Last modified: Thursday October 12th, 2000

Blue whale

Balaenoptera musculus (Linnaeus, 1758)

Taxonomy

Currently, there are 3 recognized subspecies of blue whales: B. m. intermedia, found in the Southern Hemisphere, B.m. musculus, in the Northern Atlantic and Pacific Oceans, and B .m. brevicauda, from the subantarctic waters of the Indian and Southeast Atlantic Oceans. According to Rice (1998) there is a fourth subspecies, B. m. indica in the Northern Indian Ocean. B. m. brevicauda is also called the pygmy blue whale. Some consider this a separate species: Balaenoptera brevicauda, although this distinction is not generally accepted.

Appearance

The blue whale is the largest animal alive today. The longest specimen was a 33.58 m long female. Blue whales are fundamentally bluish grey in color with white undersides to the flippers. In colder waters, diatoms attached to the skin can give the whale a yellowish color. This gave rise to the alternative common name sulphur-bottom. The head is wide and flat. A single ridge extends from the blowhole to the tip of the rostrum.

The small dorsal fin (about 40 cm high) is positioned far back (at about 75% of the body length, from the rostrum). The ventral surface contains 55-88 longitudinally parallel grooves. The baleen is black and the largest baleen plates are usually not longer than 1 m.

Distribution

Most North Pacific whales move towards the Arctic in spring and summer to feed and spend the winter in subtropical and tropical waters. There is some evidence of a resident population in the Eastern tropical Pacific. In the North Atlantic the whales are found East of Spitsbergen in spring and summer and from the Davis Strait to Greenland. The Atlantic wintering grounds are unknown. In the Southern hemisphere, the feeding grounds are a circumpolar belt around the Antarctic pack ice. Exact locations of the wintering grounds on the Southern hemisphere are unknown.

Population dynamics and life history

Female give birth to a single calf once every 2 to 3 years. The gestation period is probably about 10-11 months. At birth, calves are 6-7 m long. Females become sexually mature at a length of 21-23 m, when they are about 5 years of age (10 years according to other sources). Males become sexually mature at 20-21 m. Not much is known about survival and longevity of blue whales. Maximum age estimates range from 30 to over 80 years.

Population status

The current population of blue whales is probably as follows:

The blue whale is still considered endangered

Exploitation

The blue whale was been hunted since the late 1800s, both in the Atlantic and the Pacific Oceans. In the 1930-1931 season alone, nearly 30,000 blue whales were killed. Between the 1924-1925 season and the 1970-1971 season an estimated 280,000 blue whales have been killed. Although there were clear indications that this species was overexploited, the IWC declared the blue whale a protected species only in 1966.

Feeding

The blue whale feeds almost exclusively on a few species of Euphausiids (krill). Occasionally they take small fishes and squid. They feed by swallowing or gulping large amounts of water and filtering the water through their baleen when closing the mouth. They probably eat from 2 to 4 tonnes of food per day.

References

Yochem, P.K. and S. Leatherwood (1985)
Blue whale. In: S.H. Ridgway and R.J. Harrison (eds.): Handbook of Marine Mammals, Vol. 3: The Sirenians and Baleen Whales. pp.193-240. Academic Press.
Klinowska, M. (1991)
Dolphins, Porpoises and Whales of the World. The IUCN Red Data Book. IUCN, Gland, Switzerland.
Rice, D.W. (1998)
Marine mammals of the world - Systematics and distribution
Society of Marine Mammalogy Special Publication Number 4, 231 pp.


Note on the pictures

The photos on this page were taken on a whale-watching trip out of Monterey, California, in November 1986. A number of blue whales had just moved into Monterey Bay prior to the trip. This whale-watching trip was organized as part of the Second Biennial Conference and Symposium of the American Cetacean Society, November 21-23, 1986, in Monterey. Although the weather conditions were rough (6 Beaufort winds) a number of blue whales and Dall's porpoises were spotted.


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