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Aldabra Atoll - environment


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Aldabra was designated a World Heritage Site by UNESCO in 1982 as a prime example of a raised coral atoll and is significantly less disturbed than most other atolls in the Indian Ocean and elsewhere in the world.

The site is classed under category Ia (Strict Nature Reserve) of the IUCN Management Category and designated as a Natural World Heritage Site for fulfilling the criteria ii, iii and iv.

The status of Strict Nature Reserve of Aldabra has been associated with the fact that the atoll fits the following criteria:

 - It is an outstanding example representing significant on-going ecological and biological processes

 - Aldabra contains superlative natural phenomena or areas of exceptional natural beauty

 - Aldabra contains the most significant natural habitats for in-situ conservation of biological diversity

Aldabra’s unique ecosystems and species make it ecologically and scientifically valuable. Aldabra is the largest raised coral atoll on Earth and is significantly less disturbed than most other atolls in the Indian Ocean and elsewhere in the world. Aldabra is a refuge for many endangered species. These include the giant tortoise (Aldabrachelys gigantea); one of the largest congregations of nesting green turtles (Chelonia mydas) in the Indian Ocean; the world’s second largest breeding population of greater and lesser frigate birds (Fregata minor and Fregata ariel); the last flightless bird species in the Indian Ocean - the white-throated  rail (Dryolimnas cuvieri aldabranus); and a number of endemic taxa of plants and animals.

Long term monitoring programmes


Rainfall monitoring
Records of rainfall are extremely important for all aspects of science and conservation on Aldabra. Complete rainfall records can help explain population cycles, animal behavioural patterns and many other dynamics that occur on Aldabra. Nearly all aspects of Aldabra are somehow affected by the amount of precipitation, making the regular recording of rain gauge readings a top monitoring priority.

Tortoise monitoring
The status of the tortoise monitoring programme was reviewed during the tortoise population study conducted by ERGO (Environmental Research Group Oxford) at the end of 1997. The review concluded that the basic method of transect sampling is the most appropriate means of monitoring the various sub-populations of tortoise on Aldabra.

A total of twelve transects are monitored on a monthly basis. Three of these transects were established in the late 1970s in the Cinq Cases region, and the other nine were established in 1995 at various sites on Grande Terre, Malabar and Picard.

The primary objective of the tortoise monitoring programme is to provide information required for better understanding, management and conservation of Aldabra’s giant tortoise population. Regular assessments of the tortoise population, including the sub-populations on Grande Terre, Malabar and Picard, together with maintenance of long-term records and a computer database, will allow for identification and examination of major changes and trends in population size and structure. This in turn allows periodic review of management implications and options.

Turtle monitoring
The nesting of Green Turtles (Chelonia mydas) was monitored sporadically on Aldabra between 1968 and 1981, and more consistently using standard methodologies for morning beach surveys and nightly turtle tagging since 1981 (Mortimer 1988). Studies of growth rates and migrations in foraging populations of immature hawksbill turtles (Eretmochelys imbricata) have been ongoing since 1987.

Three types of turtle monitoring are conducted on Aldabra: a) morning beach surveys to count turtle tracks; b) nightly tagging of turtles; and c) tagging and measuring of immature foraging populations within the lagoon. Beach surveys give us an overview of various aspects of nesting activity on Aldabra including: its spatial distribution around the atoll; the seasonality of nesting within the calendar year; and how nesting activity fluctuates from one year to another. With these data we can better understand the status of the nesting population - whether it is increasing, decreasing or stable.

By tagging nesting females we learn about aspects of turtle behaviour that include: nesting site fidelity; nesting frequency within a nesting season (how many clutches laid and how many days between nestings); how many years separate the nesting seasons of individual turtles; and locations of distant foraging grounds for the population. International tag returns provide an index of the rates at which turtles are slaughtered at these foraging grounds.
Monitoring the foraging populations of immature turtles in the lagoon reveals information on the size and distribution of the population, growth rates, and migrations.

Coccid monitoring
The coccid (mealy bug), Icerya seychellarum, was introduced accidentally sometime in the 1960s and impacted the vegetation extensively, threatening the survival of some woody species. Surveys and research were conducted during the late 1970s by Newbery and Hill, and a monitoring programme was set up in 1980. In the late 1980s a coccinelid (ladybird) Rodolia chermesina was introduced as a biological control agent.

