Cunha Group Research Articles

Important marine areas for the conservation of northern rockhopper penguins within the Tristan da Cunha Exclusive Economic Zone

The designation of Marine Protected Areas has become an important approach to conserving marine ecosystems that relies on robust information on the spatial distribution of biodiversity. We used GPS tracking data to identify marine Important Bird and Biodiversity Areas (IBAs) for the Endangered northern rockhopper penguin Eudyptes moseleyi within the Exclusive Economic Zone (EEZ) of Tristan da Cunha in the South Atlantic. Penguins were tracked throughout their breeding season from 3 of the 4 main islands in the Tristan da Cunha group. Foraging trips remained largely within the EEZ, with the exception of those from Gough Island during the incubation stage. We found substantial variability in trip duration and foraging range among breeding stages and islands, consistent use of areas among years and spatial segregation of the areas used by neighbouring islands. For colonies with no or insufficient tracking data, we defined marine IBAs based on the mean maximum foraging range and merged the areas identified to propose IBAs around the Tristan da Cunha archipelago and Gough Island. The 2 proposed marine IBAs encompass 2% of Tristan da Cunha’s EEZ, and are used by all northern rockhopper penguins breeding in the Tristan da Cunha group, representing ~90% of the global population. Currently, one of the main threats to northern rockhopper penguins within the Tristan da Cunha EEZ is marine pollution from shipping, and the risk of this would be reduced by declaring waters within 50 nautical miles of the coast as ‘areas to be avoided’.

A second documented record of Spectacled Petrel Procellaria conspicillata in Argentine waters

The Spectacled Petrel Procellaria conspicillata is endemic to Inaccessible Island, in the Tristan da Cunha group (central South Atlantic). The species is considered an occasional visitor to Argentina and there are few records of the species in national waters. On 13 February 2014, two birds were observed (and photographed) 89 nautical miles southeast off Buenos Aires Province at 38°55'S, 56°00'W. This record represents the second documented record of Spectacled Petrel for Argentina.

Hydroids (Cnidaria: Hydrozoa) from Tristan da Cunha and St. Helena

The present report provides the first account of the shallow water hydroids of St. Helena, which comprises 17 species, and adds nine new records to the hydrozoan fauna of the Tristan da Cunha group of islands, raising their number to 34. A total of 34 species, belonging to five families of Anthoathecata and eight families of Thecata, are discussed herein. Although distributional data are given for each species, brief diagnoses are provided for the lesser known or unidentifiable species, and the common taxa are occasionally accompanied by succinct remarks. Illustrations are provided for nearly all species in order to justify their identification and to facilitate identification by others.Fiordlandia protectaandFilellum bouvetensis,both from Gough Island, represent the second world records and extend their known area of distribution.

A Brick for the Cathedral of BryogeographyThe Liverworts and Hornworts of the Tristan da Cunha Group of Islands in the South Atlantic Ocean

A Brick for the Cathedral of BryogeographyThe Liverworts and Hornworts of the Tristan da Cunha Group of Islands in the South Atlantic Ocean

Mottled Petrel Pterodroma inexpectata in the Drake Passage, South Atlantic, March 2008

The ‘Atlantic Odyssey’ is the annual reposi- tioning trip of the Professor Molchanov, a small Expedition Cruise ship that spends the austral summer in Antarctic waters and the northern summer in the Arctic. For enthusiasts of seabirds, cetaceans, islands, and photography, the voyage from Ushuaia in Argentina south to the Antarctic Peninsula, and thence north to Cape Verde via South Georgia, the Tristan da Cunha group, St Helena, and Ascension Island provides a superb opportunity to view marine life across 70 degrees of latitude. On the morning of 11 March 2008, we were heading south on our second day in the Drake Passage, with a moderate northwest wind, two-metre swell, high thin overcast skies, and excellent visibility. At 11.20 hours (ship’s time, position 60o17’S 69o44’W) we were observing from the sun deck above the bridge when a medium-sized petrel flew close across the bow from east to west. Similar sized seabirds seen that morning were Cape Petrel Daption capense, Antarctic Prion Pachyptila desolata, Thin-billed Prion P. belcheri, and Soft- plumaged Petrel Pterodroma mollis.

