Blue whales have a worldwide distribution and can be found in all the world's oceans. They travel extensively, feeding heavily in cool waters and migrating to warm waters to breed and give birth.
Blue whales were all but eliminated from the Southern Hemisphere during the days of unrestricted hunting, but, as of 2014, they can be found in every ocean, although in much smaller numbers. Areas near former hunting grounds, such as off the coast of Japan, remain devoid of whales. Populations today tend to either be stable or, in the case of whales found off Iceland and northern California, slowly increasing. The Indian Ocean is home to a subspecies known as the pygmy blue whale.