The subantarctic Prince Edward Island group, consisting of Marion Island (46°54’S 37°45’E; 290 km²; max. elevation 1,230 m) and Prince Edward Island (46°37’S 37°57’E; 44 km²; 672 m), lies in the southern Indian Ocean, c.2,300 km south-east of Cape Town and 250 km north of the Antarctic Polar Front. The islands are surrounded by steep coastal cliffs, between 5 m and 500 m high, with very few beaches. A large proportion of the islands consist of poorly drained coastal plains and slopes.On Marion, the coastal plain on the northern, eastern and southern portions of the island forms a rim, 4–5 km wide, rising gently from sea-level to the foot of the mountainous interior at about 300 m. The landscape looks barren, lacking trees and shrubs, and lichens, mosses and liverworts are an important component of the tundra-like vegetation. The coastal plains and slopes hold a mosaic of communities, dominated by tussock grassland. Mires and herbfields occur in wet depressions and drainage lines. The central, mountainous portion of Marion Island has a permanent ice-plateau. The islands are subject to a low average temperature with small diurnal and seasonal ranges, high rainfall and a high incidence of gale-force winds.
See Box for key species. Twenty-nine species of bird, 28 of them seabirds, are thought or known to breed at the Prince Edward Islands. Only one other island group in the southern Oceans, the Crozets, holds more species of breeding seabird. The Prince Edward Islands are estimated to support c.2.5 million pairs of breeding seabirds and may support up to 8 million seabirds in total. The islands hold c.15% and 5% of the global populations of Aptenodytes patagonicus and Eudyptes chrysolophus respectively. Numbers of both species are thought to be stable. The islands also support a large proportion of the population of Eudyptes chrysocome. Large numbers of breeding albatrosses occur, including 36% of the breeding population of the globally threatened Diomedea exulans, which was recently split from other ‘Great Albatross’ forms (D. dabbenena, D. gibsoni and D. antipodensis). The islands also hold breeding Diomedea chlororhynchos (this form was recently split to become Thalassarche carteri), 9% of Diomedea (now Thalassarche) chrysostoma and 18% of Phoebetria fusca populations. Extremely large numbers of Pachyptila salvini and Pterodroma petrels breed on the islands, as do small numbers of Pygoscelis papua (1,755 pairs), Pachyptila turtur (100s of pairs), Garrodia nereis (breeding possible, but not proven), Pelecanoides georgicus (100s of pairs) and the endemic subspecies Chionis minor marionensis, which appears to be declining on Marion Island.
Non-bird biodiversity: Elaphoglossum randii, a small fern that grows on black lava-flows, is endemic to the Prince Edward Islands. Several other plant species, such as Ranunculus moseleyi, Polystichum marionense, Poa cookii, Colobanthus kerguelensis and Pringlea antiscorbutica are shared with the Crozet and Kerguelen groups. A high incidence of local and provincial endemism exists amongst the hepatic flora. At least eight species of insect are endemic to the Prince Edward Islands. Increasing populations of the seals Arctocephalus tropicalis and A. gazella occur on the islands, as does a rapidly declining population of Mirounga leonina.
Pressure/threats to key biodiversity
South African sovereignty over these islands was declared on 12 January 1948. Both islands have recently been gazetted as Special Nature Reserves, down to the low-water mark. Prince Edward is arguably the world’s most pristine subantarctic island of significant size and it merits World Heritage Site status.Feral cats Felis catus, which were the greatest threat to several bird species at Marion Island, were eliminated in 1991 after an extremely effective eradication programme. Pelecanoides urinatrix is no longer thought to breed at Marion Island owing to cat predation. Prior to eradication, the cats were major predators of burrowing Pterodroma macroptera, P. mollis and Halobaena caerulea, which have all exhibited an increase in breeding success since cats were eradicated.A recent development of unprecedented concern is the establishment of a longline fishery for Patagonian toothfish Dissostichus eleginoides on the islands’ shelf waters. Certain species of seabird are prone to alighting on the baited hooks, becoming snagged, and drowning during line setting; this source of mortality affects populations of procellariiform seabirds dramatically. Albatrosses and large Procellaria petrels are particularly vulnerable to being caught on longlines. Longline fishing has been implicated as the primary factor responsible for the global decline of Diomedea exulans in the last three decades. The Patagonian toothfish fishery off Marion and Prince Edward is responsible for large catches of Diomedea chrysostoma and Procellaria aequinoctialis, which is of particular concern for the former species, which only breeds biennially. There are suggestions that the numbers of Procellaria aequinoctialis in study colonies on South Georgia have decreased by up to a third in the last 10 years, suggesting detrimental effects from longline fisheries on this population. Furthermore, Procellaria aequinoctialis caught in the South African hake longline fishery may be birds breeding on Marion Island.The use of bird poles to scare birds, night-setting and the correct use of deck lighting are a few of the recommendations by the Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR) which have become almost standard in most of the world’s legal longline fisheries in an attempt to eliminate seabird mortality. A factor that makes the Prince Edward Islands fishery particularly threatening is that CCAMLR regulations are difficult to enforce, and extensive rule-breaching almost certainly occurs. Despite an initial recommendation by the Sea Fisheries Research Institute that only four toothfish permits be issued, an official fleet exceeding this operated in Prince Edward waters during the year that the fishery opened, and a larger illegal, unlicensed, and uncontrolled fleet is poaching in these waters. If the appropriate mitigation measures are not enforced, and access to this area is not controlled through an efficient observer programme and enforcement of legislation, seabird populations on the island are set to plummet.Eudyptes chrysocome filholi, which is under taxonomic revision and may be split from its congeners E. c. chrysocome and E. c. moseleyi, is suffering a considerable decline in parts of its range. The causal factor for the decline is unknown. The threatened population of the seal Mirounga leonina on Marion Island is decreasing at a rate of 4.8% per year. This has important implications for breeding giant petrels Macronectes, which rely on the pupping season as an important food source. Other threats to the islands include oil pollution (there have been two small spills in less than two years), marine pollution from fisheries and other ships, and potential disturbance from tourism. The Department of Environment and Tourism have written and established a management plan that is being rigorously followed. An environmental impact assessment on the potential impacts of tourism has been produced.
BirdLife International (2019) Important Bird Areas factsheet: Prince Edward Islands Special Nature Reserve. Downloaded from
http://www.birdlife.org on 09/12/2019.