Return of the dinosaurs: Aldabra Giant Tortoises roaming free on Alphonse |27 November 2023
On a quiet morning on Alphonse Island, loud booming sounds can be heard from afar; a hiss and a rustle come out from a game path in the forest; large piles of dung, full of seeds from indigenous plants can be seen among the grass. These are the signs that giants are roaming free among us.
The Aldabra Giant Tortoise, ‘Torti-d-Ter’ in Creole, are one of the two remaining species of giant tortoise in the world. They grow to over 300kg and can live close to 200 years. The Seychelles and its 115 islands evolved with these animals, their environments being shaped by the reptile’s movements. Like elephants on the African savannah, they are what is known as a Keystone Species. By dispersing seeds, disturbing soil, trampling over small tree saplings and grazing, they can keep areas open, allowing smaller species of scrub and grasses to thrive, engineering a mosaic of habitats that other indigenous animal species depend on.
Their ability to survive long periods without fresh water or food was a great asset for colonising distant islands in a pre-human world. That became their Achilles heel, however, when humans began to explore these remote islands. Being able to survive long voyages in a ship's hold meant that passing vessels would take as many as they could fit, ensuring fresh meat for the duration of their long sea voyages. This intense pressure emptied these islands of their tortoise populations, causing several distinct species to go extinct and robbing these islands of their influence. All that remained were those on Aldabra, saved by its remoteness and rugged terrain. It is from this population, hundreds of years later, that Alphonse and many other islands have reintroduced tortoises, allowing them to help in healing these ecosystems after centuries of exploitation and change.
In 1999, the hotel on Alphonse brought over a group of 12 individuals from Aldabra, keeping them in a large enclosure. It wasn’t until 2007, when the Island Conservation Society (ICS) started working on the island, that the decision was made to release the group and allow them to roam free on the island for the first time in hundreds of years. In the ensuing years since that release, ICS has brought other individuals over from various sources, boosting the genetic diversity and strengthening the population. They soon started breeding, laying their eggs in large holes they dig with their specifically adapted long-clawed hind legs, enabling the population to grow and grow. When a small hatchling is found, the vulnerable tortoise is placed in a specifically built nursery, protected from predators such as herons and rats. There it remains, regularly monitored by the ICS team, checking its health and growth rates, until it reaches a suitable size to be released. On release, it is tagged for future identification and then left to begin its life in the wild, impacting the vegetation around it.
To date, Alphonse has a known population of 105 giant tortoises, including 77 tagged and free-roaming individuals. This number is continuously rising as the adult population increases and breeds and more hatchlings are discovered. There are almost certainly many more, however, hidden in the dense forests that have avoided detection. Through regular monitoring, the team can start to get a picture of where individuals spend their time and how this charismatic species might be influencing their altered environment. This is vital information that can be shared with other islands looking to reintroduce tortoises and restore their island’s ecosystem. With every reintroduction, this giant species can have a giant impact on the islands of Seychelles.
Contributed by Jack Coupland
ICS conservation officer, Alphonse