Seismic Activity Associated with a Probable Submarine Eruption near Tristan da Cunha, July 2004-July 2006

Research Article| May 01, 2007 Seismic Activity Associated with a Probable Submarine Eruption near Tristan da Cunha, July 2004–July 2006 Aoife O'Mongain; Aoife O'Mongain British Geological Survey Murchison House, West Mains Road Edinburgh, EH9 3LA, United Kingdom bbap@bgs.ac.uk (B.B.) Search for other works by this author on: GSW Google Scholar Lars Ottemoller; Lars Ottemoller British Geological Survey Murchison House, West Mains Road Edinburgh, EH9 3LA, United Kingdom bbap@bgs.ac.uk (B.B.) Search for other works by this author on: GSW Google Scholar Brian Baptie; Brian Baptie British Geological Survey Murchison House, West Mains Road Edinburgh, EH9 3LA, United Kingdom bbap@bgs.ac.uk (B.B.) Search for other works by this author on: GSW Google Scholar David Galloway; David Galloway British Geological Survey Murchison House, West Mains Road Edinburgh, EH9 3LA, United Kingdom bbap@bgs.ac.uk (B.B.) Search for other works by this author on: GSW Google Scholar David Booth David Booth British Geological Survey Murchison House, West Mains Road Edinburgh, EH9 3LA, United Kingdom bbap@bgs.ac.uk (B.B.) Search for other works by this author on: GSW Google Scholar Author and Article Information Aoife O'Mongain British Geological Survey Murchison House, West Mains Road Edinburgh, EH9 3LA, United Kingdom bbap@bgs.ac.uk (B.B.) Lars Ottemoller British Geological Survey Murchison House, West Mains Road Edinburgh, EH9 3LA, United Kingdom bbap@bgs.ac.uk (B.B.) Brian Baptie British Geological Survey Murchison House, West Mains Road Edinburgh, EH9 3LA, United Kingdom bbap@bgs.ac.uk (B.B.) David Galloway British Geological Survey Murchison House, West Mains Road Edinburgh, EH9 3LA, United Kingdom bbap@bgs.ac.uk (B.B.) David Booth British Geological Survey Murchison House, West Mains Road Edinburgh, EH9 3LA, United Kingdom bbap@bgs.ac.uk (B.B.) Publisher: Seismological Society of America First Online: 09 Mar 2017 Online ISSN: 1938-2057 Print ISSN: 0895-0695 © 2007 by the Seismological Society of America Seismological Research Letters (2007) 78 (3): 375–382. https://doi.org/10.1785/gssrl.78.3.375 Article history First Online: 09 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Aoife O'Mongain, Lars Ottemoller, Brian Baptie, David Galloway, David Booth; Seismic Activity Associated with a Probable Submarine Eruption near Tristan da Cunha, July 2004–July 2006. Seismological Research Letters 2007;; 78 (3): 375–382. doi: https://doi.org/10.1785/gssrl.78.3.375 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietySeismological Research Letters Search Advanced Search The remote South Atlantic island of Tristan da Cunha (hereafter abbreviated to “Tristan”) is a large oceanic shield volcano rising more than 5,500 m from the sea floor to an altitude of 2,060 m above sea level. Tristan along with the islands Inaccessible and Nightingale and a number of smaller islets forms the Tristan da Cunha group (figure 1), which lies on a submarine plateau approximately 200 km east of the Mid-Atlantic Ridge near its junction with the Walvis Ridge (Morgan 1971; Fairhead and Wilson 2005). The group is believed to represent the surface volcanic... You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Additions to the ichthyofauna of the Tristan da Cunha Group, South Atlantic Ocean

Specimens of two, possibly three, rare species of fishes were collected at the Tristan da Cunha Group toward the end of a 2004 South Atlantic cruise (ICEFISH). The dragonet Synchiropus valdiviae (Trunov, 1981), was previously known from only two adult males taken on Walvis Ridge. We collected two adult females and three juveniles, which are described here. The pearlfish Echiodon atopus Anderson, 2005, was recently described from a specimen collected north of Inaccessible Island. It differs from congeners in its high precaudal vertebral count, equivalent dorsal and anal rays anterior to vertebra 31 and other features of the axial skeleton and fins. Lastly, an unusual specimen of the rockfish genus Sebastes taken in a commercial lobster pot represents either a previously unreported variant of S. capensis or an undescribed species. It differs from the typical South Atlantic S. capensis in its coloration and lack of supraocular spines.

