The population of Aldabra giant tortoises on Aldabra Atoll in Seychelles has reached a record high of approximately 180,000 individuals, a figure that far exceeds the human population of Seychelles. This landmark survey confirms the species, once endangered, is now thriving in its free-roaming habitat.
The findings, led by the Seychelles Islands Foundation (SIF) and the University of Exeter, are the result of analysing five years of tortoise counts collected between 2018 and 2022. Published in the scientific journal Ecology and Evolution, this is the first rigorous, atoll-wide estimate since a widely cited figure of 100,000 tortoises from the late 1990s.
Record Population Figures Revealed
Researchers estimate the best figure for adult and sub-adult tortoises is almost 183,000. This new, higher figure does not imply the population has nearly doubled since the 1990s, according to the study’s authors. Earlier surveys likely underestimated numbers because they did not account for tortoises hidden in dense vegetation or shade. The new study used a sophisticated statistical technique, known as Bayesian hierarchical distance sampling, to correct for missed animals and differences in visibility across Aldabra’s diverse habitats, thereby providing a more reliable baseline.
Dr Nancy Bunbury, one of the study’s co-authors, highlighted the importance of this method, stating: “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.”
A Major Conservation Triumph
The recovery of the Aldabra giant tortoise is being hailed as one of the greatest conservation success stories of the Indian Ocean. In the 19th century, heavy exploitation reduced their numbers to fewer than 1,000 individuals on the island. Decades of conservation efforts, including Aldabra becoming a strict nature reserve in 1981 and a UNESCO World Heritage Site in 1982, have allowed the population to rebound.
Dr Frauke Fleischer-Dogley, CEO of SIF, expressed her pride in the achievement, saying: “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.” You can read more about this remarkable recovery on The Guardian.
Ongoing Threats and Future Vigilance
Despite the positive news, the study’s authors stress that vigilance is crucial. Aldabra’s climate is changing, with predictions of longer and more frequent droughts that could reduce available shade and food for the tortoises. Rising sea levels also pose a threat to low-lying parts of the atoll.
Invasive mammals, such as feral cats and black rats, remain a concern as they prey on tortoise eggs and hatchlings. Researchers suggest that the planned eradication of these remaining invasive mammals could remove the last barriers to further population growth and help the tortoises withstand future climate pressures.
Dr Dave Hudson, a postdoctoral research associate at the University of Exeter’s Cornwall campus, emphasised the ongoing nature of conservation. He stated: “But it’s important to remember that the numbers provide a baseline—not an endpoint.” He added that the study provides evidence for conservation managers to track future changes and act early as the tortoises face increasing pressures from climate change, drought, and invasive species. Further details on these challenges are available via Phys.org.
FAQ
- How many Aldabra giant tortoises are there now?
A recent survey estimates there are approximately 180,000 Aldabra giant tortoises, with a best estimate of almost 183,000 adult and sub-adult individuals, living on Aldabra Atoll in Seychelles.
- Where do Aldabra giant tortoises live in the wild?
The largest free-roaming population of Aldabra giant tortoises lives on Aldabra Atoll in Seychelles. A much smaller wild population also exists in the Galápagos.
- Why is this number considered a conservation success?
The population was reduced to fewer than 1,000 individuals in the 19th century due to exploitation. Their recovery, aided by protection since Aldabra became a strict nature reserve in 1981 and a UNESCO site in 1982, is now considered one of the greatest conservation success stories of the Indian Ocean.
- What challenges do the tortoises still face?
Despite their recovery, the tortoises face threats from climate change, including longer and more frequent droughts and rising sea levels. Invasive mammals like feral cats and black rats also prey on their eggs and hatchlings.
