Rorquals () are the largest group of baleen whales, comprising the family Balaenopteridae, which contains nine extant species in two genera. They include the largest animal ever known to have lived, the blue whale, which can reach , and the fin whale, which reaches ; the smallest of the group, the northern minke whale, reaches .

Rorquals take their name from French , which derives from the Norwegian word : the first element originated from the Old Norse name for this type of whale, , probably related to the Norse word for "red", and the second from the Norse word hvalr meaning "whale" in general. The family name Balaenopteridae is from the type genus, Balaenoptera.

Characteristics

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 furrows allow the mouth to expand immensely when feeding. These "pleated throat grooves" distinguish balaenopterids from other whales.

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. Rice's whale has the smallest distribution of rorquals and possibly baleen whales in general, being endemic to a small portion of the Gulf of Mexico west of the Florida peninsula and south of Alabama and the Florida panhandle, although it likely formerly had a much wider distribution in the Gulf.

Most rorquals are strictly oceanic: the exceptions are the gray whale, Bryde's whale, Eden's whale, and Rice'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

thumb|Humpback feeding on young [[Alaska pollock|pollock off Alaska]]

As well as other methods, rorquals obtain prey by lunge-feeding on bait balls. 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 brains to coordinate the engulfment action. Furthermore, their large nerves are flexible so that they can stretch and recoil. In fact, they give rorquals the ability to open their mouths so wide that they would be capable of taking in water at volumes greater than their own sizes.<!--

Taxonomy

thumb|[[Cladogram of the family Balaenopteridae using complete mtDNA sequences and short interspersed repetitive element (SINE) insertion data.]]

thumb|Skeleton of the extinct [[Plesiobalaenoptera|Plesiobalaenoptera hubachi at the Museum für Naturkunde, Berlin]]

Formerly, the rorqual family Balaenopteridae was split into two subfamilies, the Balaenopterinae and the Megapterinae, with each subfamily containing 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. Two genetic studies, one in 2018 and one in 2020, suggest that the gray whale (Eschrichtius robustus) be counted among the rorquals, being more derived than the two minke whales but basal to the humpback whale, fin whale, and the other taxa classified in Balaenoptera.

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. The discovery of the highly endangered Rice's whale was announced in 2021 after a genetic study found it to be distinct from Bryde's whale; this species is known from a small portion of the northeastern Gulf of Mexico.

Extant species

  • Family Balaenopteridae: Rorquals
  • Balaenoptera
  • Fin whale, Balaenoptera physalus
  • Northern fin whale, Balaenoptera physalus physalus
  • Southern fin whale, Balaenoptera physalus quoyi
  • Sei whale, Balaenoptera borealis
  • Bryde's whale, Balaenoptera edeni
  • Eden's whale, Balaenoptera edeni edeni
  • Rice's whale, Balaenoptera ricei
  • Blue whale, Balaenoptera musculus
  • Pygmy blue whale, Balaenoptera musculus brevicauda
  • Common minke whale, Balaenoptera acutorostrata
  • Antarctic minke whale, Balaenoptera bonaerensis
  • Omura's whale, Balaenoptera omurai
  • Megaptera
  • Humpback whale, Megaptera novaeangliae

Fossil genera

  • Archaebalaenoptera
  • Archaeschrichtius
  • Cetotheriophanes
  • Diunatans
  • Eschrichtioides
  • Gricetoides
  • Incakujira
  • Miobalaenoptera
  • Nehalaennia
  • Parabalaenoptera
  • Plesiobalaenoptera
  • Plesiocetus
  • Praemegaptera
  • Protororqualusthumb|Incakujira anilliodefuego [[paratype]]

Alternative generic taxonomy for living rorquals

In 2012, the following alternate taxonomy was presented:

  • Balaenoptera
  • Fin whale, Balaenoptera physalus
  • Megaptera
  • Humpback whale, Megaptera novaeangliae
  • Pterobalaena
  • Common minke whale, Pterobalaena acutorostrata
  • Antarctic minke whale, Pterobalaena bonaerensis
  • Rorqualus
  • Sei whale, Rorqualus borealis
  • Bryde's whale, Rorqualus brydei
  • Eden's whale, Rorqualus edeni
  • Blue whale, Rorqualus musculus
  • Omura's whale, Rorqualus omurai

References

Notes

Sources

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