total of 123 missions throughout 4 survey areas over a total of 25 field days. Our mission duration depended on the survey area and flight times ranged 7 to 16 minutes, totaling 20.4 hours of video. Days in the field were limited due to high wind and Buford state, only being able to fly with mean wind speed below 28kph (max gusts of 35kph) and sea state of 3. Depending on survey area, we counted a range of 0 – 14 sightings for the lower count missions to 35 – 126 sightings on the higher count missions. It must be noted that these results are preliminary, and there are remaining videos still to be processed. Furthermore, the following step will be to analyze the data with the statistical software DISTANCE to obtain a relative abundance estimate of the juvenile green turtle in CMPA. Nonetheless, this first step showed UAS are effective tools for performing sea turtle monitoring in coastal areas in a region that had been neglected due to environmental factors such as water clarity.