Taking stock of nature:  Assomption’s biodiversity baseline assessment |20 July 2026

Between December 2025 and May 2026, the Seychelles Islands Foundation (SIF) commissioned a series of independent biodiversity assessments on Assomption Island to establish scientific baselines across its terrestrial and marine ecosystems. The findings will guide future conservation management, biosecurity planning, and long-term ecological monitoring, particularly in light of the ongoing hotel development.

SIF has been formally entrusted with overseeing biodiversity conservation and biosecurity on Assomption as part of its broader mandate to safeguard the ecological integrity of Aldabra. The assessments therefore examined a wide range of biodiversity components, including Aldabra giant tortoises, landbirds, ants, butterflies, marine turtles, invasive alien plants, and the island's coastal and shallow marine habitats.

A range of internationally recognised survey techniques was employed to establish these baseline datasets. The Aldabra giant tortoise populations was estimated using line transect distance sampling and encounter surveys, while landbirds were surveyed through point counts. Ant diversity was documented through more than 200 hours of active hand collection, and butterfly communities were assessed through over 30 hours of Pollard walks conducted across the island. A comprehensive drone survey, capturing more than 39,000 high-resolution aerial images, mapped the distribution of invasive alien plants.

Marine assessments were equally extensive. Historical records spanning more than 125 years of green turtle and hawksbill nesting, combined with on-foot beach surveys, provided valuable information on nesting habitats, nesting distribution, and long-term population trends. Beneath the ocean's surface, approximately 53 hectares of seabed were mapped, while underwater visual census surveys were undertaken along 50m transects to assess reef fish and macroinvertebrate communities. Water quality parameters, including temperature, salinity, pH, and dissolved oxygen, were also recorded using specialised monitoring equipment.

Together, these assessments provide the first comprehensive scientific baseline for Assomption's biodiversity and represent a significant milestone in understanding the island's natural heritage. The findings will inform SIF's recommendations for future development and management, ensuring that decisions are guided by robust scientific evidence and the precautionary principle. They also highlight the island's remarkable ecological value and reinforce the importance of protecting its unique biodiversity for future generations.

Seychelles Islands Foundation (SIF)