Survey finds about 180,000 giant tortoises on Seychelles' Aldabra Atoll, a record for the species

The count was led by the Seychelles Islands Foundation and the University of Exeter, whose team analysed five years of tortoise surveys carried out between 2018 and 2022. It is the first update since a widely cited estimate of 100,000 tortoises from the late 1990s. The findings were published in the scientific journal Ecology and Evolution.

The researchers put their best estimate at almost 183,000 adult and sub-adult tortoises and described the population as relatively stable across the survey period.

Aldabra Atoll is one of only two places in the world where giant tortoises are found in the wild. The other, the Galápagos, holds a much smaller population.

In the 19th century, exploitation of the animals left fewer than 1,000 Aldabra tortoises on the island. A recovery programme followed, and Aldabra became a strict nature reserve in 1981 and a Unesco site in 1982.

"More than 180,000 giant tortoises roaming freely on our atoll is proof of what long-term commitment to conservation can achieve," said Dr Frauke Fleischer-Dogley, chief executive of the Seychelles Islands Foundation. "This is wonderful news for Seychelles, for the world, and for everyone who has worked to protect Aldabra."

Dr Nancy Bunbury, a co-author of the study, said Aldabra's monitoring programme is one of the longest running in the region but that the atoll's dense vegetation makes counting tortoises genuinely difficult in places. "By modelling what we didn't see, as well as what we did, we've produced the most reliable baseline yet for this iconic Seychelles species, establishing a benchmark we can use to track the population for decades to come," she said.

The authors warn that continued vigilance is essential. Aldabra's climate is changing, with longer and more frequent droughts predicted to cut the shade and food available to the tortoises, while rising sea levels threaten low-lying parts of the atoll. Feral cats and black rats that prey on tortoise eggs and hatchlings remain a key threat. The authors say planned eradication of these invasive mammals could remove the last barriers to further growth and help the population withstand future climate pressures.

"These results are great news for the tortoises and testament to the fantastic work done in the field," said Dr Dave Hudson, a postdoctoral research associate at the University of Exeter's Cornwall campus. "But it's important to remember that the numbers provide a baseline – not an endpoint." He said the evidence should allow conservation managers to track future change and act early as the tortoises face increasing pressure from climate change, drought and invasive species.