Both toothed whales and baleen whales are common in the Southern Ocean. Whales in the first group have teeth and feed on fish and squid, whereas baleen whales filter seawater through fibrous baleen plates to retain plankton and small fish. The whales use the Southern Ocean as feeding grounds during Austral summer and migrate to warmer waters during winter for reproduction.
In late summer when IMR do their monitoring around the South Orkneys, baleen whales are most commonly observed, in particular fin whales, but also humpback and minke whales. In this region they usually find excellent conditions for feeding with high concentrations of krill.
Seals are also naturally divided in two groups, the true seals and eared seals. Unlike the true seals with only an aperture leading to an internal ear, the eared seals have a small external ear. Six species of seals are found in Antarctic waters. Varying among species they feed on fish, squid and krill, whereas the leopard seal (Hydrurga leptonyx) feeds on penguins and other seals. Four of the species are adapted to the ice and breed there, they include the leopard, Ross (Ommatophoca rossii), Weddell (Leptonychotes weddellii) and Crabeater seals (Lobodon carcinophagus). The Antarctic fur seal (Arctocephalus gazella) and elephant seal (Mirounga leonina) breed on beaches, and these are the species typically found during the IMR monitoring around the South Orkneys.