Fin whale
Fin whale
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Fin whale

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Fin whale

The fin whale (Balaenoptera physalus), also known as the finback whale or common rorqual, is a species of baleen whale and the second-longest cetacean after the blue whale. The biggest individual reportedly measured 26–27 m (85–89 ft) in length, with a maximum recorded weight of 70 to 80 tonnes (77 to 88 short tons; 69 to 79 long tons). The fin whale's body is long, slender and brownish-gray in color, with a paler underside to appear less conspicuous from below (countershading).

At least two recognized subspecies exist, one in the North Atlantic and one across the Southern Hemisphere. It is found in all the major oceans, from polar to tropical waters, though it is absent only from waters close to the pack ice at the poles and relatively small areas of water away from the open ocean. The highest population density occurs in temperate and cool waters. Its prey mainly consists of smaller schooling fish, small squid, or crustaceans, including copepods and krill. Mating takes place in temperate, low-latitude seas during the winter. Fin whales are often observed in pods of 6–10 animals, with whom they communicate utilizing frequency-modulated sounds, ranging from 16 to 40 hertz.

Like all other large whales, the fin whale was a prized kill during the "heyday" of whaling, from 1840 to 1861. It remained so into the 20th century but decades of overharvesting contributed to declining numbers through the late 20th century. Over 725,000 fin whales were reportedly taken from the Southern Hemisphere between 1905 and 1976. Post-recovery numbers of the southern subspecies are predicted to be less than 50% of the pre-whaling population, even by 2100, due to long-lasting impacts of whaling and slow recovery rates. As of 2018, it was assessed as vulnerable by the IUCN.

The fin whale was first described by Friderich Martens in 1675 and by Paul Dudley in 1725. The former description was used as the primary basis for the species Balaena physalus by Carl Linnaeus in 1758. In 1804, Bernard Germain de Lacépède reclassified the species as Balaenoptera rorqual, based on a specimen that had stranded on Île Sainte-Marguerite (Cannes, France) in 1798. In 1830, Louis Companyo described a specimen that had been stranded near Saint-Cyprien, southern France, in 1828 as Balaena musculus. Most later authors followed him in using the specific name musculus, until Frederick W. True (1898) showed that it referred to the blue whale. In 1846, British taxonomist John Edward Gray described a 16.7 m (55 ft) specimen from the Falkland Islands as Balaenoptera australis. In 1865, German naturalist Hermann Burmeister described a roughly 15 m (49 ft) specimen found near Buenos Aires about 30 years earlier as Balaenoptera patachonicus. In 1903, Romanian scientist Emil Racoviță placed all these designations into Balaenoptera physalus. The word physalus comes from the Greek word physa, meaning "blows," referring to the prominent blow of the species.

Fin whales are rorquals, members of the family Balaenopteridae, which includes the humpback whale, the blue whale, Bryde's whale, the sei whale, and the minke whale. The family diverged from the other baleen whales in the suborder Mysticeti as long ago as the middle Miocene.

Recent DNA evidence indicates the fin whale may be more closely related to the humpback whale (Megaptera novaeangliae) and, in at least one study, the gray whale (Eschrichtius robustus), two whales in different genera, than it is to members of its own genus, such as the minke whales. As of 2023, four subspecies are named, each with distinct physical features and vocalizations. The northern fin whale, B. p. physalus (Linnaeus 1758) inhabits the North Atlantic and the southern fin whale, B. p. quoyi (Fischer 1829) occupies the Southern Hemisphere. Most experts consider the fin whales of the North Pacific to be a third subspecies—this was supported by a 2013 study, which found that the Northern Hemisphere B. p. physalus was not composed of a single subspecies. A 2019 genetic study concluded that the North Pacific fin whales should be considered a subspecies, suggesting the name B. p. velifera (Scammon 1869). The three groups mix at most rarely.

Clarke (2004) proposed a "pygmy" subspecies (B. p. patachonica, Burmeister, 1865) that is purportedly darker in colour and has black baleen. He based this on a single physically mature 19.8 m (65 ft) female caught in the Antarctic in 1947–48, the smaller average size (a few feet) of sexually and physically mature fin whales caught by the Japanese around 50°S, and smaller, darker sexually immature fin whales caught in the Antarctic which he believed were a "migratory phase" of his proposed subspecies. The subspecies has not been genetically established, and is not recognized by the Society for Marine Mammalogy.

The genetic distance between blue and fin whales has been compared to that between a chimpanzee and human (3.5 million years on the evolutionary tree.) Nevertheless, hybrid individuals between blue and fin whales with characteristics of both are known to occur with relative frequency in both the North Atlantic and North Pacific.

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