Humpback whale
The humpback whale is a species of baleen whale. It is a rorqual and is the only species in the genus Megaptera. Adults range in length from and weigh up to. The humpback has a distinctive body shape, with long pectoral fins and tubercles on its head. It is known for breaching and other distinctive surface behaviors, making it popular with whale watchers. Males produce a complex song that typically lasts from 4 to 33 minutes.
Found in oceans and seas around the world, humpback whales typically migrate between feeding areas towards the poles and breeding areas near the equator. Their diet consists mostly of krill and small fish, and they usually use bubbles to catch prey. They are polygynandrous breeders, with both sexes having multiple partners. Males will follow females and fight off rivals. Mothers give birth to calves in shallower water. Orcas are the main natural predators of humpback whales. The bodies of humpbacks host barnacles and whale lice.
Like other large whales, the humpback was a target for the whaling industry. Humans once hunted the species to the brink of extinction: its population fell to around 5,000 by the 1960s. Numbers have partially recovered to some 135,000 animals worldwide, but entanglement in fishing gear, collisions with ships, and noise pollution continue to affect the species.
Taxonomy
The humpback was first identified as baleine de la Nouvelle Angleterre by Mathurin Jacques Brisson in his Regnum Animale of 1756. In 1781, Georg Heinrich Borowski described the species, converting Brisson's name to its Latin equivalent, Balaena novaeangliae. In 1804, Bernard Germain de Lacépède renamed it B. jubartes. In 1846, John Edward Gray created the genus Megaptera, classifying the humpback as Megaptera longipinna, but in 1932, Remington Kellogg reverted the species name to use Borowski's novaeangliae. The common name is derived from the curving of the whales' backs when diving. The genus name, Megaptera, from the Ancient Greek mega- μεγα and ptera πτερα, refer to their large front flippers. The species name means "New Englander" and was probably given by Brisson due to regular sightings of humpbacks off the coast of New England.Humpback whales are rorquals, members of the family Balaenopteridae, which includes the blue, fin, Bryde's, sei, and minke whales. A 2018 genomic analysis estimated that rorquals diverged from other baleen whales in the late Miocene, between 10.5 and 7.5 million years ago. The humpback and fin whales were found to be sister taxa. There is reference to a humpback–blue whale hybrid in the South Pacific, attributed to marine biologist Michael Poole.
Modern humpback whale populations originated in the southern hemisphere around 880,000 years ago and colonized the northern hemisphere 200,000 to 50,000 years ago. A 2014 genetic study suggested that the separate populations in the North Atlantic, North Pacific, and Southern Oceans have had limited gene flow and are distinct enough to be subspecies, with the scientific names of M. n. novaeangliae, M. n. kuzira, and M. n. australis, respectively. A non-migratory population in the Arabian Sea has been isolated for 70,000 years.
Characteristics
The adult humpback whale is generally long, though individuals up to long have been recorded. Females are usually longer than males. The species can reach body masses of. The longest recorded lengths were for a male and for a female. However, records for humpback whales measuring are considered unlikely. Calves are born at around long with a mass of. The species has a bulky body with a thin rostrum and proportionally long flippers, each around one-third of its body length. It has a short dorsal fin that varies from nearly nonexistent to somewhat long and curved. Like other rorquals, the humpback has grooves between the tip of the lower jaw and the navel. The grooves are relatively few in number in this species, ranging from 14 to 35. The upper jaw is lined with baleen plates, which number 540–800 in total and are black in color.The dorsal or upper side of the animal is generally black; the ventral or underside has various levels of black and white coloration. Whales in the southern hemisphere tend to have more white pigmentation. The flippers can vary from all-white to white only on the undersurface. Some individuals may be all white, notably Migaloo who is a true albino. The varying color patterns and scars on the tail flukes distinguish individual animals. The end of the genital slit of the female is marked by a round feature, known as the hemispherical lobe, which visually distinguishes males and females.
Unique among large whales, humpbacks have bumps or tubercles on the head and front edge of the flippers; the tail fluke has a jagged trailing edge. The tubercles on the head are thick at the base and protrude up to. They are mostly hollow in the center, often containing at least one fragile hair that erupts from the skin and is thick. The tubercles develop early in gestation and may have a sensory function, as they are rich in nerves. Sensory nerve cells in the skin are adapted to withstand the high water pressure of diving.
