The blue whale is the largest animal to ever live, in the entire history of Earth. Reaching lengths of at least 110 feet (33 meters) and weights of 209 tons (190 tonnes), these animals are only slightly smaller than the United States Space Shuttle. Their incredible size is only possible because of their aquatic lifestyles and the buoyancy provided by seawater. On land, an animal as large as the blue whale would almost certainly be crushed under its own weight.
Interestingly, though they are enormous, blue whales are not predatory. They filter feed for tiny krill and are totally harmless to people (other than through accidental collisions). This life history strategy is common among several large animals in the ocean, including the whale shark, the basking shark, and the other great whales. Like all whales, blue whales are mammals and give live birth to very large calves that they nurse for six or seven months. Because the female is responsible for providing milk for its babies, she must store extra energy reserves and is consequentially larger than males. All of the record blue whales (by size) are females. Males do not provide parental care and do not seem to live near the females/young for most of the year.
Blue whales have a truly global distribution and live in every ocean except the parts of the Arctic that remain covered with ice throughout most of the year (including summer). There are three distinct populations of blue whales (North Atlantic, North Pacific, and southern hemisphere), and individuals are known to undergo very long migrations between feeding grounds near the poles and calving grounds in the tropics. Their very large size may help blue whales (and other migrating animals) survive such long trips through waters that may provide relatively little food.
Unfortunately, blue whales were one of the hardest hit species by commercial whaling, and they have been slow to recover since their worldwide protection in 1966. Experts continue to view them as endangered (highly vulnerable to extinction) and estimate their numbers to be only three to ten percent of what they were before whaling. Today, a primary threat to blue whale recovery is accidental interactions with fishing gear and with ships, but their numbers are slowly increasing. To compound their trouble, however, blue whales’ preferred food source – krill – is now fished commercially. Their recovery from commercial whaling is in direct competition with commercial fishers in the Southern Ocean. As that fishery takes more and more krill, the slow increase in numbers of blue whales may stop or even be reversed.