The Nature Protection Trust of Seychelles, 53 River Lane, Cambridge CB5 8HP
Presented at the Symposium at the University of Bristol, 19 April 1997
"Only wee fouwnde heere good store of cocos, some fresh fyshe .... and tutles of so huge a bidgness which men will think incredible; of which our company had small lust to eate of, beinge such huge defourmed creatures and footed with five clawes lyke a beare." This was the scene that met the first people to land on the Seychelles Islands as described by William Revett in 1616 (Foster 1905). More detailed accounts written in the late 18th century describe abundant giant tortoises on all the islands and seas teeming with turtles, as well as with sharks and crocodiles (de Malavois in Fauvel 1909); the latter were killed on sight and had disappeared by the start of the 19th century (Gerlach & Canning 1994). Nearly 70 years after discovery a settlement was established on the islands and extensive plantations established. Inevitably this reptilian paradise was rapidly exploited and today the species noted by the early explorers are on the edge of extinction.
The Seychelles are an isolated group of diverse islands scattered across the western Indian Ocean. The main part of the group are the northern granitic islands. These high islands are covered by tropical rain-forest and support the main part of the human population of 70,000. Their great biological significance is that they are the peaks of submerged mountains left in isolation as India, Madagascar and Africa separated 100 million years ago. With this ancient history they support numerous animal and plant species that died out on the larger continents many millions of years ago and the dominance of reptiles in Seychelles is like a distant memory of prehistoric times. To the south there is an arc of coralline islands that ends with the Aldabra group of atolls. These rest on submerged volcanoes and support a more conventional island fauna and flora. The species on these islands are colonists from the nearby land masses of Africa and Madagascar. These low sandy islands are the main nesting areas for the marine turtles that swim throughout the tropics and sub-tropics.
Two turtle species breed in Seychelles; the Green (Chelonia mydas) and hawksbill (eretmocholys imbricate). Green turtles mainly nest in the southern islands where some tens of thousands come up each year. Historically these were exploited for their meat in vast numbers (Seychelles was at one time the main source of meat for the British turtle-soup industry) and this has caused their virtual extinction in the granitic islands. The isolation of the southern islands has protected the turtles there to some extent and all marine turtles are now protected by law. However, poaching remains a big problem. Greens and Hawksbills are rarely found nesting together in significant numbers and Hawksbills are mainly restricted to the granitic islands. Here they have suffered greatly due to trade in tortoise-shell. The complete protection of marine turtles in 1994 has been effective in halting this trade but this has been replaced by other threats. Hawksbills are now being poached for their meat and recent increases in the rate of development have resulted in threats to nesting beaches. This has now reached the situation where the only secure nesting sites are in nature reserves. These sites are actually showing signs of increased nesting activity and it is to be hoped that they can retain viable turtle populations in the face of the general declines facing these unfortunate animals (Gerlach 1997).
The granitic islands also support terrapins. Their presence there is something of a mystery. As they are represented by endemic species or subspecies they cannot be the result of recent introductions and are therefore the only natural terrapin populations on oceanic islands anywhere in the world. This may indicate that these mud turtles have very ancient origins. The species present include an endemic subspecies of black mud turtle (Pelusios subnigerparietals) which is found in coastal marshes. There is also an endemic subspecies of yellow-bellied mud turtle (P castanoides intergularis) which is mainly found in lowland streams. It is claimed that a third species is present the endemic Seychelles terrapin (P seychellensis). This is known from three specimens collected in 1894 and a fourth was reported exactly I 00 years later. Recent survey work has failed to confirm the survival of this species although numerous intermediates between it and the yellow-bellied mud turtle were found. It is not clear whether the Seychelles terrapin was a true species which has now been lost through hybridization or just a well marked variety of the yellow-bellied mud turtle. Whatever its status it now appears to be extinct (Gerlach 1997).
In the last year another species was added to the Seychelles list. Released red-eared sliders (Trachemys scripta elegans) have been found in the wild at two sites. No breeding has been noted but as both males and females have been found it is probably only a matter of time before they become properly established. It is not known how much of a threat they represent to the native species. These are already critically endangered with threats including drainage and pollution of their natural marshland and river habitats. In 1996 a major threat was identified. This is the destruction of marsh ecosystems by water lettuce (Pistia stratiotes). This plant has only recently been introduced to Seychelles but has already caused the stagnation of the largest fresh-water marsh area in Seychelles. Trial clearance work has been attempted in one small marsh but the problem is probably too far advanced to be dealt with manually. Unfortunately it will take some time before any alternative strategies (such as biological control) can be tried. On the large islands the large human populations are inevitably followed by large populations of dogs and cats. There is evidence that these introduced species are a problem to terrapin survival; a significant proportion of females and juveniles show tooth marks on the shells and the almost complete absence of hatchlings is probably due to nest predation by dogs or possibly by rats (Rattus rattus and R. norvuegicus) or tenrecs (Tenrec ecaudatus). The long term future of the Seychelles terrapins depends entirely on their presence in reserves where habitat destruction and predation can be minimised (Gerlach 1997). At present the yellow-bellied mud turtle is estimated to number 300-350 adults and the black mud-turtle 400-450 (Gerlach 1997). Of these only some 10-20 are found in reserves at present. In 1997 the Nature Protection Trust of Seychelles established a captive breeding programme to provide animals to restock reserve sites as the only means of ensuring their survival.
