| Rorquals[1] | |
|---|---|
| Humpback Whale, Megaptera novaeangliae | |
| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Mammalia |
| Order: | Cetacea |
| Suborder: | Mysticeti |
| Superfamily: | Balaenopteroidea |
| Family: | Balaenopteridae Gray, 1864 |
| Genera | |
Rorquals ( /ˈrɔrkwəl/) 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 (170 short tons), and another that easily reaches 50 tonnes (55 short tons); even the smallest of the group, the Northern Minke Whale, reaches 9 tonnes (9.9 short tons).
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Rorquals take their name from French rorqual, which itself derives from the Norwegian word røyrkval, meaning "furrow whale".[2] 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 immensely when feeding. The "Minke" is allegedly named after a Norwegian whaler named Meincke, who mistook a Northern Minke Whale for a Blue Whale.[3] [4]
Rorquals are slender and streamlined in shape, compared with their relatives the right whales, and most have narrow, elongated flippers. They have a dorsal fin, situated far back on the body, near to the tail. Rorquals feed by gulping in water, and then pushing it out through the baleen plates with their tongue. They feed on crustaceans, such as krill, but also on various fish, such as herrings and sardines.[5]
Gestation in rorquals lasts 11–12 months, so that both mating and birthing occur at the same time of year. Mothers give birth to a single young, which is weaned after 6–12 months, depending on species.[5] Of some species, adults live in small herds, or "pods" of two to five individuals. For example, Humpback whales have a fluid social structure, often engaging behavioral practices in a pod, other times being solo—not necessarily living together.
Distribution is worldwide: the Blue, Fin, Humpback, and the Sei Whales are found in all major oceans; the Common (Northern) and Antarctic (Southern) Minke Whale species are found in all the oceans of their respective hemispheres; and either of Bryde's Whale and Eden's Whale occur in the Atlantic, Pacific, and Indian oceans, being absent only from the cold waters of the Arctic and Antarctic.
Most rorquals are strictly oceanic: the exceptions are Bryde's Whale and Eden's Whale (which are usually found close to shore all year round) and the Humpback Whale (which is oceanic but passes close to shore when migrating). It is the largest and the smallest types—the Blue Whale and Antarctic Minke Whale—that occupy the coldest waters in the extreme south; the Fin Whale tends not to approach so close to the ice shelf; the Sei Whale tends 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 warmer waters 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.
As well as other methods, rorqual whales obtain prey by lunge feeding on bait balls.[6] Lunge feeding is an extreme feeding method, where the whale accelerates to a high velocity and then opens its mouths to a large gape angle. This generates the water pressure required to expand its mouth and engulf and filter a huge amount of water and fish. According to Potvin and Goldbogen, lunge feeding in rorqual whales represents the largest biomechanical event on Earth.[7]
Formerly the rorqual family Balaenopteridae was split into two subfamilies, Balaenopterinae and Megapterinae, with each subfamily contained one genus, Balaenoptera and Megaptera respectively. However, the phylogeny of the various rorqual species shows the current division is paraphyletic, and in 2005 the division into subfamilies was dropped.[8]
The discovery of a new species in Balaenopteridae, Omura's whale (Balaenoptera omurai), was announced in November 2003, which looks similar to, if smaller than, the Fin Whale were found in Indo-Pacific waters.
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