Aldabra Atoll uses UAV surveys to inform marine megafauna monitoring and conservation planning |12 August 2025

Aldabra Atoll uses UAV surveys to inform marine

megafauna monitoring and conservation planning

New findings from Aldabra Atoll, one of Seychelles’ two Unesco World Heritage Sites, provide the first dedicated assessment of marine megafauna using uncrewed aerial vehicles (UAVs).

The study, part of the PhD research of Dr Cheryl Sanchez, establishes a baseline for conservation planning by identifying marine megafauna hotspots in Aldabra’s lagoon. It was conducted in collaboration with the Seychelles Islands Foundation (SIF) and the University of Pisa. By surveying 49 grid squares in the atoll’s western lagoon, Dr Sanchez recorded the distribution and density of key species, including turtles, sharks, rays, and dugongs, across a range of shallow marine habitats.

The research, published in Marine Biology in June 2025, shows how environmental factors, such as land proximity, tide height, time of day, and habitat type, influence species presence. These insights are especially valuable amid global climate change and biodiversity loss, and will inform long-term monitoring and management of this ecologically significant site.

Key findings:

The study revealed clear patterns in megafauna abundance and spatial distribution, shaped by both physical and environmental factors:

• Turtles were the most numerous, with an average density of 140.8 individuals/km², followed by sharks, rays, and dugongs.

• Species were not evenly distributed, with notable clustering of turtles, sharks, and rays in particular areas.

• Presence of land in a grid square emerged as the most consistent predictor of species density across all groups.

• Tide height, time of day, and habitat type also influenced distribution, particularly for rays.

• Turtle and ray counts increased with higher tide, while shark numbers remained relatively constant.

• Juvenile turtles were concentrated near Ile Moustique and Ile Esprit, indicating potential nursery areas.

• UAV surveys proved highly effective, allowing precise, non-invasive monitoring in remote, shallow-water environments.

According to Dr Nancy Bunbury, co-author and consulting director of research and conservation at SIF, “this is a particularly exciting study for Aldabra as it provides the first aerial survey of multiple species of marine megafauna in the lagoon and confirms drones as a promising tool for further surveys at Aldabra.”

As climate change and biodiversity loss intensify, these findings offer a critical reference for protecting marine megafauna in isolated and vulnerable ecosystems.

By integrating UAV technology with environmental modelling, the research demonstrates a scalable approach to monitoring species distribution that can inform evidence-based conservation in challenging field conditions.

Dr Frauke Fleischer-Dogley, chief executive of SIF, highlights that “especially considering the immense costs to operate and manage Aldabra Atoll due to its remoteness, SIF must investigate how the use of technology can facilitate monitoring and research”.

To strengthen future monitoring and improve the accuracy of abundance estimates, the study outlines several methodological and research recommendations:

• Conduct surveys year-round and across different lagoon areas to capture seasonal and spatial variations.

• Use species-level identification tools like low-altitude UAVs and stereo-video cameras to improve ecological insights.

• Validate size estimation methods with known-length objects to enhance measurement accuracy.

• Repeat surveys in selected grid squares to reduce double-counting and better track changes in abundance.

• Integrate tidal data and compare protected versus non-protected zones to understand natural and conservation-driven impacts.

Establishing reliable ecological baselines is key to protecting marine life under increasing pressure from habitat degradation and environmental change. This study highlights how innovative aerial survey techniques can support adaptive management and long-term conservation at Aldabra, one of the world’s most intact and biodiverse marine environments.

To view the full study, readers can request access from the authors or consult their institutional library’s journal subscriptions.

Full reference:

Sanchez, C.L., Bunbury, N., A’Bear, L. et al. Marine megafauna distribution and abundance at Aldabra Atoll via UAV survey. Mar Biol 172, 142 (2025).

https://doi.org/10.1007/s00227-025-04686-5

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