Description of a new species of Echiodon (Teleostei: Carapidae) from the South Atlantic Ocean

A new species of pearlfish, Echiodon atopus, is described from a single adult male, 176 mm TL, collected off Inaccessible Island, Tristan da Cunha Group, South Atlantic Ocean. It is characterized by its high, equal D 30 and A 30 counts (46 rays each), 7 anal rays anterior to the dorsal-fin origin, 38 precaudal vertebrae, 18 pectoral-fin rays and ventral swim bladder tunic ridges. It was caught in a bottom trawl over a deep lava-reef structure, but may be pelagic.

Breeding biology of the Atlantic Petrel, Pterodroma incerta, and a population estimate of this and other burrowing petrels on Gough Island, South Atlantic Ocean

The Atlantic Petrel, Pterodroma incerta, endemic to the Tristan da Cunha group in the South Atlantic and globally threatened, is one of the least known of the world's seabirds. At Gough Island, Atlantic Petrels are winter breeders, with single eggs laid in June—July and chicks fledging in December. Birds were exclusively nocturnal on land. The pre-egg exodus of ∼50 days and nestling period of almost 140 days are near the longest recorded for Pterodroma species, and support the general pattern of prolonged development found in winter-breeding Procellariiformes. Chicks grew at a very slow rate, suggesting poor at-sea feeding conditions. Breeding success averaged only 20% and introduced House Mice, Mus musculus, were probably responsible for considerable losses of chicks in two breeding seasons. Preliminary population modelling predicts a decline in numbers. The potential impact of introduced mice suggests that the species’ conservation status be upgraded from Vulnerable to Endangered and that further research on this issue is a high priority. The first quantitative estimate of breeding numbers indicates a population of ∼1.8 million pairs of Atlantic Petrels. Provisional population estimates of Great Shearwaters, Puffinus gravis (980000 pairs), Soft-plumaged Petrels, Pterodroma mollis (400000 pairs), and Broad-billed Prions, Pachyptila vittata (1750000 pairs) confirm the international significance of Gough Island as a site for breeding seabirds.

Demography and conservation of the Tristan albatross Diomedea [exulans] dabbenena

The Tristan albatross Diomedea [exulans] dabbenena is the third rarest albatross species, with a breeding population of around 1500 pairs almost totally restricted to Gough Island in the Tristan da Cunha group, central South Atlantic. During January 2000, the entire breeding population of Gough was surveyed for the first time since 1956, and 2400 incubating pairs were counted. An analysis of the areas that are likely to have been surveyed most accurately in the past suggests that the population has decreased by around 28% over 46 years. The number of large chicks counted over three successive seasons (1999–2001) was highly variable (range 318–1129). The average count over this period (705 chicks) is less than counts made in 1979 (792) and 1982 (798). A total of 656 chicks were counted in September 2001, giving an island breeding success of just 27.3%. However, breeding success varied considerably in different areas of the island, ranging from 17.6 to 68.0%. During the 2001 season most breeding failures were of large chicks, and over 4 years where data were available, 75% of breeding failures occurred during the chick period. Predation by introduced house mice Mus musculus is the most likely cause of chick mortality. In a small study population, birds began breeding at an average age of 9.7 years and annual adult survival from 1985 to 2001 was 92.6% (SE=1.6%). Both breeding success and adult survival estimates are low in comparison with other Diomedea species and population modelling predicts a population decreasing at an annual rate of 2.9–5.3%. Further research is needed urgently to assess whether breeding success is typical, and to confirm that mouse predation is the cause of chick mortality. The low productivity of this species will compound the negative impacts of longline fishing mortality, which are likely to be reducing adult and juvenile survival.

