blue whale, a baleen whale, Balaenoptera musculus. Also called the sulphur-bottom whale and Sibbald's rorqual, it is the largest animal that has ever lived. Blue whales have been known to reach a length of 100 ft (30.5 m) and to weigh as much as 120 tons; average length is about 75 ft (23 m). The blue whale is slate blue in color and has a dorsal fin. It is toothless and has fringed baleen, or whalebone, plates in its mouth, which act as a food strainer. As water is expelled from the whale's mouth, plankton is trapped behind the strainer. The neck of the blue whale has 80 to 100 conspicuous furrows called ventral grooves, which alternately expand and contract as the animal takes in and expels water. The blue whale is cosmopolitan in distribution. In summer it inhabits polar seas, feeding in the water of melting icepacks; in winter it migrates to warmer latitudes, occasionally reaching the equator. Mating occurs at the end of winter, with a single calf born every second or third year, after a gestation period of 10 to 11 months. The calf is nursed for 6 months and reaches puberty in about 3 years. Blue whales may live 100 years or more. Because of extensive whaling, their numbers have been reduced from an estimated 400,000 to about 12,000, and they are listed as endangered. They are classified in the phylum Chordata, subphylum Vertebrata, class Mammalia, order Cetacea, family Balaenopteridae.
See G. C. Small, The Blue Whale (1971).
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