A large-scale survey of the world's largest population of wild giant tortoises has found that the once-threatened species is thriving. The Aldabra giant tortoises live on the Aldabra atoll in Seychelles.
According to the latest survey led by the Seychelles Islands Foundation (SIF) and the University of Exeter, there are approximately 180,000 Aldabra giant tortoises on the atoll — the highest figure ever recorded for the species and far exceeding the human population of Seychelles.
The new number follows the research team's analysis of five years of tortoise count data, from 2018 to 2022. It is the first update since the widely cited figure of 100,000 individuals in the late 1990s.
Aldabra is one of only two places in the world where giant tortoises still live in the wild, alongside the much smaller Galápagos population.
Dr. Frauke Fleischer-Dogley, chief executive of SIF, said: "More than 180,000 giant tortoises roaming freely on our atoll is proof of what long-term conservation commitment can achieve. This is wonderful news for Seychelles, for the world and for everyone who has worked to protect Aldabra."
The study, published in the scientific journal Ecology and Evolution, shows the population was relatively stable over the period, with a best estimate of nearly 183,000 mature and sub-adult individuals.
In the 19th century, exploitation left fewer than 1,000 Aldabra tortoises on the atoll. Thanks to a recovery programme, the island became a strict nature reserve in 1981 and a UNESCO World Heritage Site in 1982. Researchers now consider it one of the Indian Ocean's greatest conservation successes, and the new study has confirmed that.
Dr. Nancy Bunbury, a co-author of the study, said: "The Aldabra giant tortoise monitoring programme is one of the longest-running in the region, but dense vegetation makes tortoises genuinely difficult to count in many places. By modelling both what we could see and what we could not, we have produced the most reliable baseline for Seychelles' iconic species, setting a benchmark for tracking the population over the coming decades."
Despite the good news, the study's authors warn that vigilance is still needed. Aldabra's climate is changing, with forecasts of longer and more frequent droughts expected to reduce shade and food for the tortoises, while rising sea levels threaten the atoll's low-lying areas. Invasive mammals remain a major threat, including feral cats and black rats that eat eggs and young tortoises.
According to the authors, removing the remaining invasive mammals could clear the last barrier to the population's growth and help it withstand future climate pressures.
Dr. Dave Hudson, a postdoctoral researcher at the University of Exeter's Cornwall campus, said: "This result is fantastic news for the tortoises and testament to the amazing work being done in the field. But it is important to remember that this number is a baseline — not an end point. I hope we have given conservation managers the evidence they need to track future changes and act early as tortoises face growing pressure from climate change, drought and invasive species."
