Aldabra's Giant Tortoises Counted at 183,000 in Five-Year Survey

Almost 183,000 adult and sub-adult Aldabra giant tortoises live on Aldabra Atoll in Seychelles, and the population stayed relatively stable during the study period. The estimate comes from five years of tortoise counts between 2018 and 2022. The survey was led by the Seychelles Islands Foundation and the University of Exeter. The Guardian

The study was published in the scientific journal Ecology and Evolution. The University of Exeter published its news report on the study on October 7, 2026. That report was written by Andrew Merrington. EurekAlert carried a news release titled "New study reports largest-ever population estimate for Seychelles' giant tortoises". The species studied is Aldabrachelys gigantea. University of Exeter

Rounded to about 180,000 animals, the figure is the highest ever recorded for this species. It updates the previous widely cited figure of 100,000 from the late 1990s. The count took five years to complete. Think of it like attendance taken across five school years rather than one morning. Stability across that series is the headline.

The number of tortoises on Aldabra far exceeds the human population of Seychelles. It was reported as the world's largest free-roaming giant tortoise population. Aldabra Atoll is one of only two places in the world where giant tortoises live in the wild. The other is the Galapagos, with a much smaller population.

In the 19th century, hunting and trade left fewer than 1,000 Aldabra tortoises on the island. Aldabra Atoll became a strict nature reserve in 1981 and a UNESCO site in 1982. That legal history now frames almost four decades of formal protection.

Earlier work documented tortoises introduced elsewhere in the island chain. A 1987 survey by H.J. Samour of the introduced population found 144 post-hatchlings, 1 juvenile and 17 hatchlings spread across 6 of 9 set areas on Curieuse. A 2026 preliminary study by A.M. Lavigne and colleagues gave the first population-level check of fertilization and hatching success in the Aldabra giant tortoise. In simple terms, how many eggs are fertilized and how many hatch.

Separately, Reuters reported that Jonathan, a 194-year-old tortoise, may hold clues to longer life. Jonathan is an Aldabra giant tortoise estimated to be about 194 years old. He is described as the world's oldest land animal. Reuters

The broader context here is what an updated baseline changes for managers and researchers. The late-1990s figure of 100,000 anchored policy discussion, funding plans and ecological models for nearly three decades. Replacing it with almost 183,000 adults and sub-adults, drawn from a multi-year count rather than a single-season estimate, narrows the range of uncertainty around density, recruitment of young into the adult group, and grazing effects on plants.

In my view, the pairing of results matters more than any single number. Adult abundance looks high and steady. The Curieuse hatchling map and the atoll-wide fertilization and hatching study point to where limits still sit. For a very long-lived animal that breeds late, adult counts alone can hide delayed effects. Linking the new estimate with breeding data would give a fuller life-table picture, from egg to hatchling to breeding adult.

Looking at what this means for comparative work, Aldabra and Galapagos remain the only wild systems for island gigantism in tortoises, where isolation favors very large body size. A firm Aldabra estimate clarifies that comparison. It also sharpens questions about carrying capacity, or how many the land can support, uneven numbers across the atoll, and the institutions behind the rise from fewer than 1,000 to about 180,000.