The main purpose of the coccid monitoring program has been to assess the level of infestation of Icerya on various woody plant species and to reveal any coccid population fluctuations which might occur. It also aimed to assess the effectiveness of Rodolia as a biological control agent on Aldabra.
These assessments were needed for management purposes. Scientifically it has also been an unusual study of an insect pest invasion in a relatively undisturbed environment where other factors are also being monitored.  The ongoing has been curtailed and the accumulated data now require full analysis.

White-throated rail monitoring
The white-throated rail (Dryolimnas cuvieri aldabranus) is the last “flightless” avian species in the Indian Ocean. Populations currently occur on Malabar and Polymnie islands, as well as a newly introduced population on Picard. In 1995 a monitoring programme was set up by Augeri and Pierce to census some of the main sub-populations. The collected data formed a useful baseline assessment of the rail population on Aldabra prior to a full scale scientific study of the rail which resulted in the successful reintroduction of the bird on Picard.

Vegetation monitoring
The monitoring of vegetation is important because so many terrestrial organisms depend on plants and their productivity, either directly or indirectly. “The dominant factors explaining the species composition of Aldabra’s vegetation are the degree of influence from salty ground water and the degree of shelter from the salt laden south-east trade winds, which blow for a significant proportion of the year” (ERGO 1997). Vegetation transects were established by Gibson and Phillipson (1983) in the Cinq Cases area, but they represent only a small sub-set of the mixed scrub vegetation in that part of the atoll. Some of these transects were re-sampled in 1988 by Scoones et al. (1989) and again in 1997 by the ERGO group (1997). Although the 1983 field studies were carried out in the rainy season, the 1988 and 1997 surveys were undertaken in the dry season, when many ground flora species are not detectable and some woody species lose their leaves and are difficult to identify.

There is a need, therefore, to repeat the four transects which were surveyed in 1997 during the rainy season. Vegetation monitoring generally only needs to be undertaken every five to ten years, preferably in the wet season.

Subsistence fishing monitoring
The purpose of the fish monitoring programme is to obtain information on the types, numbers and weight of fish caught around Aldabra for consumption purposes. Petrol consumption, the number of people fishing and the number of hours spent fishing are recorded so that an indication of “fishing effort” can be gained for different sites and different months of the year.

The results can also be analysed to reveal spatial and temporal trends in, for example, relative densities and size ranges of different edible fish species. Such information can be used for management purposes (for example, reducing the pressure on certain target species) as well as providing useful information for the scientific understanding of edible fish populations.

Beach erosion and accretion
A new programme was established by Augeri and Pierce in 1995 to quantify beach loss and accretion. The study began by focusing primarily on key turtle nesting beaches to help researchers quantify any correlation or causal relationships with seasonal and long-term shifts in nesting activity around the atoll.

In addition to quantitative measurements one of the best methods for evaluating and monitoring beach loss is through photographic benchmarks.
The main purpose of monitoring of beach erosion and accretion is:

  1. To help quantify any long-term changes in coastal zone habitats.

  2. To quantify beach dynamics relative to critical turtle nesting habitat.

  3. Photographic benchmarks will provide reliable references for both management actions and scientific studies.

Opportunistic monitoring


Bird monitoring

In addition to the species studied in the regular long-term monitoring programmes, there are several species that merit continuous but non-regular investigation.  Due to time restrictions and resource limitations programme priorities are established. However recognizing the importance of other species to Aldabra, efforts are made to record observations whenever possible.

Whenever SIF staff or visiting scientists are in the field they are required to record all unusual, rare, or scientifically interesting phenomena. Staff and visitors are also encouraged to note and report anything of interest to the Island Management, who can fill in an appropriate record card or computer record for the Aldabra database.

Newer monitoring programs include regular land bird point counts and shorebird counts

Greater flamingos 
 A pair of greater flamingos (Phoenicopterus ruber) with a grey chick of the season was sighted at an unnamed bassin in the Takamaka region of East Grande Terre. This was the first known record of flamingo breeding on Aldabra and the chick was observed several months later at Bassin Flamant with the flock. It is still unknown whether breeding is sporadic or annual, but this breeding discovery gives Aldabra the unique distinction of being the only coral atoll in the world where this species breeds.

