Time to shell-ebrate! Giant tortoises thriving on Seychelles island

A big survey of the world's largest free-roaming giant tortoise population has found around 180,000 of them in one place - the highest figure ever recorded for the species.

The numbers of Aldabra giant tortoise - or Aldabrachelys gigantea - were counted on the island of Aldabra Atoll, one of Seychelles' most remote islands, in the Indian Ocean.

This is great news for the team and the tortoises, as this once endangered species now seems to be "thriving and stable".

The survey was carried out by the Seychelles Islands Foundation (SIF) and the University of Exeter.

The last survey in the late 1990s had recorded around 100,000 tortoises.

To reach this new total of 180,000 the team analysed five years of tortoise counts collected by SIF research staff between 2018 and 2022.

But researchers say that this new number doesn't mean the population has nearly doubled since 1999, as earlier surveys did not account for tortoises that were hidden in dense scrub or shade and so not seen by surveyors.

Dr Nancy Bunbury, one of the study's co-authors, said that while the island's thick vegetation makes counting tortoises difficult, "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".

She added that this new counting method, would establish "a benchmark we can use to track the population for decades to come".

The island of Aldabra Atoll became a strict nature reserve in 1981, a Unesco site in 1982, and has been called "one of the greatest conservation success stories of the Indian Ocean".

Despite the good news, the study's authors warn that vigilance is essential.

Invasive mammals like feral cats and black rats prey on tortoise eggs and hatchlings, but there are plans to try and remove these threats which could lift the last barriers to further growth of the population.

Aldabra's climate is changing and longer and more frequent droughts are predicted to reduce the shade and food available to tortoises, while rising sea levels threaten low-lying parts of the island.

University of Exeter's Dr Dave Hudson, who helped create the counting method, said: "These results are great news for the tortoises and testament to the fantastic work done in the field - but it's important to remember that the numbers provide a baseline, not an endpoint.

"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."

Aldabra Atoll is one of only two places in the world where giant tortoises can be found in the wild.

There is a much smaller population resident in the Galapagos, in the Pacific Ocean off the coast of Ecuador in South America.