The Importance of Tracking Introduced Species: New Records of Athetine Rove Beetles from South Atlantic Inaccessible Island (Coleoptera, Staphylinidae, Aleocharinae)

Two species of athetine rove beetles are recorded from Inaccessible Island, in the Tristan da Cunha group of islands in the South Atlantic for the first time. One species, Halobrecta flavipes Thomson, represents a new introduction possibly from the Palearctic region, and the other species, Atheta (Xenota) pseudoinsulana Klimaszewski, new species, is of an undetermined origin. The latter belongs to the Laticollis group of species that are broadly distributed and are known to occur in the Palearctic, Nearctic, Afrotropical, and Oriental regions as well as some Atlantic Islands. The lectotype is designated for Homalota dilutipennis Motschulsky [= Atheta dilutipennis (Motschulsky)].

Population status, breeding biology and conservation of the Tristan Albatross Diomedea [exulans] dabbenena

Tristan Albatross Diomedea [exulans] dabbenena is the most genetically distinct of the five taxa that form the Wan dering Albatross superspecies, and has been listed as Endangered. It breeds only on Gough and Inaccessible Islands in the Tristan da Cunha group, central South Atlantic Ocean. The entire breeding population was surveyed during 1999-2000. A mid-September survey at Gough Island recorded 1,129 chicks, equivalent to an annual breeding effort by approximately 1,500 pairs. Only one chick was present at Inaccessible Island in 1999, and another pair laid an egg in 2000. The annual breeding effort at this island has not exceeded three pairs since the 1950s. None were found during an incomplete survey at Tristan, where the species bred in the past, but birds were seen flying over the island. A complete survey and attempts to promote recolonization of Tristan are warranted. Breeding success at Gough Island averaged 63%, and no birds that bred successfully attempted to breed the following year. Breeding success was greater and less variable in a large colony at Gonydale than at a peripheral colony at Tafelkop. Young birds returned to the island after 3-4 years (4-5 years old), and the modal age of first breeding was 8 years, with some individuals breeding as young as 6 years. Most chicks (81%) recruited to their natal colony, but some recruited to colonies up to 3 km from their natal site. Among adults, fidelity to partners and breeding colony was high. Of nine birds recovered away from the island, at least four were killed by longline fishing. Despite its known mortality on longlines, the Gough Island census exceeded demipopulation estimates from the 1970s and early 1980s, possibly due to incomplete coverage by previous surveys and a poor breeding season in 1998. Given the lack of evidence for a population decrease, Tristan Albatross should be listed as Vulnerable. It is the third rarest albatross species, however, and its population size warrants monitoring. We provide guidelines for repeatable censuses at Gough Island.

Geochemistry of inaccessible island volcanics

Inaccessible Island, part of the Tristan da Cunha group, is older than Tristan itself but younger than Nightingale. It comprises an alkali basalt-trachybasalt-phonolitic trachyte series which is similar to but less alkaline than that of Tristan. Chemical and isotopic analyses for a new suite of sixteen samples are presented. SrNdPb isotopes and incompatible element ratios exhibit a DUPAL signature ( 87 Sr 86 Sr = 0.7050 , 143 Nd 144 Nd = 0.51255 ), underlining the similarity to Tristan. Most of the Inaccessible lavas appear to have been derived by melting of an enriched mantle source. However, one small group of rocks from the island is isotopically distinct and shows progressive uranium depletion with increasing 143 Nd 144 Nd (0.51262–0.51267) and decreasing 87 Sr 86 Sr (0.70454–0.70414). Admixture of a component from a Mid-Ocean Ridge basalt (DMM) source can explain this anomalous group and minor Pb isotope variations appear to support this explanation. These distinct lavas are not confined to any particular stratigraphic level, implying the availability of both sources throughout the growth of the island. The isotopic variability found for Inaccessible is distinct from that on Tristan and from the Walvis Ridge basalts.

Reproductive dynamics of twoJasusspecies in the South Atlantic region

Comparisons of egg size, brood size and egg production per lifetime (fecundity per recruit) between Jasus tristani from the Tristan da Cunha group of islands and J. lalandii from the west coast of southern Africa reveal distinct differences. Females of the continental species J. lalandii have smaller eggs, larger brood sizes and a greater fecundity per recruit than the insular species J. tristani. Greater egg production in J. lalandii implies that rates of larval mortality are likely to be higher in this species. A number of possible reasons may be involved — these include differential predation rates on newly hatched and returning larval forms, as well as losses induced by topographic forcing of currents by the Walvis Ridge.

Pollen analysis of a Quaternary peat sequence on Gough Island, South Atlantic.