Flamingos have been observed in flocks of up to 500 birds according to Skerrett (see Amin, Willetts and Skerrett 1995), although recent censuses show a maximum of 37 birds in one flock (Research Officer Report 2005). If this small population is resident on the atoll, rather than migratory, information is needed on its adaptations to Aldabra, its demographics and basic ecology. As there is increasing pressure to view and film this species on Aldabra, such information can be invaluable for management purposes.

Caspian terns
Caspian terns (Sterna caspia) are annual resident breeders on Aldabra, which makes the atoll the only oceanic site in the world where they breed. However, as a result of the nature and location of their very exposed ground nests at or below the high water line, low chick survival rates occur, often due to environmental conditions and predation. This situation makes it necessary for more data to be collected on Aldabra’s Caspian tern population of Aldabra.

Frigate birds
An experimental research project, initiated in 1995 by Augeri and Pierce, to test and analyse human/boat induced abandonment behaviour in frigate birds (Fregata ariel, F. minor), boobies (mainly Sula sula rubripes) and brown noddy (Anous stolidus) around the atoll, revealed very high abandonment by frigates, especially by females, when approached within 30m by boats with the engines on. Although fewer impacts were observed with some silent approaches at close distance, these inevitably led to even more abandonment because of the necessity to suddenly restart the boat engines due to currents or when leaving the area.

Abandonment of nests by frigate birds is potentially detrimental to both individual birds and to some of the colonies on Aldabra. Specific surveys at the more highly visited sites, conducted regularly, should reveal over time any changes in abundance or shifts in populations which might be due to the impact of visitation by humans.

Aldabra brush warbler
The Aldabra Brush Warbler (Nessilas aldabranus) is one of only two fully confirmed endemic avian species on Aldabra. It was last sighted in 1983 and may be extinct. If not, it is certainly one of the rarest birds in the world. The habitat in which it is found is densely covered with scrub vegetation, making sighting difficult. There is therefore a possibility the brush warbler still exists. The method recorded here is modified from the one developed by Augeri and Pierce (in which a warbler’s call was played continuously along the whole length of a transect as well as at 20m intervals).


Aldabra atoll is 400 km from the nearest mainland. There is little soil, practically no fresh water, no guano, no phosphate, no deep-water anchorage. The jagged coral can quickly tear shoes, and feet, to ribbons. The atoll is an inhospitable and even dangerous place. And therein lays its value to science. Over the centuries Aldabra has proved unattractive to sailors, fishermen, settlers and commercial interests. No other Indian Ocean island - and few islands anywhere in the world - has been spared human interference for so long.

Aldabra harbors a colony of 100,000 giant tortoises, endemic birds, insects, plants, coral reefs and fish that have survived as part of a unique ecological system undistorted by Man. This system was threatened with destruction in 1966, when Aldabra was still part of the British Indian Ocean Territory. Plans to build an airstrip for use by the British and American military were only abandoned after worldwide protests from conservation and research organisations, led in Great Britain by the Royal Society and in the United States by the Smithsonian Institution. As soon as the atoll came under threat, the Royal Society mounted a systematic programme of research in Aldabra and this continued when the atoll became part of the independent Republic of the Seychelles in 1976.

"An ideal location for the scientific study of evolutionary processes in a relatively closed biotic environment."

The preservation of Aldabra's unique ecosystem depends on international support. The atoll and its research station are managed by the Seychelles Islands Foundation a public trust established to safeguard the treasures of Aldabra and promote its use purely for research and education. SIF can fulfil this purpose with your support.