If Seychelles is associated in people's minds with any animal it must be the giant tortoise. These remarkable animals are unrelated to the more famous Galapagos giants and belong to a lineage that used to occur throughout the Seychelles islands, the Comoros and on Madagascar. It seems that they originated in the granitic islands of Seychelles, perhaps when the islands were the mountains of a microcontinent. There they evolved unique adaptations to allow them to drink through their noses, adaptations that gave them an advantage when colonising the dry south-west of Madagascar and the virtually water-less coral islands. This 'nasal drinking' allows them to drink from the shallowest and most temporary of puddles but they continue to use it even when water is plentiful and deep.
At the time of human colonisation of the islands tortoises were abundant on virtually every island, from the enormous atoll of Aldabra and the high granitic islands to the smallest rock or sand-bar (although there may have been confusion with turtles in some accounts) (Stoddart & Peake 1979). The tortoises provided the explorers with a useful source of meat and vast numbers were slaughtered or loaded onto ships. The size of the original population is not known but estimates of up to 300,000 can be made, extrapolating from the incomplete records. These granitic islands were soon exhausted and by 1840, after only 60 years of exploitation, tortoises were extinct in the wild. The same fate befell those on the outer islands and by 1880 only a small number survived on Aldabra atoll. Belatedly the tortoises were protected and the Aldabran population recovered from probably fewer than 1000 to its present level of 150,000 (Coe & Swingland 1984).
It has been generally assumed that the giant tortoise species which used to live in the granitic islands had all become extinct when the last survivors of the wild population died in 1875. Occasional suggestions that there may be survivors were greeted with scepticism arising from a very confused taxonomic situation (Bour 1984). A report of possible survivors in 1995 was accompanied by a skeleton which provided a unique opportunity to investigate these suggestions. Examination of museum specimens showed that there were significant differences between some captive animals and the surviving Aldabran species (Dipsochelys dussumieri). This provided the momentum for The Nature Protection Trust of Seychelles to be able to organise the Seychelles Giant Tortoise Identification Project. This involved a genetic study of a range of captive tortoises in Seychelles and the results confirmed that the majority of animals were the Aidabran species, as expected. In addition it supported the skeletal study in recognising survivors of one of the supposedly 'extinct' species (D. hololissa) and went further in providing evidence of the survival of a second Seychelles species (D. arnoldi) (Gerlach & Canning 1997). At present 8 individuals of D. hololissa and 6 D. arnoldi are known to survive. Of the three species known to have been present in the granitic islands one appears to be extinct whilst the other two have been rediscovered, having been on the brink of extinction for 150 years.
In 1997 the NPTS brought most of the survivors of these species into a captive breeding programme on Silhouette Island. The NPTS headquarters are on this island which is run as a reserve in conjunction with the NPTS. This conservation project aims to save these species from extinction. Our eventual aim is to increase the numbers of both species to secure levels and reintroduce them to reserves. Silhouette is the third largest and most natural of the granitic islands and may yet be a reptilian paradise regained.
The recent advances in the conservation of the Chelonia of Seychelles owes much to the supporters of The Nature Protection Trust of Seychelles and we are particularly grateful to the BCG and its members for their interest and support of both the giant tortoise and terrapin projects.
Bour, R. 1984. Les tortues terrestres geantes des iles de l'ocean Indien Occidental. Studia Geologica Salamanticensia 1; 17-76
Coe MJ & Swingland IR. 1984. Giant tortoises of the Seychelles. In Stoddart, DR. (Ed) Biogeography and ecology of the Seychelles Islands. Dr. W. Junk, The Hague. p.309-330
Fauvel, AA 1909. Unpublished documents of the history of the Seychelles Islands anterior to 1810. Government Printer, Mahe. 417pp.
Foster, W. (Ed.) . 1905. Thejournal of John Jourdain 1608-1617, describing his experiences in Arabia, India and the Malay Archipelago. Hakluyt Society, London. 394pp.
Gerlach, J. (Ed.). 1997. The Seychelles Red Data Book- 1997. NPTS, Seychelles.
Gerlach, J. & Canning, K.L. 1994. On the crocodiles of the western Indian Ocean. Phelsuma 2; 54-58
Gerlach, J. & Canning, K.L. 1997 (in press). A revision of the Dipsochelys giant tortoises. Chelonian Conseruation & Biology.
Stoddart, DR. & Peake, JF. 1979. Historical records of Indian Ocean giant Tortoise populations. Philosophical Transactions of the Royal Society, London B 286; 147-158
Testudo Volume Four Number Four 1997