Rorquals (/ˈrɔːrkwəlz/) are the largestgroup ofbaleen whales, comprising thefamilyBalaenopteridae, which contains nineextant species in twogenera. They include the largest known animal that has ever lived, theblue whale, which can reach 180 tonnes (200 short tons), and thefin whale, which reaches 120 tonnes (130 short tons); even the smallest of the group, thenorthern minke whale, reaches 9 tonnes (10 short tons).
Rorquals take their name fromFrenchrorqual, which derives from theNorwegian wordrøyrkval: the first elementrøyr originated from theOld Norse name for this type of whale,reyðr,[3] probably related to the Norse word for "red", and the second from the Norse wordhvalr meaning "whale" in general.[4] The family name Balaenopteridae is from thetype genus,Balaenoptera.
All members of the family have a series of longitudinal folds of skin running from below the mouth back to the navel (except thesei whale andcommon minke whale, which have shorter grooves). These furrows allow the mouth to expand immensely when feeding.[5] These "pleated throat grooves" distinguish balaenopterids from other whales.[5]
Rorquals are slender and streamlined in shape, compared with their relatives theright whales, and most have narrow, elongated flippers. They have a dorsal fin, situated about two-thirds the way back. Most rorquals feed by gulping in water, and then pushing it out through thebaleen plates with their tongue; the exception is thegray whale, which gulps in and filters large amounts of marine sediments from the seafloor. They feed oncrustaceans, such askrill, but also on various fish, such asherrings andsardines.[6]
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 isweaned after 6–12 months, depending on species.[6] 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 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; either ofBryde's whale andEden's whale occur in theAtlantic,Pacific, andIndian oceans, being absent only from the cold waters of theArctic andAntarctic; and the gray whale is found in the northern Pacific Ocean, although it was also found in the Atlantic Ocean in historic times.[7]Rice's whale has the smallest distribution of rorquals and possibly baleen whales in general, beingendemic to a small portion of theGulf of Mexico west of theFloridapeninsula and south ofAlabama and theFlorida panhandle, although it likely formerly had a much wider distribution in the Gulf.[8]
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)[9] and thehumpback 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 andocean 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 inplankton and krill for the short polar summer.
As well as other methods, rorquals obtain prey by lunge-feeding onbait balls.[10]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.[10] In contrast to typical lunge feeding,Gray whales employ a unique suction feeding strategy to capture prey near or on the sea bottom.[11]
Rorquals have a number of anatomical features that enable them to do this, including bilaterally separatemandibles, throat pleats that can expand to huge size, and a unique sensory organ consisting of a bundle ofmechanoreceptors that helps their brains to coordinate the engulfment action.[12] Furthermore, their large nerves are flexible so that they can stretch and recoil.[13] 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. These nerves are packed into a central core area that is surrounded byelastin fibers. Opening the mouth causes the nerves to unfold, and they snap back after the mouth is closed.[13] According to Potvin and Goldbogen, lunge feeding in rorquals represents the largestbiomechanical event on Earth.[14]
Formerly, the rorqual family Balaenopteridae was split into two subfamilies, the Balaenopterinae and theMegapterinae, with each subfamily containing one genus,Balaenoptera andMegaptera, respectively. However, thephylogeny of the various rorqual species shows the current division isparaphyletic, and in 2005, the division into subfamilies was dropped.[15] Two genetic studies, one in 2018 and one in 2020, suggest that thegray whale (Eschrichtius robustus) be counted among the rorquals, being more derived than the twominke whales but basal to thehumpback whale,fin whale, and the other taxa classified inBalaenoptera.[16][17]
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, thefin whale; individuals of this species were found in Indo-Pacific waters. The discovery of the highly endangeredRice's whale was announced in 2021 after a genetic study found it to be distinct fromBryde's whale; this species is known from a small portion of the northeasternGulf of Mexico.[18]
^abMinasian, Stanley M.; Balcomb, Kenneth C.; Foster, Larry, eds. (1984).The World's Whales: The Complete Illustrated Guide. New York: The Smithsonian Institution. p. 18.ISBN978-0-89599-014-3.
^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.S2CID90231.
