Scientists consider the blue whale to be the largest animal that has ever lived on Earth. An average adult measures 79 to 88 feet (24 to 27 meters) long and weighs between 130 and 150 tons (118 and 136 metric tons). In the past, some blue whales reached a length of 100 feet (30 meters). Now, the animals seldom grow that large because of extensive whaling (the hunting of whales).
The blue whale has a wide, U–shaped head and a dorsal (on its back) fin. Its body is slate blue in color. Sometimes, microorganisms accumulate on the whale’s body, giving it a faintly yellow sheen. This is why it is also called the sulfur–bottomed whale.
The blue whale feeds mainly on krill, which are small, shrimplike shellfish. Like all whales in its family, the blue whale uses the fringed baleen (whalebone) plates that line its mouth to strain krill from seawater.
The animal has 80 to 100 furrows (called ventral grooves) lining its narrow neck. When it sucks in seawater, the grooves allow its throat to expand like a pouch. As it expels the large volume of water from its mouth, its baleen plates trap the krill.
Blue whales mate at the end of winter. After a gestation (pregnancy) period of 300 to 330 days, a female blue whale gives birth to one calf, which measures 20 to 23 feet (6 to 7 meters) long. The calf nurses for up to seven months.
Habitat and current distribution
In winter, they migrate to warmer waters near the equator, where they will mate. Some blue whales, however, do not appear to migrate, residing year–round in tropical coastal areas. Such whales have been observed off the coast of Peru and in the northern Indian Ocean.
Scientists estimate that less than 2,000 blue whales currently exist in the world’s oceans.
History and conservation measures
When large–scale whaling began in the seventeenth century, blue whales were considered too difficult to hunt because of their size, speed, and strength. This view changed in the mid–nineteenth century with the development of the exploding–head harpoon and the factory ship (which could completely process whales caught at sea).
Blue whales were now a prime prey, and their numbers decreased drastically, especially in the twentieth century. Between 1920 and 1970, an estimated 280,000 blue whales were slaughtered.
The blue whale also faces the loss of its main food source, krill. Scientists have discovered that the krill population has decreased by almost 90 percent since 1980. Krill feed on algae that grow underneath sea ice. As temperatures have risen in Antarctica in the last 20 years, melting a sizable portion of sea ice, the algae population has diminished.
In a domino effect, this loss could affect the entire Antarctic food chain. Some scientists believe this situation is the result of global warming—the rise in Earth’s temperature that is attributed to the buildup of carbon dioxide and other pollutants in the atmosphere.