BLUE WHALE

also called Sulfur-bottom, or Sulfur-bottom Whale (Balaenoptera, or Sibbaldus, musculus), mottled, blue-gray baleen whale, belonging to the family Balaenopteridae; the name sulfur-bottom comes from the colour of the yellowish diatoms (algae) found on the bodies of some individuals. The largest of all known animals, the blue whale attains a maximum length and weight of about 30 metres (100 feet) and 150 tons; the largest known individual, a female 33.58 metres (110.14 feet) in length, was reported in 1922. It has a small dorsal fin near its tail, and 80 to 100 long grooves running lengthwise on its throat and chest. It also has short, black baleen, or whalebone, numerous horny fringed plates on the sides of the upper jaw that act as a sieve, removing plankton, on which the animal feeds, from water expelled from its mouth. The blue whale is found alone or in small groups in all oceans. It spends the summer in polar waters, feeding on shrimplike crustaceans (krill), and in winter moves toward the Equator to breed. Once the most important of the commercially hunted baleen whales, the blue whale was greatly reduced in numbers during the late 19th and the first half of the 20th century. It is now protected but is listed as critically endangered in the Red Data Book.