Ten species of whales are found in Antarctic waters.
Together with the humpback (Megaptera novaeangliae)and the minke (Balaenoptera bonaerensis) they feed predominantly on krill. Krill often form vast swarms or schools in the Southern Ocean. These aggregations can stretch for up to 20 kilometres and can contain over a million tonnes of krill in densities over 10,000 animals in every cubic metre - the largest concentrations of animal life in the world. Baleen whales have evolved special fringed plates of keratin (called baleen) in their mouths that allow them to swallow large mouthfuls of krill from these swarms, and filter out the unnecessary sea water. The sei (Balaenoptera borealis)and the Southern right whales (Eubalaena australis) are also baleen whales but their diet consists of much smaller crustaceans.
Antarctic toothed whales include the killer whale or orca (Orcinus orca), which is the Southern Ocean’s top predator. They hunt in packs and eat penguins, seals, and the young of other whales. The much larger sperm whale (Physeter macrocephalus) is also a toothed whale and feeds on fish and squid at great depth.
Many Southern Ocean whales are migratory, and head to tropical waters during the Antarctic winter. Calves are born in these warmer waters. Every day a newborn blue whale drinks 200 litres of milk that has 9 times the fat content of human milk. This enables a calf to double from its birth size of 2.5 tonnes in just 6 months, enough to take on a migration of thousands of kilometres when the whales return south in the austral spring to feed. A young calf will accompany its mother for several years on the annual migration. Females will not mate again until their calf is independent.
Over 1.3 million whales were taken from Antarctic waters last century. It is estimated that there were over 225,000 blue whales before their exploitation; today there are fewer than 10,000.
Many whale populations are now recovering because they have been protected from hunting since 1986. The recovery of some, like the blue whales, is still uncertain and numbers are still critically low. Others, such as humpbacks, are undergoing a population boom–but their numbers are still below historical levels.