A Humpback Whale
Rorquals(family Balaenopteridae) are the largest group of baleen whales, with nine extant species in two genera. They include the largest animal that has ever lived, the blue whale, which can reach 180 tonnes (200 short tons), and the fin whale, which reaches 120 tonnes (130 short tons); even the smallest of the group, the northern minke whale, reaches 9 tonnes (9.9 short tons).
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, "permitting them to engorge great mouthfuls of food and water in a single gulp." These "pleated throat grooves" distinguish balaenopterids from other whales. 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 about two-thirds the way back. 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. Gestation in rorquals lasts 11–12 months, so that both mating and birthing occur at the same time of year. Cows give birth to a single calf, which is weaned after 6–12 months, depending on species. Of some species, adults live in small groups, 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 solitary.
Distribution and habitat
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 tropical waters during the winter, then migrate back to the polar feeding grounds rich in plankton and krill for the short polar summer.
Genus †Cetotheriophanes Cetotheriophanes capellinii Genus †Diunatans Diunatans luctoretemergo Genus †Parabalaenoptera Parabalaenoptera baulinensis Genus †Plesiobalaenoptera Plesiobalaenoptera quarantellii Genus †Plesiocetus Plesiocetus garopii
Genus Balaenoptera Fin Whale, Balaenoptera physalus Sei Whale, Balaenoptera borealis Bryde's Whale, Balaenoptera brydei Eden's Whale, Balaenoptera edeni Blue Whale, Balaenoptera musculus Common Minke Whale, Balaenoptera acutorostrata Antarctic Minke Whale, Balaenoptera bonaerensis Omura's Whale, Balaenoptera omurai †Balaenoptera hubachi
Genus Megaptera Humpback Whale, Megaptera novaeangliae