TRISTAN DA CUNHA

by Michael Swales, Curator, Tristan Resource Centre

After days at sea, butting into the southwesterly swell, there is a sense of keen anticipation as the mountainous shape of Tristan da Cunha comes eventually into sight. For Tristan (as it is more familiarly known) lays claim to being the most isolated inhabited island in the world. Situated in the middle of the South Atlantic Ocean it is almost on the same latitude as the Cape of Good Hope, 2900km away. The nearest part of South America is 3200km to the West. Tristan is on the edge of the Roaring Forties and so has a rough, often severe, but generally mild oceanic climate.

Geologically, Tristan is situated towards the southern end of the mid-Atlantic Ridge and consists of a group of six islands, volcanic in origin, the oldest dating from about 22m years ago. Only the nominate one is still active and has the typical cone shape, being about 13km in diameter at sea level. The other islands are much eroded and smaller; four of them (Inaccessible, Nightingale, Stoltenhoff and Middle) are grouped 38-40km to the southwest; the fifth (Gough Island) is some 350km to the South of the main island.

Tristan da Cunha was discovered by the Portuguese in 1506 and named after their Admiral. Over the ensuing centuries, the islands were visited regularly by sealers to exploit an abundant resource. Ships also called for freshwater on their way to the East Indies. An unsuccessful attempt was made at colonisation at the beginning of the 19th century; but the first official settlers stayed after annexation by the British in 1816. An army garrison was stationed there when Napoleon was imprisoned on St. Helena, but was withdrawn before his death. It was then that Cpl. William Glass was granted permission to stay with his family and thus founded a new death. It was then that Cpl. William Glass was granted permission to stay with his family and thus founded a new island colony. Numbers increased steadily, though with fluctuations, and were added to by settlers from shipwrecks; but the total has never exceeded 300 and still includes only eight family names.

Human survival on Tristan has never been easy and the island most recently came to the world's attention in 1961 when the volcano erupted. All the inhabitants had to evacuated and it was two years before it was safe for them to return. Tristan da Cunha is a Dependency of St. Helena, 2400km to the North, and governed by the Foreign and Commonwealth Office through a resident Administrator who is advised by an Island Council of eight elected and three appointed members. The economy is based on a regulated crayfishery and revenue derived from philatelic and handicraft sales.

FAUNA & FLORA

Tristan supports five native vegetation types zoned according to altitude and topography. The coastal strip originally had vegetation dominated by Tussock Grass and fern bush interspersed with the Island Tree (Phylica arborea). Except on exposed cliffs beyond the reach of grazing animals, tussock has largely been lost. Wet heath occurs at higher altitudes and moss and feldmark on the upper slopes. Bog and swamp vegetation occupies suitable depressions. Inaccessible has three vegetation types: tussock grass, fern bush and a few freshwater bogs, little affected by human activities. Nightingale is covered by dense tussock grass. Gough has similar vegetation types to those of Tristan and they remain virtually undisturbed.

There are 212 vascular plant taxa recorded, including 35 native ferns and 58 native flowering plants. Of these, 20 fern and 34 flowering plant taxa are considered to be endemic. Six of these endemics are classified as Rare, but few if any of the taxa are immediately threatened. Phylica arborea is recovering on cliffs above the Settlement Plain in Tristan following a ban on cutting instigated by the Island Council.

The Tristan group does support an invertebrate fauna, with weevils and snails of particular interest, but has a relatively low number of native species. Reptiles and amphibians are not present. There is a total of 28 breeding landbirds of which six are endemic. The islands have been called a minature Galapagos because of the radiation among the endemic Nesospiza finches. Nevertheless, it is the seabird colonies found in Tristan that are of international importance. The nominate subspecies of Yellow-nosed Albatross and the Atlantic Petrel are endemic to the Tristan group and Gough Island. The Great Shearwater is virtually endemic to the same islands and a race of White-chinned Petrel is confined to Inaccessible. In the past, Tristan islanders have taken Northern Rockhopper Penguins, Yellow-nosed and Sooty Albatrosses and Great Shearwaters, but economic factors and conservation legislation are reducing seabird exploitation. There are still traditional longboat trips to Nightingale to collect early season penguin and shearwater eggs and subsequently shearwater chicks; the present annual toll poses no immediate threat to the populations.

Two species of seal, Fur and Elephant, are native. They have been exploited in the past but are now protected, and the fur seals in particular are increasing in numbers once more. Two whales occur relatively frequently in Tristan waters, the Southern Right Whale and the Sperm Whale, and various species of dolphin are common.

