Evaluating Elasmobranch Nursery Habitats in the Maldives with Commercial UAVs: A Comparative Methodological Approach.

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 to improve monitoring strategies and effective conservation. The urgency of studying and monitoring these systems is emphasized by widespread mangrove die-back in the Maldives and their recent classification as Critically Endangered on the IUCN Red List of Ecosystems. This study investigates the presence, diversity, and spatial use of juvenile sharks and rays within a remote Maldivian mangrove lagoon using a low-cost, commercially available unmanned aerial vehicle (UAV). Two survey approaches, structured transects and timed overflights, were applied and compared. Key flight parameters (altitude, speed, duration) were optimized for species visibility, and sightings were manually extracted through video analysis. Preliminary findings indicate frequent sightings of juvenile individuals across several elasmobranch species, suggesting potential nursery function, though additional sampling over time would be necessary to formally define the site as a nursery area under established criteria. Spatial patterns observed during the surveys also offer preliminary insights into habitat use within the lagoon. This research also demonstrates the potential value of UAVs in advancing elasmobranch science as it enables non-invasive research of species diversity, habitat use, and behavior in sensitive, not easily accessible coastal ecosystems. The approach also supports the development of standardized UAV-based protocols for long-term monitoring and conservation of critical nursery habitats.