Rorqual

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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

Balaenoptera
Megaptera

Rorquals /ˈrɔrkwəl/ (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).

Characteristics

Rorquals take their name from French rorqual, which 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 and common minke whale, which have 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".[3] These "pleated throat grooves" distinguish balaenopterids from other whales.[3]

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.[4]

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.[4] 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.

The "minke" whale is allegedly named after a Norwegian whaler named Meincke, who mistook a northern minke whale for a blue whale.[5][6]

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.

Feeding habits

Humpback feeding on young pollock off Alaska

As well as other methods, rorqual whales obtain prey by lunge feeding on bait balls.[7] Lunge feeding is an extreme feeding method, where the whale accelerates to a high velocity and then opens its mouth 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.

Rorquals have a number of anatomical features that enable them to do this, including bilaterally separate mandibles, throat pleats that can expand to huge size, and a unique sensory organ consisting of a bundle of mechanoreceptors that helps their brain to coordinate the engulfment action.[8] According to Potvin and Goldbogen, lunge feeding in rorqual whales represents the largest biomechanical event on Earth.[9]

Taxonomy

Skeleton of the extinct Balaenoptera hubachi at the Museum für Naturkunde, Berlin

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.[10] The discovery of a new species of balaenopterid, Omura's whale (Balaenoptera omurai), was announced in November 2003, which looks similar to, but smaller than, the fin whale; individuals of this species were found in Indo-Pacific waters.

Alternate generic taxonomy for living rorquals

[12]

References

Wikispecies has information related to: Balaenopteridae

Notes

  1. ↑ Mead, J. G.; Brownell, R. L., Jr. (2005). "Order Cetacea". In Wilson, D. E.; Reeder, D. M. Mammal Species of the World (3rd ed.). Johns Hopkins University Press. pp. 723–743. ISBN 978-0-8018-8221-0. OCLC 62265494. 
  2. ↑ "Etymology of mammal names". IberiaNature - Natural history facts and trivia. Retrieved 2006-12-07. 
  3. ↑ 3.0 3.1 Stanley M. Minasian, Kenneth C. Balcomb, II, and Larry Foster, ed. (1984). The World's Whales: The Complete Illustrated Guide. New York: The Smithsonian Institution. p. 18. ISBN 0-89599-014-8. 
  4. ↑ 4.0 4.1 Gambell, Ray (1984). Macdonald, D, ed. The Encyclopedia of Mammals. New York: Facts on File. pp. 222–225. ISBN 0-87196-871-1. 
  5. ↑ "Dictionary.com". Retrieved 2007-08-30. 
  6. ↑ Lazarus, Sarah (2006). Troubled Waters: The Changing Fortunes of Whales and Dolphins. CSIRO Publishing. Retrieved 2007-08-30. 
  7. ↑ Reeves RR, Stewart BS, Clapham PJ and Powell J A (2002) National Audubon Society Guide to Marine Mammals of the World Chanticleer Press. ISBN 9780375411410.
  8. ↑ Pyenson, ND; Goldbogen JA, Vogl AW, Szathmary G, Drake RL, Shadwick RE (2012). "Discovery of a sensory organ that coordinates lunge feeding in rorqual whales". Nature (Nature Publishing Group) 485 (7399): 498–501. doi:10.1038/nature11135. Retrieved 28 December 2012. 
  9. ↑ Potvin J and Goldbogen JA (2009) "Passive versus active engulfment: verdict from trajectory simulations of lunge-feeding fin whales Balaenoptera physalus J. R. Soc. Interface, 6(40): 1005–1025. doi:10.1098/rsif.2008.0492
  10. ↑ Deméré, T.A.; Berta, A.; McGowen, M.R. (2005). "The taxonomic and evolutionary history of fossil and modern balaenopteroid mysticetes". Journal of Mammalian Evolution 12 (1/2): 99–143. doi:10.1007/s10914-005-6944-3. 
  11. ↑ Thalassotherii in the Paleobiology Database. Retrieved October 2013.
  12. ↑ A. Hassanin, F. Delsuc, A. Rpiquet, C. Hammer, B. J. Vuuren, C. Matthee, M. Ruiz-Garcia, F. Gatzeflis, V. Areskoug, T. T. Nguyen, and A. Couloux. 2012. Pattern and timing of diversification of Cetartiodactyla (Mammalia, Laurasiatheria), as revealed by a comprehensive analysis of mitochondrial genomes. Comptes Rendus Biologies 335:32-50

Sources

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