Towards Cost-Effective Coastal Monitoring: Evaluating UAV based Methods in Elasmobranch Nursery Assessment

Unmanned aerial vehicles (UAVs) have rapidly advanced wildlife monitoring by offering high-resolution data collection with minimal disturbance to target species. This study explores the use of a low-cost, commercially available UAV for marine research, focusing on the assessment of elasmobranch nursery habitats within a Maldivian mangrove lagoon system. The urgency of such monitoring is heightened by the widespread die-back of mangroves across the Maldives and their recent classification as Critically Endangered on the IUCN Red List of Ecosystems, emphasizing the need for rapid biodiversity assessments and effective ecosystem monitoring strategies. Elasmobranch nursery habitats are critical for the survival and replenishment of shark and ray populations, yet they remain poorly understood due to their remote and complex nature. While the broader ecological value of mangroves is widely recognized, their specific role in supporting elasmobranchs, through nursery functions, foraging, and refuge, remains understudied. With both mangroves and elasmobranchs increasingly threatened, advancing our understanding of this relationship is essential for improved monitoring strategies and ultimately efficient conservation. We compare two UAV-based survey methodologies, structured transects and timed overflights, assessing their efficacy in detecting and identifying juvenile sharks and rays. Key parameters such as altitude, speed, and survey duration were optimized to balance species visibility, technical constraints, and survey effort. All sightings were manually recorded through video analysis, and relevant technical and environmental factors were documented to inform protocol development. The preliminary findings reveal differences between methods, with high-altitude offering better spatial coverage, low-altitude higher identification confidence, and structured transects better estimates of abundance and density. Additionally, we have found insights into habitat use and behavior. This approach demonstrates the potential of accessible UAV technology for scalable, non-invasive monitoring of coastal shark and ray populations, with broader applications for marine conservation and habitat management in terms of development of standardized UAV based protocols for elasmobranch nursery assessment and long-term monitoring.