A peat sequence on Gough Island, South Atlantic, is described. The deposit is at least 43 000 years old, and may be early Quaternary in age. Pollen analyses suggest a flora and vegetation on Cough Island similar to those of today, supporting conclusions based on pre-Holocene pollen samples from islands in the Tristan da Cunha group. The present flora has probably been on Cough Island continuously for at least the last 40000 years, and is not a Holocene immigrant flora.

The rat problem on oceanic islands—research is needed

In October 1983 a rat was reported to have been seen on Gough Island, an outlier of the Tristan da Cunha Group in the South Atlantic. Gough Island has no permanently resident human inhabitants, but supports one of the largest and most diverse assemblages of breeding seabirds now remaining anywhere in the temperate zones. The author was a member of a small team of biologists that spent three weeks on Gough Island, in October-November 1984, to try to confirm whether there were any rats on the island, and if so to make recommendations for their control and extermination. The following proposals result from experience in carrying out this survey, and from writing World Conservation Strategy proposals for Oceanic Islands for the IUCN.

THE DENSTONE EXPEDITION TO INACCESSIBLE ISLAND

Inaccessible Island, the second largest in the Tristan da Cunha group, is a volcanic remnant which, owing to its steep cliffs on all sides, remained unmapped and largely unexplored until 1982, when the Denstone Expedition to Inaccessible Island, a party of 16 in all, carried out the first shore-based survey and scientific exploration there. The main party was put ashore from a South African ship and established a base on the only part of the Island from where there is access to the interior. This paper gives a brief description of Inaccessible Island, a summary of the work undertaken in the major disciplines of biology and geology, and includes the resulting map. INACCESSIBLE ISLAND is situated 40 km south west of Tristan da Cunha in the South Atlantic Ocean and is British territory, under the Protectorate of St Helena. It is roughly rhomboidal in shape, approximately 4x5 km in area, of volcanic origin and characterized by steep cliffs on all sides, with narrow beaches. Prior to the Denstone Expedition, there had been only six previous scientific visits, all of short duration and limited, in all but two cases, by failure to gain access to the interior of the Island. Thus, no previous shore-based map of Inaccessible Island existed and both biological and geological collections were limited. No detailed study had been attempted of any endemic species, or of the Island's geomorphology from ashore. The object of the Denstone Expedition was to make good these deficiencies. This was successfully achieved between October 1982 and February 1983 by a team of past and present pupils of Denstone College, Staffordshire,with three Tristan Island guides. Figure 1 is the resulting initial map. Topography The Island is surrounded by near-vertical sea cliffs of between 155 m at East Point and 490 m in the south west. The western part ofthe Island contains the highest ground from where a number of ridges run south-eastwards, forming the major catchment area of three drainage basins emptying immediately south of Joe's Hill. The extreme north-west part of the Island is drained to the north by two streams with outlets over the cliffs at North Point. This area is separated from the north-central and north-eastern parts of the Island by the prominent Long Ridge running north-south. To the east of the ridge lies the third drainage basin containing a stream which flows over the cliffs at the western end of Waterfall Beach. The eastern side of the Island is dominated by Round Hill, a breached parasitic cone. Inland of East Point is a low, flat plateau with no drainage system. The Island is subject to severe weathering and erosion as evidenced by numerous and often large landslides along the cliffs. Blenden Hall is part of a large low-lying area at sea level which would appear to constitute landslide material, possibly instigated during the formation of a large parasitic cone just to the north of the area. On its surface is Skua Bog. Pebble and boulder beaches occur intermittently around the Island, totalling approximately two-thirds of the coastal perimeter, and a well developed storm beach occurs at West Point.

