Mammals

There are only three species of seal that breed on the Island, although solitary vagrants of other species are sometimes seen, and of course the surrounding ocean is rich in whales and dolphins. See the history page for more information on sealing activities in the past. No sealing currently takes place on Marion Island - at least not the terminal kind.

Southern Elephant Seal

Mirounga leonina

Southern elephant seals are found throughout the Southern Ocean with major breeding populations found close to the Antarctic Polar Front - the Marion Island population consists of about 1 200 adults. It is the largest of the seals: a fully grown adult male can weigh up to 4.5 tons, compared to 400-600kg for females. Seals can reach 20-23 years of age, although the males only begin breeding at age 8, and the females around age 6. Their diet consists of about 75% squid and 25% fish. They spend between 8 and 10 months a year at sea, only coming on land to breed and moult. The breeding season starts in mid-August when males start hauling out and competing for dominance on beaches. The pregnant females join them from the beginning of September until mid-October, giving birth approximately a week after they haul out. The pups are weaned 3 weeks later, and the female leaves the harem soon after. The males return to sea in mid-November after having fasted since the beginning of the breeding season. Moulting is the second annual event that ties elephant seals to the Island as they have to remain on land for 30-40 days while they shed skin and hair in great patches. Males, females and immature seals moult at different times of the year, starting in November and lasting until April. Elephant seals return to their island of birth to breed and moult, but the rest of the year they range widely, often visiting the continents adjoining the Southern Ocean, the pack-ice region and the Antarctic continent. They make biannual, round trip migrations lasting 2 to 8 months and covering 2 000-7 500km, during which they dive continuously. Dives of up to 1 452m, lasting up to 113 minutes, have been recorded for adult males.

Sub-Antarctic Fur Seal & Antarctic Fur Seal

Arctocephalus tropicalis & Arctocephalus gazella

The two fur seals found on Marion Island are similar in appearance (especially the females and pups), but the males can be told apart by the black crest and ginger-brown belly of the Sub-Antarctic compared to the more uniform grey-brown of the Antarctic Fur seal. They also favour different breeding sites, although some hybridization occurs in mixed colonies. Breeding sites of the Sub-Antarctic Fur seals are mainly confined to the exposed west side of the island, while breeders of the smaller Antarctic fur seal population are found on the southern coast. Their adult population sizes were approximated at 49 000 and 1 200 seals respectively in 1994/95. Both species show similar haul-out patterns, with breeding starting in September/October and lasting until the pups are weaned in April, and moulting occurring from February to April. The Antarctic Fur seal feeds mainly on fish, squid and crustaceans, while the Sub-Antarctic Fur seal is a more general feeder and may also prey on penguins.

Vagrants

These include the solitary Leopard Seal (Hydrurga leptonyx) that breeds on pack-ice, the Weddell Seal (Leptonychotes weddellii) which is the most southerly of the Antarctic seals, and the South African (Cape) Fur Seal (Arctocephalus pusillus pusillus) from further north. Leopard seals are seen most years on Marion Island, but there have only been single sightings of the other two species.

Whales and Dolphins

The most frequent visitor is the Killer-Whale (Orcinus orca) which is seen throughout the year although more frequently in summer. Other cetaceans sighted include Pilot Whales (Globicephala melaena edward), Southern Right Whales (Eubalaena australis) and Humpback Whales (Megaptera novaeangliae).

Terrestrial Mammals

Marion Island is home to only one terrestrial mammal, the House Mouse (Mus musculus). It was introduced through shipwrecks and sealers' expeditionsin the 1800s and has since colonised the entire island up to 750masl. Their numbers peak towards the end of summer and drop off in winter when food and shelter become more scarce. They feed mainly on insects (although they create chaos in the food stores of the base and field huts), and are thus a potential threat to the Marion Island ecosystem. Past introductions of mammals include cats, sheep, pigs, goats, donkeys and dogs.