Tourism Regulations



1.  All vessels must have clearance in writing from SIF head office and the Seychelles Port Authority before visiting Aldabra. Vessels approaching Aldabra must identify themselves and when within one kilometre of the shore will be answerable to the Island Management of Aldabra. The vessel should select its anchorage or mooring within view of the research station and do so in an environmentally responsible way. Vessels should use mooring buoys if these are available. Access to the lagoon and landing on any part of the atoll other than in designated tourism areas is prohibited.
2.  Visiting vessels must remove all rubbish occasioned by their visit.
3.  All visitors must be accompanied by SIF staff at all times, except within the station grounds. Tour operator guides who are familiar with Aldabra and SIF policies, and have been vetted by SIF, may be allowed to lead small groups on permitted trails on Picard.
4.  Visitors are to remain on designated trails or when in open areas, within the limits set by their guide.
5.  Visitors, particularly film crews, must comply with their guide’s instructions regarding approaches to and viewing of animals and plants.
6.  Aldabra is a strict nature reserve. It is prohibited to remove shells or pieces of coral from any area visited.
7.  No biological or geological specimen, alive or dead, may be collected by any visitor.
8.  Fishing is not permitted within one kilometre from the shoreline. All boat operators should ensure that this restriction is conveyed to all their crew.
9.  Accidental introductions of alien species are a major problem in wilderness areas like Aldabra. Passengers and crew of cruise ships and charter boats are asked to assist in the prevention of this problem by always ensuring that they wear freshly laundered trousers and socks, and that their shoes have clean treads.
10. Diving and snorkelling groups shall use only those areas designated and shall be in groups of five or less per guide, except when snorkelling along the reef off the research station where the expedition leader should decide on the safe number per guide.
11. Standing on or handling coral or any other marine life is strictly prohibited.
12. All expedition leaders must conduct a short course for their clients on low impact snorkelling before they enter Aldabra’s coral reefs, marine and lagoon system.
13. Boats and zodiacs entering the lagoon to visit the frigate colonies must stay in close contact with the SIF lead boat. Zodiac drivers must at all times endeavour to keep outboard engine noise to a minimum when within the bird colonies. Mufflers should be used if possible. No-one is allowed to leave the boat.
14. It is prohibited to approach closer than ten metres to birds roosting or nesting.
15. Giant tortoises should not be stroked, patted or otherwise disturbed except at the research station where one or two individual tortoises are used to humans. It is strictly forbidden to sit on or ride any tortoise.

Visiting Aldabra

The Policy
Aldabra is a strict nature reserve and visitors to the atoll must receive authorisation from SIF. Request for authorisation can be made by contacting the SIF Head Office on the contact details provided.

The SIF policy on tourism at Aldabra is to increase the revenue raised by the SIF in order to support the protection and conservation of the atoll through limited and strictly controlled tourism with a focus on nature tourism and education.

Tourism activities are limted to the following operations:

 - Small to medium size cruise ship tourism.

 - Live-aboard charter boats and private yachts.

 - Live-aboard dive boats.

 - Land-based educational and scientific visits limited to 12 persons at any one time.

Access by a visitor to various parts of Aldabra is limited to the areas defined in the zoning policy and is conducted in a sustainable manner with impact being continually assessed.

Visitors are not allowed to collect shells or to damage or interfere with the plants and animals. No biological or geological specimen can be collected by any visitor. Visitors are also required to abide to sanitary measures to avoid introducing alien plant seeds.

All visitors to Aldabra must at all times be accompanied by an Aldabra staff member. It is not permitted to wander about unsupervised.

Getting there

1.   Aldabra is normally accessible from the main Island of Mahé through a bi-monthly supply boat belonging to the Island Development Company  (IDC). Otherwise, a plane can be hired from the same company to Assumption.  Transfer from Assumption to Aldabra and vice versa would need to be arranged on a specially chartered boat.
 2.   A visitor can also hire his/her own yacht on Mahé to visit Aldabra after receiving the authorization from the Seychelles Islands Foundation and the Port Authority.
With the obvious exceptions of cruise ships, private charter boats and private yachts, all other tourism access is dependent upon air connections between Mahé and Assumption and subsequent boat connections to Aldabra. While SIF may assist with such arrangements if the supply boat is in the area, it is not SIF policy to be involved in the establishment of the boat connection between Assumption and Aldabra.

Fees payable
All visitors are required to pay various fees for each day that a visitor remains at Aldabra.

For professional photographers and journalists a photography/filming fee will be applied for still photography and cine/video photography.

For further information on these fees please contact SIF on This email address is being protected from spambots. You need JavaScript enabled to view it.

Source: Seychelles Island Foundation (SIF)