Jump to content


Photo
- - - - -

Aldabra


  • Please log in to reply
No replies to this topic

#1 Cybergoldfish

Cybergoldfish

    Sperm Whale

  • Member
  • PipPipPipPipPip
  • 1954 posts
  • Location:UK */Seychelles/Singapore
  • Interests:Don't include plankton

Posted 17 January 2003 - 05:31 PM

Aldabra: Eco-Time capsule
Text and Photos: Bob Whorton BBC Draft 1

At 38km long Aldabra represents the biggest, singular raised annular atoll in the world. Its ramparts so expansive the rest of the islands in the Seychelles would fit comfortably inside its enormous lagoon.

Having travelled the world for years I wondered why it took me quite so long to discover this amazing bastion of nature...

Aldabra has been described as a “poor man’s” Galapagos, despite its extremely rich and diverse wildlife on a par with the marine and terrestrial life found in the well documented Ecuadorian archipelago. While it is true Aldabra has received less public exposure creating relative anonymity its natural treasures were like jewels to the scientific community. This atoll, encompassing the world’s largest lagoon, was established as a World Heritage site in 1983 as a protective measure for the unique flora & fauna – above and below the water. Aldabra is managed by the Seychelles Island Foundation from Mahe under the watchful eye of Mr Guy Esperon the chief warden on site.

SB The Aldabra group – Aldabra, Assumption, Astove and Cosmoledo were discovered in the 8th century by Arab traders sailing from the coast of Africa en route to India. The chain of four atolls, located in the southern Indian Ocean, is actually three times closer to Madagascar than to the capital of the Seychelles, Mahe.
In terms of wildlife it is worlds apart, and what those early traders discovered was a prehistoric land like nothing they had seen – filled with giant tortoise, turtles, bats and rare birds. However, the uniqueness of the wildlife at that time was seen only to fulfil the requirements for fresh meat and its trading potential.

Until the introduction of a reliable air service the outer extremities of the Seychelles – atolls like the Aldabra group, were unknown except to the few scientific groups. The last three years have seen tremendous change, as the general public become more aware of the beauty within this atoll.

Aldabra has three main islands – Grande Terre, Picard and North – surrounded by a healthy-regenerating coral reef. Grande Terre; restricted to scientific personnel, is the stronghold of more than 180,000 giant tortoises, but several hundred have established on the scientific settlement island of Picard too, providing behavioural hilarities for visitors.
The tortoise population of Aldabra rises and falls with good and bad seasons of edible vegetation in competition with feral goats, pigs and rabbits. The evidence of bad times can be seen periodically whilst trekking inland in the shape of tortoise remains bleached white by the sun.
This giant tortoise reaching an average size of over 1.5m and weighing several hundred kilos is a very agile beast and a very capable swimmer – a fact that has allowed it to successfully colonise all of the local islands where it can find a suitable diet. It is not unusual to find a single set of tortoise tracks leading into the sea and none coming back!

Diving Potential Second to None

The reef topography differs enormously around the atoll, there is virtually little similarity connecting any of the sites. Aldabra is rich in dive sites – many of which remain undiscovered because of more than 100km of coastline, and limited exploratory time. Three main channels twice daily refresh the inner lagoon with the nutrient rich waters from the Indian Ocean.

The migrating habits of schooling fish are affected by this constant influx of nutrients; certain species even gather outside these channels to take advantage of the changes in micro-organism proliferation which promotes its own food chain. The schooling tendencies of the numerous fish species increase with spawning; triggered by various seasonal changes promoting species aggregation of the grandest order at selective locations around the atoll.

Diving excursions offered; as a result of these variables, differ throughout each 16-week season, but visitors are virtually guaranteed all manner of interesting marine life interactions involving everything from gobies and crabs to mantas, whale sharks and then some.

ALMOST LOST
Before Seychelles saw its independence (whilst still a British Indian Ocean territory) plans were put forward to turn Aldabra’s main Island ‘Grand Terre’ into a strategic military base complete with an enormous runway. Fortunately the scientific outcry was loud enough to prevent this travesty reaching fruition, which was good news for the tortoise but bad news for the Chagon’s!


Marine superhighways

The massive movement of water as a result of the various tidal changes within the lagoon produces some of the quickest diving known to man.

The broader, main channel in the south of the atoll typically produces the maximum rush, as speeds of seven knots have been measured on an incoming current. The steep walls at the mouth of this channel concentrate the full force of the tidal flow; and the floor has been etched into roadways by debris, such as rocks or boulders, dragged in and out by the tremendous force. Raised sections provided support for a mixture of coral growth, with overhangs giving shelter to nurse sharks and stingrays

The much narrower eastern channel was a favourite among divers who had joined this expedition onboard the vessel Indian Ocean Explorer. This dive begins at the outer edge of the raised reef lip, and descends into the current-carved interior of the channel.

“A dead spot exists at 9m - everything seems to stop, and then as if some invisible hand pushes us in the back off we go - From zero to five knots in the blink of an eye”

The water was crystal-clear, making the navigation around bends and rocky outcrops that much easier and enjoyable. I was amazed at the number of nurse sharks just lying along the channel’s floor, although trying to stop and get a picture proved difficult! Several large speckled stingrays ducked out of the current in small clefts in the channel wall. The ride stopped all too suddenly, as we ran out of “runway”, and towards the end of the channel we were quickly picked up by the vigilant zodiac crew.


