Blue Whale

Balaenoptera musculus

Description

The blue whale is the largest mammal that has ever inhabited the earth. It attains a mature length of 70-85 ft (21-26 m) and has been recorded as long as 106 ft (32 m). The weight can range from 90-150 tons (81-136 metric tons). It has a U-shaped snout and 80-100 throat furrows. The dorsal fin is small and set far back on its streamlined body. Like other baleen whales, it has no teeth and strains its food through a series of plates set within the palate, called the baleen. Its throat is only a few inches in diameter, so that it can ingest nothing larger than small fish. Coloring is slate-blue above and yellowish or whitish below. The female is larger than the male.

Behavior

The blue whale is a powerful swimmer and feeds mainly on schools of krill, a small shrimplike invertebrate, which it scoops up in large quantities— as much as 2 tons (1.8 metric tons) at one feeding. Most blue whales migrate to the krill-rich waters of the polar oceans in summer and return to the middle southern latitudes for breeding in winter. The gestation period is 11 months, after which a single calf is born. The calf weighs as much as 3 tons (2.7 metric tons) at birth and grows at a rate of 200 lbs (90.7 kg) per day. Calves nurse for eight months. One offspring is produced in a two-year period. The life span of the blue whale is only about 20 years.

Habitat

The pelagic blue whale feeds on krill along the edges of the ice pack in summer and migrates to warmer waters for breeding in winter. Whales generally stay within a single hemisphere, migrating either toward the north or the southern poles. During migration, the blue whale occasionally follows the line of the continental shelf and may be seen offshore.

Distribution

Found throughout the world's oceans, the blue whale population is separated into three major breeding groups: North Pacific, North Atlantic, and Antarctic. Some evidence suggests a separate breeding population in the Indian Ocean. Before commercial whaling technology could successfully take the blue whale, it is estimated that some 225,000 roamed the earth's oceans.

Threats

Research undertaken for the International Whaling Commission (IWC) and published in 1989 suggests that the blue whale is still at great risk, despite a moratorium on commercial hunting that had been in effect since 1965. A ten-year systematic survey of feeding grounds used by the Antarctic population found only 453 blue whales in a region where scientists had expected to discover much larger numbers. If these figures are borne out by further research, estimates of the total blue whale population would be slashed by a factor of ten. Instead of there being more than 10,000 blue whales, as was previously thought, fewer than 1,000 may survive. The slow recovery of the blue whale may be due to the difficulties of finding mates at such a small population density, as well as damage caused to the social system of the species by decades of excessive hunting.

Conservation and Recovery

The blue whale is protected by international treaty administered by the IWC. A complete moratorium on hunting the blue whale has been in effect since 1966 and is observed by all 38 countries that are members of the IWC. The ban led scientists to believe that the species was beginning to recover. This new research, however, suggests that this slow-breeding species is not as resilient as scientists hoped. Further research will attempt to determine the population trend.

Contact

National Marine Fisheries Service
Office of Protected Resources
1315 East-West Highway, 13th Floor
Silver Spring, Maryland 20910

References

Baker, M. L. 1987. Whales, Dolphins, and Porpoises of the World. Doubleday, Garden City.

Carrighar, S. 1975. The Twilight Seas: A Blue Whale's Journey. Weybright and Talley, New York.

Evans, P. G. 1987. The Natural History of Whales and Dolphins. Facts on File Publications, New York.

Stevens, W. K. 20 June 1989. "New Survey Raises Concerns about Recovery of Blue Whale." New York Times.

blue whale Baleen whale, related to the rorquals. The blue whale is the largest animal that has ever lived, reaching up to 30m (100ft) in length and weighing as much as 120 tonnes. In summer it lives in polar seas. Mating occurs at the end of winter and the whales migrate to warmer latitudes to give birth. A single calf is born every two or three years, after a 10–11 month gestation period. They live up to 50 years. Overhunting has led to threat of extinction. Species Balaenoptera musculus.

http://www.wdcs.org

blue whale • n. a migratory, mottled bluish-gray rorqual (Balaenoptera musculus), found in all oceans of the world. Known to grow as long as 110 feet (33 m) and weigh as much as 150 tons (136,000 kg), it is the largest animal ever to inhabit the earth.

blue whale (Sibbalds's rorqual, Balaenoptera musculus) See BALAENOPTERIDAE.