Rorquals are members of Balaenopteridae, the largest family of baleen whales, characterized by large, streamlined bodies and unique pleated throats. They gulp large quantities of water into their mouth by extending these pleats or grooves, filtering in any prey that enters using their baleen plates. Typically, these whales feed on small fish and crustaceans, like krill and copepods.
There are 9 extant species of rorquals, including some of the largest animals on Earth, the blue whale and the humpback whale. They are found in all major oceans of the world, where they often live in small groups or pods of a few individuals.
The largest animal ever, the blue whale, is a rorqual, and it reaches a maximum length of 98 ft (29.9 m). On average, it weighs around 180 tonnes (200 short tons). Other large species include the fin whale, which reaches a maximum length of 85 ft (26 m) and weighs around 76 to 80 tonnes (85 to 89 short tons). The humpback whale is about 46 to 56 ft (14 to 17 m) long and weighs up to 40 tonnes (44 short tons).
The smallest rorqual, the northern minke whale, weighs around 8.9 tonnes (10 short tons).
They have slender, streamlined bodies characterized by a series of longitudinal, ventral skin folds or grooves that extend from beneath the mouth (the chin and lower jaws) to the navel in most species. In the sei whale and common minke whale, however, the grooves are much shorter.
Most rorqual species have long, narrow flippers and a dorsal fin positioned about two-thirds of the way down their back.
In comparison to other whales, rorquals have reduced nasal and frontal bones in their skull. The nasals and the processes of the premaxillae extend beyond the supraorbital region of the frontal bones. Their rostrum, or snout, is broad and flat, while the supraoccipital bone extends past the zygomatic process of the squamosal bone.
As baleen whales, rorquals possess short and broad baleen plates for feeding.
According to the List of Marine Mammal Species and Subspecies, the 9 extant species of rorquals are currently divided into 2 extant genera: Balaenoptera and Megaptera.
These animals derive their name from the Old Norse word reyðarhvalr, which is a combination of reyðar (meaning fin whale) and hvalr (meaning whale). This term later evolved into røyrkval in Norwegian Nynorsk, which was eventually adopted in French as rorqual.
The family name, Balaenopteridae, hints at the type genus Balaenoptera.
Rorquals are spread worldwide, ranging from the Arctic to the Southern Ocean.
While most rorquals are strictly oceanic, species like the gray whale, Rice’s whale, Bryde’s whale, and Eden’s whale tend to stay near coastal waters. Humpback whales also migrate close to shore. Adult rorquals typically move toward polar regions, while younger individuals remain in warmer waters.
While humpback whales typically feed on small fish, like herrings, capelins, and sardines, other rorquals, such as sei whales and fin whales, consume krill, copepods, and other crustaceans.
When rorquals encounter dense schools of small fish, known as bait balls, they increase their swim speed and expand their mouths wide to gulp the prey. A few species, like fin whales, attain speeds as high as 10.8 km/h before capturing fish. The sudden expansion of the mouth creates low pressure within it, drawing in a massive volume of water along with the prey. This feeding strategy, called lunge feeding, allows large quantities of fish to be captured and filtered through their baleen plates. However, the gray whale is an exception since it typically filters marine sediments from the seafloor.
When rorquals migrate to equatorial latitudes in the fall, they tend to fast, living off the energy derived from their fat-rich blubber.
These animals are expert swimmers. For example, some individuals of blue whales and fin whales have been reported to attain speeds as high as 37 km/h. The sei whale has been found to swim at 65 km/h in short bouts.
In species like humpback whales, adults often form small, temporary groups (pods) of up to five individuals. However, their social structure is flexible, and they may also live alone when necessary.
The lifespan of rorquals varies by species. Minke whales typically live around 45 years, while blue whales can reach a maximum age of 110 years. Fin whales have been recorded living up to 94 years.
Most species breed during winter, particularly in the warm tropical waters. After mating, the females undergo a gestation period of about 11 to 12 months. Thus, both mating and birthing occur at the same time of the year.
Females give birth to a single calf, which is weaned in around 6 to 12 months, depending on the species.
Although they themselves are predators, rorquals are frequently attacked by killer whales.
These whales possess a tiny sensory organ at the mandibular symphysis (joining), which comprises a bundle of mechanoreceptors. This organ helps coordinate the action of the throat pleats while engulfing water.
Of all the extant species of rorquals, six are listed under the IUCN Red List. The sei and blue whales are considered Endangered (EN), the fin whale is Vulnerable (VU), and the Rice’s whale is Critically Endangered (CR). The common minke whale and the humpback whale are listed as Least Concern (LC).
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