Sea Lion Island is 7.8 km (4.8 mi) long from east to west and 2.3 km (1.4 mi) wide, with 30 m (98 ft) cliffs at the south-western point and sandy bays to the east. The highest point at 46 m (151 ft) is Bull Hill. East Loafers is the name of the bay on the southern shore. It also has a few ponds, including Beaver and Long Pond. Just to the south is Rum Island, a small seal colony. Other small members of the group are Brandy and Whisky Islands. The geology is mainly sandstone and mudstone, from about 250 million years ago. Some minor fossils have been found.
Sea Lion Island is the southernmost inhabited island of the Falkland Islands. Only formerly inhabited Beauchene Island is located further south. Sea Lion Island Settlement is the southernmost settlement of the Falkland Islands. The island has two airstrips. Historically, Sea Lion Island was a sheep farm and a base for slaughtering penguins to render for oil. When the British ship Viscount was wrecked in 1892, the wreckage was used to build the farmhouse.
The island was managed as a sheep farm for almost all of the 20th century, but in 1997 all but a small flock of sheep was removed. In 1990, the Clifton family who owned the island, sold it to the Falkland Islands Development Corporation (FIDC). They had planted 60,000 stands of tussac grass.
Since then, ecotourism has been the only economic activity. In 1986 FIDC constructed the Sea Lion Lodge, with accommodation for 20 guests. It was prefabricated and flown in kit form to the island by Royal Air Force helicopters and has proved to be a success. It is used by tourists and, since 1996, scientific researchers.
There is a memorial to HMS Sheffield on Bull Hill in the south of the island.
Some 56 species of flowering plants have been recorded, including the Fuegian violet which, in the Falklands, is found nowhere else. The island is known for its marine mammals, including breeding colonies of southern sea lions and southern elephant seals, for which the other islands in the group are haul-out sites. Killer whales occur offshore. Earthwatch has been tracking the habits of elephant seals at Sea Lion Island for years.
The Sea Lion Islands Group has been identified by BirdLife International as an Important Bird Area. It is a significant breeding site for a variety of seabirds and other waterbirds including Falkland steamer ducks, ruddy-headed geese, gentoo penguins (2800 pairs), southern rockhopper penguins (480 pairs), Magellanic penguins, southern giant-petrels (25 pairs) and sooty shearwaters. It also supports populations of striated caracaras (10 pairs), blackish cinclodes, Cobb's wrens and white-bridled finches.