Giant tortoise count hits 183,000 on Seychelles island, study shows

As many as 183,000 giant tortoises thrive in the Seychelles, a new survey has found.

The Aldabra giant tortoise (Aldabrachelys gigantea) are said to be an endangered species. A survey led by the Seychelles Islands Foundation (SIF) and the University of Exeter found that the identified population is the “highest figure ever recorded for the species.” The discovery is a huge victory for conservation efforts across the Indian Ocean.

Population rise

The current population contrasts sharply with the late 19th century, when hunting and habitat exploitation nearly drove the reptiles to extinction. It left fewer than 1,000 survivors on the isolated coral ring.

Swift intervention reversed their decline after Aldabra was designated a strict nature reserve in 1981 and a UNESCO World Heritage site in 1982. Rigorous legal protection combined with the successful eradication of invasive feral goats in 2012 ultimately paved the way for this historic recovery.

“The monitoring data in this study were collected by SIF staff living and working on the atoll, year after year. More than 180,000 giant tortoises roaming freely on our atoll is proof of what long-term commitment to conservation can achieve. This is wonderful news for Seychelles, for the world, and for everyone who has worked to protect Aldabra,” said Dr Frauke Fleischer-Dogley, CEO of SIF.

A baseline for the future

However, determining the population count was not straightforward. It required almost five years of dedicated field monitoring by SIF researchers alongside statistical experts at the University of Exeter. The actual counting process proved to be a complex challenge.

Aldabra’s landscape consists of sharp coral and thick, tangled vegetation. Tortoises routinely seek shade under dense bushes, vanish into mangroves, or shelter from the scorching equatorial sun. Previous surveys relied on raw headcounts.

As a result, older estimates, such as the long-cited 100,000 figure from the late 1990s, likely missed tens of thousands of hidden animals.

To fix this, researchers used Bayesian hierarchical distance sampling. It is an advanced statistical method that models missing data. The technique mathematically corrects for unseen reptiles across different habitats, from open “tortoise turf” grasslands to impenetrable scrubland. Rather than a sudden surge, the new estimate shows the population has always been strong, thriving, and secure.

Despite the encouraging news, scientists stress that caution remains essential as the island’s fragile ecosystem faces serious environmental threats. Rising sea levels risk submerging low-lying habitats, and increasingly severe droughts threaten to dry up food and shade. Also, invasive rats and cats continue to prey on vulnerable tortoise eggs and hatchlings. Together, these threats underscore the need for ongoing protective measures.

“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,” said Dr Nancy Bunbury, one of the study’s co-authors.

Plans to eradicate the remaining invasive mammals is already underway. But for meantime, Aldabra Atoll offers a rare story of hope, showing a landscape where nature rebounded from near collapse and giant tortoises reclaimed their habitat.

The study findings were published in the journal Ecology and Evolution

Source: https://interestingengineering.com/science/giant-tortoise-count-seychelles-island