The Denstone Expedition to Inaccessible Island

Inaccessible Island, the second largest in the Tristan da Cunha group, is a volcanic remnant which, owing to its steep cliffs on all sides, remained unmapped and largely unexplored until 1982, when the Denstone Expedition to Inaccessible Island, a party of 16 in all, carried out the first shore-based survey and scientific exploration there. The main party was put ashore from a South African ship and established a base on the only part of the Island from where there is access to the interior. This paper gives a brief description of Inaccessible Island, a summary of the work undertaken in the major disciplines of biology and geology, and includes the resulting map. INACCESSIBLE ISLAND is situated 40 km south west of Tristan da Cunha in the South Atlantic Ocean and is British territory, under the Protectorate of St Helena. It is roughly rhomboidal in shape, approximately 4x5 km in area, of volcanic origin and characterized by steep cliffs on all sides, with narrow beaches. Prior to the Denstone Expedition, there had been only six previous scientific visits, all of short duration and limited, in all but two cases, by failure to gain access to the interior of the Island. Thus, no previous shore-based map of Inaccessible Island existed and both biological and geological collections were limited. No detailed study had been attempted of any endemic species, or of the Island's geomorphology from ashore. The object of the Denstone Expedition was to make good these deficiencies. This was successfully achieved between October 1982 and February 1983 by a team of past and present pupils of Denstone College, Staffordshire,with three Tristan Island guides. Figure 1 is the resulting initial map. Topography The Island is surrounded by near-vertical sea cliffs of between 155 m at East Point and 490 m in the south west. The western part ofthe Island contains the highest ground from where a number of ridges run south-eastwards, forming the major catchment area of three drainage basins emptying immediately south of Joe's Hill. The extreme north-west part of the Island is drained to the north by two streams with outlets over the cliffs at North Point. This area is separated from the north-central and north-eastern parts of the Island by the prominent Long Ridge running north-south. To the east of the ridge lies the third drainage basin containing a stream which flows over the cliffs at the western end of Waterfall Beach. The eastern side of the Island is dominated by Round Hill, a breached parasitic cone. Inland of East Point is a low, flat plateau with no drainage system. The Island is subject to severe weathering and erosion as evidenced by numerous and often large landslides along the cliffs. Blenden Hall is part of a large low-lying area at sea level which would appear to constitute landslide material, possibly instigated during the formation of a large parasitic cone just to the north of the area. On its surface is Skua Bog. Pebble and boulder beaches occur intermittently around the Island, totalling approximately two-thirds of the coastal perimeter, and a well developed storm beach occurs at West Point.

Conservation in the Antarctic

Formidable legal and administrative complexities arise from conflicting claims to jurisdiction and the continued absence of generally recognized sovereignty over much of the region. Existing conservation measures fall into three groups: elaborate laws made by governments claiming Antarctic territories, more restricted laws, and simple instructions for particular expeditions. The Antarctic Treaty, 1959, made it possible to begin coordinating all these separate instruments. No claimed jurisdiction has been surrendered or recognized: each government has started to harmonize its own control measures with the ‘Agreed Measures for the Conservation of Antarctic Fauna and Flora’, 1964. This scheme applied only to land areas and has since been evolving in the light of experience. Although not yet formally approved by all the governments concerned, it is working effectively by voluntary agreement. Different approaches are necessary for conservation of Southern Ocean resources, especially krill. A start has been made with the ‘ Convention for the Conservation of Antarctic Seals’, 1972. There are many outstanding problems: all require effective cooperation between scientific and legal advisers, diplomats and politicians. Mention is made of recent British conservation legislation for South Georgia, the Falkland Islands and the Tristan da Cunha group. Some of the next steps are outlined.

BIOLOGY AND ZOOGEOGRAPHY OF THE VEMA SEAMOUNT: A REPORT ON THE FIRST BIOLOGICAL COLLECTION MADE ON THE SUMMIT

Summary A collection of marine organisms, made in 1964 on the summit region of the volcanic Vema Seamount, situated some 450 miles off the west coast of South Africa, is discussed. The general terrain of the summit was rocky, and kelp, lesser algae and encrusting animals were dominant. The collection consisted of some 22 species of algae and over 105 species of benthic invertebrates. The three largest zoogeographical groups of animals on the Seamount were (a) the endemic species (28%, of which the majority belonged to the little known Porifera and Ascidiacea), (b) the cosmopolitan, and those species with a scattered distribution (27%) and (c) those species found only on the Seamount and in South Africa (25%). Species found on the Seamount whose distribution was limited to the Indo-Pacific region, and to West Africa and Europe with some overlapping into South Africa, amounted each to about 10% of the fauna. Only one species, the rock lobster, Jasus tristani, is confined to the Seamount and the relatively close Tristan da Cunha group of islands.