The site comprises the whole of Inaccessible Island as described in the ‘General introduction’.
See Box and Table 2 for key species. At least 33 bird taxa are known. Sixteen species of breeding seabirds and four of native landbirds occur. The seabirds include Eudyptes chrysocome moseleyi, Diomedea exulans dabbenena, D. chlororhynchos, Phoebetria fusca, Pterodroma brevirostris, P. mollis, Pachyptila vittata, Procellaria a. conspicillata, Puffinus gravis, P. assimilis, Pelagodroma marina, Fregetta grallaria, Pelecanoides urinatrix, Catharacta antarctica, Sterna vittata and Anous stolidus. It is possible that the three Tristan Island winter breeders, Pterodroma macroptera, P. incerta and Procellaria cinerea, also breed here.Procellaria aequinoctialis conspicillata is entirely restricted to Inaccessible Island when breeding; estimates in 1999 put the population as between 2,500–10,000 individuals and declining.The terrestrial species include Atlantisia rogersi, Nesocichla eremita gordoni (850 pairs, 1990 estimate) Nesospiza acunhae acunhae (2,500 pairs, 1983 estimate) and N. wilkinsi dunnei (200 pairs, 1983 estimate).Non-breeding visitors include Diomedea melanophris, Macronectes giganteus, M. halli, Fulmarus glacialoides, Daption capense, Pachyptila desolata, Puffinus griseus, Oceanites oceanicus, Porphyrula martinica, Calidris fuscicollis, Larus dominicanus, Sterna paradisaea and Hirundo rustica.
Non-bird biodiversity: The only breeding native mammal is Arctocephalus tropicalis. At least 39 species of native terrestrial invertebrates are known. The island is particularly rich in the listroderine weevils, endemic to the Tristan group as a whole.
Pressure/threats to key biodiversity
The island, including the surrounding waters up to 12 nautical miles, was declared a Nature Reserve in 1997. Perhaps its greatest value is its virtually unspoilt state. The greatest and most immediate threats are the introduction of alien predators, most notably rats, and the accidental firing of the tussock.