CONSERVATION

The first full scientific expedition to Tristan da Cunha was the Norwegian one of 1937-38. This produced the first accurate map of the main island and, although members were unable to visit all the others, drew attention to the uniqueness of much of the fauna and flora. It was not until 1955-56 that the next took place; the Gough Island Scientific Survey in similar manner produced the first map of that island and highlighted the exceptionally rich and unspoilt biota. Another result was to demonstrate the potential benefit for South Africa of sending regular weather reports from there, resulting in the establishment of a manned meteorological station on Gough. The Royal Society sent an expedition to investigate the volcanic eruption in 1962 which led to further interest in the geology. In 1982-83, the Denstone Expedition to Inaccessible Island produced the first shore-based map of that island and further documented the biota. Other, smaller follow-up expeditions from Britain and South Africa, have taken place since.

All this attention from scientists, resulting in an increasing number of research papers, has emphasised the importance of Tristan da Cunha as among the last unspoilt places on earth. This in turn has led to a concern to conserve, with appropriate policies instigated and enforced by both the Island Council and the British Government. Since only the main island is inhabited the greatest effects of human activity are to be found there. These include the consequences of agriculture - overgrazing by sheep, tree removal and fire - and threats from introduced species. Indeed, it is vital to keep all the islands free from alien mammals as their rich avifauna would be very vulnerable to predation from cats and rats. Until the middle of this century it was understandable practice for natural resources to be fully exploited on the main island, in the interests of human survival; but, by then the results of this over utilisation had become serious and some indigenous species had been exterminated or nearly so. This was recognised and the first Protection Ordinance was passed in 1950, with several subsequent additions as needs have arisen.

In March 1994 the Island Council agreed that Inaccessible Island should be declared as a nature reserve. It is globally important for its many endemic terrestrial species, including the world's smallest flightless bird, the Inaccessible Island Rail. It is also significant as a breeding site for at least 16 seabird species including the northernmost population of Wandering Albatross of a subspecies the centre of whose breeding population is Gough Island. Tristan islanders will retain the right to collect driftwood and guano from this uninhabited island, but other access will be restricted and all living resources will be protected. Taken together with Gough Island, which was already a reserve, some 44% of the land area of Tristan is now set aside for conservation - surely among the highest proportions conserved by any country.

The UK Government submitted a nomination to UNESCO to include Gough on the World Heritage List in October 1994. Justification for such listing included the fact that Gough is the largest scarcely modified cool temperate island ecosystem in the South Atlantic Ocean; it supports huge fur seal populations, two species of endemic landbirds and a range of endemic plants and invertebrates; and is one of the most important seabird colonies of the world. With around 150,000 pairs of Rockhopper Penguins, the island holds about half the world population of the northern race of the species. Gough was granted World Heritage status in December 1995, only the third natural British site to be so honoured.

ENVIRONMENTAL CONCERNS

The group's isolation does not prevent the risk of over-exploitation and this persists in the case of fishing and livestock grazing. But the islanders are now acutely aware of these dangers and appropriate steps are being taken. It is important to the island economy that controlled harvesting of natural resources be allowed to continue however, and active conservation in other instances as of Phylica arborea, has proved successful. This tree provides an important habitat and seasonal source of food for the endemic race of Grosbeak Bunting. Alien species, such as rats, are an ever present threat and the incursion of others like New Zealand Flax (once used for thatching) give cause for concern. Appropriate control and limitation measures are used; but there is a need for continuous action, not always easy to carry out due to the physical nature of the ground.

It has become evident that such interesting islands will become targets for tourism in a shrinking world. This might bring extra revenue to Tristan da Cunha, but the dangers and difficulties may well limit such development. Apart from the sheer isolation, the unpredictability of the weather will always make landing uncertain anywhere other than at the Settlement of Edinburgh. The steep and hazardous terrain, with cliffs up to 600m, will deter all but specialists. The general vulnerability of the habitats, accessible at few points only, is understandably taken into account in the conservation legislation. So, paradoxically, isolation may well prove to be one of Tristan's most valuable assets, by keeping a check on tourism.

The value of isolation has been recognised of late in another context - that of monitoring global changes which can be done best where there is least interference. It was noticed in the early 1980's that non-biodegradable rubbish washed up on the beaches was increasing in quantity at an alarming rate, and that this could be measured and was related to a global trend. Since then, other parameters have been measured at Tristan e.g. mercury levels in seabirds and fish, sea level and temperature changes, and underwater pressure variation. Some of these are now measured continuously there and relayed by satellite to centres in Britain. The list will be extended to include wildlife population monitoring and, already, a Department of Natural Resources has been opened. As a result, this group of British islands may take on a key role in the future.

Apart from everything else however, Tristan da Cunha holds a kind of fascination for all who have been privileged to go there, and for many others who only dream of isolated far-off places.