The Southern Ocean encircling Antarctica is the world’s largest feeding ground for baleen whales – species like humpbacks that filter tiny organisms from seawater for food. In the 20th century, whalers killed roughly 2 million large whales in the Southern Ocean. Some populations, like the Antarctic blue whale, were reduced by more than 99% and have been struggling to recover, even though most nations ended commercial whaling in the mid-1980s.