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Balaenoptera Megaptera |
Rorquals are the largest group of baleen whales, with nine species in two genera. They include the largest animal that has ever lived, the Blue Whale, which can reach 150 tonnes, two others that easily pass 50 tonnes, and even the smallest of the group, the Northern Minke Whale, reaches 9 tonnes.
Rorquals take their name from a Norwegian word meaning "furrow whale": all members of the family have a series of longitudinal folds of skin running from below the mouth back to the navel (except the Sei Whale, which has shorter grooves). These are understood to allow the mouth to expand greatly when feeding. "Minke" is named after a Norwegian or German whaling gunner named Meincke, who, in the early part of the 20th century shot a Northern Minke Whale mistaking it for a Blue.
Distribution is worldwide: the Blue, Fin, Humpback, Sei, and Minke Whales are found in all major oceans; and one or other of the two species of Bryde's Whale occurs in the Atlantic, Pacific, and Indian oceans, being absent only from the cold waters of the Arctic and Antarctic.
Most rorquals are fairly strictly oceanic: the exceptions are Bryde's Whales (which are usually found close to shore all year round) and Humpback Whales (which are oceanic but pass close to shore when migrating). Oddly, it is the largest and the smallest types - Blue and Minke Whales - that occupy the coldest waters in the extreme south; Fin Whales tend not to approach so close to the ice shelf; Sei Whales tend to stay further north again. (In the northern hemisphere, where the continents distort weather patterns and ocean currents, these movements are less obvious, although still present.) Within each species, the largest individuals tend to approach the poles more closely, while the youngest and fittest ones tend to stay in the south (or north) for longer before leaving on their annual migration.
Most rorquals breed in temperate waters during the winter, then migrate back to the polar feeding grounds rich in plankton and krill for the short polar summer.
The discovery of an eighth member of the Balaenopteridae family was announced in November 2003 - specimens of the Balaenoptera omurai, which looks similar to, if smaller than, the Fin Whale were found in Indo-Pacific waters.
Taxonomically the Balaenopteridae (rorqual) family is split into two sub-families - Balaenopterinae and Megapterinae. Each sub-family contains one genus - Balaenoptera and Megaptera respectively.