Blue whale  (Balaenoptera musculus)

Classified as Endangered (EN) on the IUCN Red List. Listed on Appendix I of CITES and Appendix I of the Convention on Migratory Species (CMS or Bonn Convention). Subspecies: Antarctic blue whale, B. m. intermedia, is classified as Critically Endangered (CR); the pygmy blue whale, B. m. brevicauda, is classified as Data Deficient (DD) and the North Atlantic stock of the North Atlantic blue whale, B. m. musculus, is classified as Vulnerable (VU) on the IUCN Red List (1).

The blue whale is the largest animal to have ever lived, almost as big as a Boeing 737 (4), and even larger than the biggest dinosaurs (2). The skin is greyish blue in colour (5) with a mottled effect visible in some lights that can allow individuals to be identified (6). The underside, especially of whales living in polar waters, often has a yellowish tinge caused by microscopic algae (diatoms), and between 55 and 88 throat grooves run from under the chin to the navel (3). The blow (or spout) of this species is the biggest amongst all whales; the slender upright column of air can rise to nine meters (6).

Found in the Atlantic, Pacific, Arctic and Indian Oceans, with a range that extends from the periphery of drift-ice in polar seas to the tropics (5). Three main populations persist: one in the southern hemisphere, one in the North Pacific and one in the North Atlantic (4). It is thought that less than 5,000 individuals remain (3).

The blue whale inhabits the open ocean, where it is found most frequently along the continental shelf edge and near polar ice (3).

Blue whales usually occur alone or in groups numbering between two and three individuals, but occasionally large groups of up to 60 individuals may form in areas of high food abundance (7). They feed mainly on shrimp-like krill, which are filtered through the baleen plates (7). Whales tend to feed at less than 100 metres deep, and make dives lasting between 5 and 20 minutes (7). Most blue whales are thought to spend the summer feeding in the colder waters of high latitudes, migrating to warm waters in the winter where females give birth (5); although some may be resident in the same area year round (3). No feeding occurs on the breeding grounds. The two main populations (north and south) remain separated as the seasons are reversed in the two hemispheres.

A single calf is produced after a gestation period of 10 to 11 months. The inter-birth period is probably two to three years, although this may have decreased recently in response to the low population densities (7). At birth, a calf measures about 7 m in length (3) and may consume up to 50 gallons of milk a day in its first year of life, leading to a weight gain of 90 kilograms a day (6). Communication seems to occur via a variety of low frequency sounds and clicks (7).

As blue whales are so large, fast for their size and difficult to find, they were not targeted by the whaling industry until technological advances between 1860 and 1920 made capture possible (5). By the 1960s such large numbers had been killed that the species was thought to be on the very brink of extinction (5). This whale is still threatened by pollution, and blue whale meat still turns up on markets in Japan (4).

Hunting of the blue whale has been banned since 1966 (4), however they have been hunted since by illegal soviet whaling. International trade is forbidden as the species is listed on Appendix I of the Convention on International Trade in Endangered Species (CITES) (8). Populations in the Southern Hemisphere are now gradually increasing (9), but the species still remains in a precarious position.

For further information on the blue whale, see:

• Carwardine, M, Hoyt, E, Fordyce, R.E., and Gill, P. (1998) Whales and Dolphins. Harper Collins Publishers, London.
• The Whale and Dolphin Conservation Society (WDCS):
  http://www.wdcs.org/
• BBC Wildlife Finder:
  http://www.bbc.co.uk/nature/species/Blue_Whale

For the most current estimates of whale populations see the International Whaling Commission:
http://www.iwcoffice.org/conservation/estimate.htm

This information is awaiting authentication by a species expert, and will be updated as soon as possible. If you are able to help please contact:
arkive@wildscreen.org.uk

• Baleen: in some whales, the comb-like fibrous plates hanging from the upper jaw that are used to sieve food from sea water. These are often referred to as whalebone.
• Subspecies: a population usually restricted to a geographical area that differs from other populations of the same species, but not to the extent of being classified as a separate species.

1. IUCN Red List (January, 2009)
   http://www.iucnredlist.org
2. Macdonald, D. (2001) The New Encyclopaedia of Mammals. Oxford University Press, Oxford.
3. WDCS. (2002) Pers. comm.
4. WDCS (February, 2002)
   http://www.wdcs.org/dan/publishing.nsf/allweb/803E6F754FC6728380256966005087B7
5. Animal Diversity Web (February, 2002)
   http://animaldiversity.ummz.umich.edu/
6. Carwardine, M., Hoyt, E., Fordyce, R.E. and and Gill, P. (1998) Whales and Dolphins. Harper Collins Publishers, London.
7. Animal Info (February, 2002)
   http://www.animalinfo.org/species/cetacean/balamusc.htm
8. UNEP-WCMC database (October, 2002)
   http://quin.unep-wcmc.org/
9. International Whaling Commission (June, 2007)
   http://www.iwcoffice.org/conservation/estimate.htm