4 fascinating facts about Seychelles' Aldabra Atoll

A giant tortoise is seen nesting in the Aldabra, the world’s largest raised coral atoll in the Indian Ocean. Picture: Reuters

A giant tortoise is seen nesting in the Aldabra, the world’s largest raised coral atoll in the Indian Ocean. Picture: Reuters

Published Nov 16, 2023


The Aldabra Atoll was designated a Unesco World Heritage Site in December 1982.

The atoll is part of the outer islands of Seychelles and is one of the two heritage sites managed by the Seychelles Island Foundation (SIF).

The other World Heritage Site is the Vallee de Mai on the second most populated island of Praslin, a nature reserve where the endemic coco de mer grows in its natural state.

Aldabra is a raised coral atoll and is home to the largest giant tortoise population in the world.

The atoll has remained largely untouched by humans for the majority of its existence, due to its remoteness and inaccessibility.

SNA brings you four fascinating aspects about the atoll - designated due to its outstanding universal value.

History of Aldabra

It is reported that Arab seafarers were the ones who first discovered Aldabra during an exploratory trip in the Indian Ocean in 916 AD.

The name Aldabra is reported to have come from an Arabic word, and in 1509, the atoll Alhadra was shown on a Portuguese map of Madagascar.

In 1742, there was the first recorded visit to Aldabra, when the French Captain Lazard Picault seized the islands of Seychelles.

In 1814, Aldabra became part of the British colony, and in 1888 the first settlement was built on one of the atolls of Aldabra, as the atoll was leased for commercial activities.

It formed part of the British Indian Ocean Territory from 1965 until Seychelles' independence in 1976.

In 1971, the first research station was constructed on Aldabra by the UK-based Royal Society, and in 1979 the Seychelles Island Foundation (SIF) was set up by a presidential decree and took over the management of Aldabra.

The Royal Society handed over the research station to the foundation a year later.

Aldabra Atoll, one of Seychelles' most remote islands, is over 1,000km southwest of the main island of Mahe.

The Atoll

Aldabra is an enormous atoll and, at 35km by 15km, is the largest of the Seychelles islands, with a land area of around 155km2 and a total protected area of 2559km2 (including the lagoon, land, and marine protected area).

The largest inhabited island of Seychelles, Mahe, would fit in this lagoon.

Aldabra atoll, amongst the largest atolls in the world - is made up of four atolls, mainly Picard, Grand Terre, Malabar, and Polymnie.

The coral islands raised 8 metres above sea level, enclose a large lagoon and are surrounded by a coral reef with rich and diverse marine life.

Due to its remoteness, the atoll has remained more or less isolated with very little human interference making it an important natural habitat where the ecology and wildlife are pristine, a laboratory for researchers and scientists.

The main human settlement is on Picard, where a scientific research station was established.

The station is responsible for a long-term monitoring program that covers many aspects of the atoll's biodiversity and natural processes. Other related research and projects are done through the centre.

Aldabra giant tortoise

Aldabra is home to the endemic Aldabra giant tortoise and has the world's largest population of this species, estimated to be more than 150,000.

The tortoises are the last survivors of a life form once found on other Indian Ocean islands, and Aldabra is now their only remaining natural habitat.

The tortoises have been continuously monitored around the atoll since 1998 to assess seasonal distribution, patterns, size, and sex differences between these species between the islands.

Recent research projects were undertaken to improve understanding of the links between the Aldabra giant tortoises and their unique environment.

As part of an effort to introduce the species to other islands, in 1978, about 250 Aldabra giant tortoises were brought to Curieuse - a small granitic island close to the third-most populated island of Praslin.

Aldabra tortoises can reach a weight of up to 250 kilogrammes and are up to 150 years old. Jonathan, an endemic Aldabra giant tortoise living on the island of St Helena in the Atlantic, has been named the "oldest tortoise ever'' by Guinness World Records.

Jonathan was transported from Seychelles to St. Helena under the British administration in 1882 when he was approximately 50, making him 191 years old in 2023.

Aldabra – fauna and flora

Both land and sea, mangrove wetlands, and the coral reef are home to several species, some unique to the atoll.

Species include coconut crab, land and sea birds – some endemic to the islands, black tip reef sharks, green turtles, and hawksbill tortoises.

Aldabra has the second-largest population of nesting green turtles in the western Indian Ocean.

Pristine marine life and undisturbed beaches provide an ideal habitat for these reptiles. Green turtles are listed by the International Union for the Conservation of Nature (IUCN) as globally endangered due to severe declines in their numbers caused by hunting, fishing by-catch, and coastal habitat modification.

Aldabra's near pristine environment and ecology offers researchers, scientists, and nature lovers a living outdoor classroom and a natural world where several important animal species and some plant species thrive due to stringent conservation and protection measures, including protection by law and, not surprisingly, limited human interference.