Blue whale
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Classification:
Population Mondiale
Description Et Histoire Naturelle
Physical DescriptionThe blue whale is the largest animal in the world.
It grows to 24 - 30 meters in length (79 - 98 feet) and perhaps weighs up to 160 tonnes (176 tons). Females are slightly larger than males. Calves are six to seven meters (20 - 23 feet) long at birth.
Blue whales are similar in body shape to other rorqual whales from the family Balaenopteridae. Blue whales have streamlined bodies and broad, flat, u-shaped rostrums similar to fin, sei, Bryde’s and minke whales. There is a large splashguard in front of the two blowholes and one ridge that runs from the front of the blowhole, ending almost at the tip of the rostrum. Blue whales are dark bluish-gray with light-colored blotches over the entire body.
Their flippers are relatively short and tapered and are light or white on the underside. The tail flukes are broad and triangular with a notch in the center and smooth trailing edges. The small dorsal fin is found about three-quarters of the way along the back and, because of the length of the animal, does not appear quickly after the whale blows at the surface. The huge ten meter (33 feet) vertical column of blow can be recognized from a distance. Blue whales have relatively short, black baleen plates and ventral grooves extending at least to the navel.
Natural History
Blue whales inhabit all the world’s oceans, migrating long distances from tropical and temperate waters where calves are born to Arctic and Antarctic waters where they feed almost exclusively on krill. Blue whales tend to remain offshore, but will come closer to feed and perhaps to breed.
There are three subspecies recognized: the "true" blue whale, B. m. musculus, which is found in the North Atlantic and North Pacific; the pygmy blue whale, B. m. brevicauda, which is only found in the Sub-antarctic Zone; and B. m. intermedia, the population that summers in the Antarctic Zone.
Blue whales are usually found singly or in pairs but larger groups can be seen on the feeding grounds. Blue whales may show their tail flukes slightly before a deep dive, which can last between ten and 30 minutes. Some adults have been observed breaching but most are young animals who breach at an angle rather than perpendicular to the surface.
Population parameters for blue whales are not well known. They are thought to reach sexual maturity at about ten years of age. Calves may be born every two or three years following a 12-month gestation period. They are weaned at about eight months and can live up to 90 years.
Today the total "true" blue whale population is not known, but has been estimated at approximately 5,000. Whatever the remaining population, it is only a fraction of pre-exploitation numbers.
Situation De L'Espèce
StatusToday the blue whale is listed as Endangered by the International Union for the Conservation of Nature and Natural Resources (IUCN). It is included on Appendix I of the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES).
Threats to the Species
The blue whale was spared from early hunting by its size, speed (24 - 48 kilometers, or 15 - 30 miles, per hour when chased) and pelagic (open ocean) habits. However, early 20th century whaling technology changed all that and the blue whale became the ultimate whaling target, each animal yielding huge amounts of oil (70 - 120 barrels).
For management purposes, the blue whale became the measure against which all other whale catches were determined. A catch limit (based on oil yield) was set for blue whales with equivalent limits for other species based on their size compared to the blue whale. This was called the Blue Whale Unit (BWU): one blue whale = two fin whales = 2.5 humpback whales = six sei whales. This BWU did nothing to protect the blue whale, which had already been hunted to economic extinction by the 1930s. Provided protection by the International Whaling Commission (IWC) in 1965, the recovery of the blue whale has been slow.
Current threats include disturbance from seismic operations; collision with large vessels; entanglement in fishing gear; pollution (including noise pollution and increasing amounts of plastic debris at sea, oil spills and dumping of industrial wastes).
International Trade
Listed on CITES Appendix I which prohibits international trade.
Auteur Et Sources
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Blue whale. Photo © B Lehnhausen/Photo Researchers, Inc
