Giant Tortoise Population Thrives, With 180,000 Discovered on Single Island

A comprehensive survey of Aldabra Atoll in the Seychelles has revealed a thriving population of Aldabra giant tortoises, with approximately 180,000 individuals now inhabiting the island. This figure represents the highest number ever recorded for the species and significantly surpasses the human population of the Seychelles.

The findings, published in the scientific journal Ecology and Evolution, are the result of a five-year analysis of tortoise counts conducted between 2018 and 2022 by the Seychelles Islands Foundation (SIF) and the University of Exeter. This marks the first update since a widely cited estimate of 100,000 tortoises from the late 1990s.

Aldabra Atoll is one of only two locations globally where giant tortoises can be found in the wild, with a smaller population residing in the Galapagos.

Dr. Frauke Fleischer-Dogley, CEO of SIF, stated, “More than 180,000 giant tortoises roaming freely on our atoll is proof of what long-term commitment to conservation can achieve.”

The study determined a population estimate of nearly 183,000 adult and sub-adult tortoises, indicating a stable population over the survey period. This recovery is a significant turnaround from the 19th century, when exploitation led to fewer than 1,000 Aldabra tortoises remaining on the island. Conservation efforts, including the establishment of the island as a strict nature reserve in 1981 and a UNESCO World Heritage site in 1982, have been credited with this resurgence.

Researchers now consider Aldabra's giant tortoise population one of the greatest conservation success stories in the Indian Ocean.

However, the study's authors caution that continued vigilance is necessary. Climate change poses a growing threat, with projections of longer and more frequent droughts expected to reduce available shade and food, while rising sea levels threaten low-lying areas of the atoll. Invasive mammals, such as feral cats and black rats, also continue to prey on tortoise eggs and hatchlings.

Dr. Nancy Bunbury, a co-author of the study, noted the challenges of conducting counts in Aldabra's dense vegetation. "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 suggest that eradicating remaining invasive mammals could remove the final obstacles to further population growth and enhance the tortoises' resilience to future climate pressures. Dr. Dave Hudson, a postdoctoral research associate at the University of Exeter, added, “Hopefully we have provided the conservation managers the evidence they need to track future change and act early as the tortoises face increasing pressures from climate change, drought and invasive species.”