VICTORIA (Realist English). Aldabra giant tortoises, once on the brink of extinction, now numerically exceed the population of the Seychelles. A new study estimates their population at nearly 183,000 adults. This is the highest figure in the entire history of observations.
From fewer than a thousand to a record 183,000
In the 19th century, due to uncontrolled harvesting by sailors and pirates, fewer than 1,000 giant tortoises remained on Aldabra Atoll. Today, after decades of protection, their numbers have reached nearly 183,000 adults and subadults. This is the first large-scale update of data since the late 1990s. At that time, the figure of 100,000 tortoises was widely cited.
The resulting estimate exceeds the population of the Seychelles. According to various data, it ranges from 102,000 to 135,000 people.
Why the numbers grew but did not double
Researchers warn: the new figure does not mean the population has nearly doubled since 1999. Previous counting methods did not account for tortoises hidden in dense vegetation or shade.
The new study, published in the journal Ecology and Evolution, applied Bayesian hierarchical distance sampling. This is a statistical method that adjusts data to account for unseen animals and differences in visibility across habitats. This made it possible to obtain the most reliable baseline estimate to date.
Key facts
Current population: about 183,000 adults and subadults.
Historical minimum (19th century): fewer than 1,000 individuals.
Previous estimate (1990s): about 100,000 individuals.
Protection status: strict nature reserve (1981), UNESCO site (1982).
Analysis period: 2018–2022.
Threats remain
Despite the success, scientists warn of the need for vigilance.
Climate change. Longer and more frequent droughts reduce food and shade. Rising sea levels threaten the low-lying parts of the atoll.
Invasive species. Feral cats and black rats eat tortoise eggs and hatchlings. Feral goats, which destroyed vegetation, were eradicated in 2012.
Plans. Eradicating the remaining invasive mammals could remove the last barriers to population growth.
Aldabra Atoll is one of two places in the world where giant tortoises live in the wild. The second is the Galapagos Islands, where the population is significantly smaller. The recovery of the Aldabra population is considered one of the greatest conservation success stories in the Indian Ocean.
