Aldabra: nearly 180,000 giant tortoises, a record partly explained by the method
This is good news for anyone who loves reptiles. According to a study published on 4 September 2026 in Ecology and Evolution, roughly 180,000 giant tortoises live on Aldabra atoll in the Seychelles. The best estimate is almost 183,000 adults and subadults, a figure never reached in earlier counts.
What moves me is the contrast with the past. In the nineteenth century, hunting and exploitation had reduced the population on the atoll to fewer than 1,000 animals. Aldabra became a strict nature reserve in 1981 and a UNESCO World Heritage Site in 1982, and researchers regard it as one of the great conservation success stories of the Indian Ocean. The stability seen between 2018 and 2021 is thought to reflect that protection and the eradication of invasive species.
But the most interesting part, to my mind, is the method. The team, working with the Seychelles Islands Foundation and the University of Exeter, used a hierarchical Bayesian model that also estimates how many tortoises are hidden by dense vegetation, rather than simply adding up the ones that are visible. The authors warn that this figure should not be compared with the 100,000 tortoises counted in 1999 to conclude that the population has doubled. The difference comes largely from a method that picks up animals that previously went unseen.
Only two places in the world still have wild giant tortoises, Aldabra and the Galápagos, and Aldabra has the largest free-roaming population. For anyone interested in land tortoises, it is a reminder that protecting a habitat over the long term can really pay off.
Source: Sciencepost
What moves me is the contrast with the past. In the nineteenth century, hunting and exploitation had reduced the population on the atoll to fewer than 1,000 animals. Aldabra became a strict nature reserve in 1981 and a UNESCO World Heritage Site in 1982, and researchers regard it as one of the great conservation success stories of the Indian Ocean. The stability seen between 2018 and 2021 is thought to reflect that protection and the eradication of invasive species.
But the most interesting part, to my mind, is the method. The team, working with the Seychelles Islands Foundation and the University of Exeter, used a hierarchical Bayesian model that also estimates how many tortoises are hidden by dense vegetation, rather than simply adding up the ones that are visible. The authors warn that this figure should not be compared with the 100,000 tortoises counted in 1999 to conclude that the population has doubled. The difference comes largely from a method that picks up animals that previously went unseen.
Only two places in the world still have wild giant tortoises, Aldabra and the Galápagos, and Aldabra has the largest free-roaming population. For anyone interested in land tortoises, it is a reminder that protecting a habitat over the long term can really pay off.
Source: Sciencepost
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