SB Catching some Rays

In front of the shallow side of the eastern channel is an area of brilliant white sand which splits the reef in two. The reflected sunshine was almost unbearable on the eyes, but underwater it served as a great place for observing stingrays in transit between the outer reef and the lagoon.

The rays had congregated on a broad circular stretch of sand in 7–8m of water, seven rays were positioned head to head, with only eyes and slender tails visible, sticking upwards from the sand – looking like a bizarre bear trap. Three kinds of ray’ resident in the area: common stingrays, fantailed rays and the smaller sand whip-ray.

Nute-chutes
To the north of the east channel is a gently sloping hard coral reef levelling off at around 20m on a flat sandy area. The strong cool upwelling in this area has carved the reef into valleys. Several ‘fingers’ of rock jut out into the blue, each densely covered in gorgonian fans unaffected by the cold water that had dissuaded hard coral growth. Porites corals were dominant (due to a lack of competition after El Nino) on the shallower inner reef, forming some ornate complex structures offering protection for a myriad of smaller reef fish. The many species of crabs were noticeably striking.


Walk-about

Excitement peaked when it was time to wander ashore for the first of our visits to Picard. Our timing meant a walk across the empty lagoon via the western channel, a walk which turned out to be amongst the most interesting 40 minutes of the trip, as even the smallest tide pools had something lurking inside. Morays and various crabs were bountiful.
Looking across the lagoon we were struck by the sheer size – it seemed at times that the horizon ended well before the atoll.
The constant ebb & flow of the tides has created bizarre natural limestone sculptures, adding surrealism to the landscape - as if we were gazing upon a real-time “Dali” interpretation arranged upon an infinite mirror.

Small tracks lead through the low tree line, and gave us our first glimpse of the giant tortoises that populate these islands. Hissing noisily as we approached, these mammoths were nonetheless shy, withdrawing their heads inside the shells as we approached.

The purpose-built scientific settlement is a sprawling affair, extending several hundred meters along the periphery below the high palms and native trees - accommodating staff and visiting scientists. There are also limited facilities for paying guests.

Scientific specialists working on the island at that time included Dr Jeanne Mortimer with the green turtles, and South African Ross Wanless researching the rare ‘Flightless Rail’ for a PhD. Ross agreed to show us the Rails he had reintroduced to Picard from north island that are now successfully breeding, I was privileged to be amongst the first photographers to capture images of newborn chicks – looking every bit like jet black chickens.

Beautiful Indian Sunbirds are resident here too, their iridescent green flanks flashing in the bright sunlight. The delicate nests of the sunbird can be found hanging from the low growing trees and bushes all over Picard Island.

Another interesting trek through the interior revealed that Picard has its very own miniature jellyfish pond too, measuring just 8m in diameter the pond supports around 100 ‘Cassiopeia’ jellyfish. Amazingly, there was a baby barracuda, a school of baby snapper and a large nudibranch in there too. Further inland is a much larger pool that is reputed to have a turtle trapped inside which according to form is surviving quite well. A labyrinth of tiny passages brings oxygenated water in and out from the sea during tidal changes, preventing evaporation & stagnation, and explains how the tiny life got so far inland.
These treks allowed observations of several Sacred Ibis scouring the interior for food and fighting amongst themselves for tastier morsels.

Between dives guided tours into the bird colonies amongst the mangroves were an interesting diversion. Both Booby’s and Frigate Birds nest here. A constant battle exists between the two for tree and airspace with the frigates intimidating the booby’s enough to have them eject their hard earned fish to be quickly re-swallowed by themselves.
The crystal clear shallow water allowed us the chance to see the passage of stingrays, bump-head parrots and turtles directly beneath the zodiac.

Snorkelling revealed even more day to day routines of the marine life amongst the mangrove roots including an encounter with mating nurse sharks in waist-deep water. All of this set amongst some incredible natural structures.

The lagoon in front of Picard was great for black-tipped sharks… it was possible to wade out to our knees and have up to a dozen swimming around us.


We were further privileged to observe the work of Dr Jeanne Mortimer (Reef’s Godmother) during a ‘Green turtle Conservation and monitoring program’.
Jeanne’s assistants spent their days catching the green turtles in the lagoon and bringing them ashore at the facility. Here the turtles undergo a complete examination that includes weighing, measuring, blood sampling (for DNA) and tagging.
Awaiting his turn at the clinic was a large male turtle missing its left motor fin - surgically removed by a shark a long time ago, the wound had perfectly healed, and apart from an obvious loss of traction it was causing no other problems... well, except from the psychological scars left by girl-turtles calling him ‘Stumpy’.
Unlike Sipadan, these turtles are difficult to observe closely in the water and this gave us an opportunity to do just that.

Aldabra for me was a wonderful experience, a breath of fresh air, so to speak: Allowing a privileged insight into the real goings on of scientific research programmes, and Mother Nature herself. Aldabra leaves its mark on every individual who visits her - not only for the underwater encounters but for its unique surface attributes too.