Page last updated at 12:00 GMT, Saturday, 8 January 2011

Seychelles tortoises: Giants ruling the Aldabra lagoon

By Tim Ecott

Aldabra lagoon
Aldabra is one of the most important habitats for evolutionary study

The inaccessible Aldabra lagoon in the Indian Ocean is a Unesco World Heritage Site and home to a unique collection of plants and animals, including more than 100,000 giant tortoises.

For three hours, the island supply plane cruises above the seemingly empty blue plain of the Indian Ocean.

At Assumption Island, there is an airstrip where we transfer to a motorboat for the crossing to Aldabra.

Visitors are infrequent... Somali pirate activity has reduced that market to almost zero

Lindsay Chong Seng, science director for the Seychelles Islands Foundation, is my guide and, after an hour on the sparkling sea, he points out a long, low strip of rugged shoreline.

It is South Island, the largest of the four main islands surrounding the great central lagoon.

The lagoon is shallow, a place of ripping currents and vast sand flats, and is so big that the whole of Manhattan could fit inside it - twice.

'Shark-infested waters'

Stepping from the back of the speedboat into gin-clear water up to my knees, I see I am not alone.

Dozens of black-tip sharks cluster in the shallows, and among them are larger lemon sharks - each over seven feet (two metres) long.

Sharks in the lagoon
Its isolation means the lagoon is free from overfishing and pollution

The splashing of our feet sounds, I am told, like the noise an injured fish might make and the sharks come to investigate.

Once close enough to see that I am human, they dart away skittish and alarmed, their pale dorsal fins sticking out of the water like the very cartoon image of "shark-infested water".

There is no hotel here, although the expense of running the island and staffing it means that the idea is sometimes proposed.

Visitors are infrequent - just a few yachtsmen. Until last year, there was the occasional small cruise ship, but Somali pirate activity has reduced that market to almost zero.

In fact, a few months ago, some pirates landed on the beach having run out of food and water.

With the help of the rifles the rangers use to shoot feral goats, the pirates were arrested, locked in a store room and sent back to the capital, Victoria.

Dominant reptiles

Outside the small research block, island manager Doctor Nancy Bunbury introduces me to the first of the Aldabra giant tortoises.

"Please don't feed him," she warns, "or he'll follow you into our dining room. And if he doesn't want to leave, it becomes a bit of a problem."

Giant tortoise
Aldabra's giant tortoise population is the largest in the world

Once harvested for meat and exported to the inhabited islands, the tortoises can weigh over 600lb (300kg). Standing fully upright on all four leathery legs, their heads reach easily to my waist.

Lindsay Chong Seng explains that they will eat anything including other dead tortoises, any vegetation they can reach and, intriguingly, a kind of algae which they seem to cultivate by leaving their droppings in tidal pools.

As well as hungry tortoises, Aldabra's scrubby vegetation also has to cope with salt spray, thin soil and cyclones.

One endemic grass has even evolved so that its flower-spikes turn downwards from the stem so that the reptiles do not eat it while they are grazing.

With at least 100,000 giant tortoises - 10 times as many as in the Galapagos - Aldabra is valued by biologists as an ecosystem dominated by reptiles, something that has not been seen elsewhere since the time of the dinosaurs.

Isolation makes Aldabra's wildlife bold.

Fluffy Aldabra nightjars nest on the ground, fearlessly allowing me to lie right beside them with my camera.

A small elegant bird with big feet and a russet plumage stalks the undergrowth. Lindsay names it as the white-throated Aldabran rail, the last flightless bird in the Indian Ocean.

One day I watch as a rail discovers a baby giant tortoise - smaller than my palm - and attempts to peck at it. The tortoise does what tortoises do and retreats inside its shell until the rail loses interest.

It will need to avoid not just the rails, but also the two species of land crabs that live on Aldabra, including the coconut crab with a leg span of more than three feet (1m) and weighing up to 10lb (4.5kg).

At night, they stalk the accommodation block and I learn to carry a torch.

Another world

On excursions into the lagoon and along the mangrove-forested shore, I see frigate birds, crab plovers, dimorphic egrets, green herons and plenty more sharks.

Map of Seychelles

At slack tide, it is hard to tell which way lies the open sea and which way the lagoon.

I feel as though I am in another world, a place where nature has been left to take its course. The water sparkles, the sand is as white as the clouds above and the undergrowth crackles as the crabs and tortoises patrol.

Seychelles protects Aldabra by subsidising the ranger's station and science facilities here with income from the Vallee de Mai - another Unesco World Heritage Site on the island of Praslin that is easily accessed by tourists.

It is home to Seychelles' unique double coconut - the coco-de-mer, the tree with the largest seed in the plant kingdom.

They may not know it but those day-trippers are paying to keep Aldabra free of visitors and a safe haven for a unique collection of plants and animals which few people will ever see.

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Country profile: Seychelles
21 May 11 |  Country profiles

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