Study estimates nearly 183,000 Aldabra giant tortoises

Aldabra Atoll is home to almost 183,000 adult and subadult giant tortoises, according to a new study that used statistical modelling to estimate animals missed by surveyors. The Seychelles Islands Foundation and the University of Exeter based the estimate on monitoring data gathered from 2018 to 2022. The figure exceeds the Seychelles’ human population, estimated at about 123,000 at the end of 2025. The study, published in Ecology and Evolution, represents the first update to a widely cited estimate of about 100,000 tortoises made in the late 1990s. Researchers caution that the newer figure does not show the population nearly doubling: earlier surveys did not fully account for tortoises hidden by vegetation or resting in shade. The researchers describe the tortoise population as relatively stable during the five-year study period. Their method estimated animals that could not be directly observed, addressing the difficulty of counting tortoises across the atoll’s varied terrain. Dense vegetation, including scrub and mangroves, can make the animals harder to detect. Aldabra, a remote atoll in the Indian Ocean, holds the largest known population of giant tortoises in the wild.