In one study, a humpback whale brain measured long and wide at the tips of the temporal lobes, and weighed around. The humpback's brain has a complexity similar to that of the brains of smaller whales and dolphins. Studies on the brains of humpback whales revealed spindle cells, which, in humans, control theory of mind. The structure of the eye indicates that eyesight is relatively poor, being only able to see silhouettes over long distances and finer details relatively close. Computer models of the middle ear suggest that the humpback can hear at frequencies between 15Hz and 3kHz "when stimulated at the tympanic membrane", and between 200Hz and 9kHz "if stimulated at the thinner region of the tympanic bone adjacent to the tympanic membrane". These ranges are consistent with their vocalization ranges. As in all cetaceans, the respiratory tract of the humpback whale is connected to the blowholes and not to the mouth, although the species appears to be able to unlock the epiglottis and larynx and move them towards the oral cavity, allowing humpbacks to blow bubbles from their mouths. The vocal folds of the humpback are more horizontally positioned than those of land mammals which allows them to produce underwater calls. These calls are amplified by a laryngeal sac.
Behavior and ecology
Humpback whale groups, aside from mothers and calves, typically stay together for days or weeks at the most. They are normally sighted in small groups, though large aggregations form during feeding and among males competing for females. Humpbacks may interact with other cetacean species, such as right whales, fin whales, and bottlenose dolphins. Humpbacks are highly active at the surface, performing aerial behaviors such as breaching, surface slapping with the tail fluke and flippers, and peduncle throws, which involve the tail crashing sideways on the surface. These may be forms of play and communication, and may help to remove parasites. The species is a slower swimmer than other rorquals, cruising at. When threatened, a humpback may speed up to. Their proportionally long pectoral fins give them great propulsion and allow them to swim in any direction, independently of the movements of the tail. Humpbacks are able to flap and rotate their flippers in a manner similar to California sea lions.Humpbacks rest at the surface with their bodies lying horizontally. They frequent shallow seamounts, commonly exploring depths of up to and occasionally diving as deep as. These deeper descents are believed to be for navigational guidance, communication with fellow humpback whales, and facilitation of feeding activities. Dives typically do not exceed five minutes during the summer but are normally 15–20 minutes during the winter. As it dives, a humpback typically raises its tail fluke, exposing the underside. Humpbacks have been observed to produce oral "bubble clouds" when near another individual, possibly in the context of "aggression, mate attraction, or play". Humpbacks may also use bubble clouds as "smoke screens" to escape from predators.
Feeding
Humpback whales feed from spring to fall. They are generalist feeders; their main food items are krill, copepods, other plankton, and small schooling fish. The most common krill species eaten in the southern hemisphere is the Antarctic krill. Farther north, the northern krill and various species of Euphausia and Thysanoessa are consumed. Fish prey include herring, capelin, sand lances, and Atlantic mackerel. Like other rorquals, humpbacks are "gulp feeders", swallowing prey in bulk, while right whales and bowhead whales are skimmers, and the whale increases its mouth gape by expanding the grooves. Water is pushed out through the baleen.In the southern hemisphere, humpbacks have been recorded foraging in large, compact gatherings numbering up to 200 individuals. A study undertaken in May 2009 found a super-aggregation of krill in Wilhelmina Bay, on the west side of the Antarctic Peninsula, with a large number of humpback whales feeding on the krill. Researchers counted a density of 5.1 whales per square kilometer. Smaller and less dense aggregations of krill and whales were also found in Andvord Bay to the south. Krill and humpback whales are abundant in late autumn along the western Antarctic Peninsula, particularly in Wilhelmina Bay, where the whales seem to eat as much as possible in preparation for the winter.
Humpbacks typically hunt their prey with bubble nets, which is considered to be a form of tool use. Bubble-net feeding allows whales to consume more food per mouthful while using less energy; it is particularly useful for low-density prey patches. A group swims in a shrinking circle while blowing air from their blowholes, capturing prey above in a cylinder of bubbles. They may dive up to while performing this technique. Bubble-netting comes in two main forms: upward spirals and double loops. Upward spirals involve the whales blowing air from their blowholes continuously as they circle towards the surface, creating a spiral of bubbles. Double loops consist of a deep, long loop of bubbles that herds the prey, followed by slapping the surface and then a smaller loop of bubbles that precedes the final capture. Combinations of spiraling and looping have been recorded. After the humpbacks create the "nets", the whales swim into them with their mouths gaping and ready to swallow. Bubble-net feeding has also been observed in solitary humpbacks.
Using network-based diffusion analysis, one study argued that whales learned lobtailing from other whales in their group over 27 years in response to a change in primary prey. The tubercles on the flippers stall the angle of attack, which both maximizes lift and minimizes drag. This, along with the shape of the flippers, allows the whales to make the abrupt turns necessary during bubble-feeding.
At Stellwagen Bank off the coast of Massachusetts, humpback whales have been recorded foraging at the seafloor for sand lances. This involves the whales flushing out the fish by brushing their jaws against the bottom.