|This page uses Creative Commons Licensed content from Wikipedia (view authors).|
|Reproduction||Sexual; give live birth|
|Average Weight||79,000 lb (36,000 kg)|
|Average Length||39–52 ft (12–16 m)|
|Feeding Behavior||Carnivorous / Filter Feeder|
The Humpback Whale (Megaptera novaeangliae) is a species of baleen whale. One of the larger rorqual species, adults range in length from 12–16 m (39–52 ft) and weigh about 36,000 kg (79,000 lb). The humpback has a distinctive body shape, with long pectoral fins and a knobbly head. It is known for breaching and other distinctive surface behaviors. Males produce a complex song lasting 10 to 20 minutes, which they repeat for hours at a time. Its purpose is not clear, though it may have a role in mating.
Found in oceans and seas around the world, humpback whales typically migrate up to 25,000 km (16,000 mi) each year. Humpbacks feed only in summer, in polar waters, and migrate to tropical or subtropical waters to breed and give birth in the winter when they fast and live off their fat reserves. Their diet consists mostly of krill and small fish. Humpbacks have a diverse repertoire of feeding methods, including the bubble net technique.
Humpbacks can easily be identified by their stocky body, obvious hump, black dorsal coloring and elongated pectoral fins. The head and lower jaw are covered with knobs called tubercles, which are hair follicles and are characteristic of the species. The fluked tail, which typically rises above the surface when diving, has wavy trailing edges.
Humpbacks have 270 to 400 darkly colored baleen plates on each side of their mouths. The plates measure from 18 in (46 cm) in the front to about 3 ft (0.91 m) in the back, behind the hinge.
Ventral grooves run from the lower jaw to the umbilicus, about halfway along the underside of the body. These grooves are less numerous (usually 14–22) than in other rorquals, but are fairly wide.
The female has a hemispherical lobe about 15 cm (5.9 in) in diameter in her genital region. This visually distinguishes males and females. The male's penis usually remains hidden in the genital slit.
Fully grown males average 13–14 m (43–46 ft). Females are slightly larger at 15–16 m (49–52 ft); one large recorded specimen was 19 m (62 ft) long and had pectoral fins measuring 6 m (20 ft) each. The largest humpback on record, according to whaling records, was a female killed in the Caribbean; she was 27 m (89 ft) long with a weight of 90 metric tons (99 short tons), although the reliability of this information is unconfirmed due to illogicality of the record. The largest measured by the scientists of the Discovery Committee were a female 14.9 m (49 ft) and a male 14.75 m (48.5 ft), although this was out of a sample size of only 63 whales. Body mass typically is in the range of 25–30 metric tons (28–33 short tons), with large specimens weighing over 40 metric tons (44 short tons).
Newborn calves are roughly the length of their mother's head. At birth, calves measure 6 m (20 ft) at 2 short tons (1.8 t). They nurse for about six months, then mix nursing and independent feeding for possibly six months more. Humpback milk is 50% fat and pink in color.
Females reach sexual maturity at age five, achieving full adult size a little later. Males reach sexual maturity around seven years of age.
The long black and white tail fin can be up to a third of body length. Several hypotheses attempt to explain the humpback's pectoral fins, which are proportionally the longest fins of any cetacean. The higher maneuverability afforded by long fins and the usefulness of the increased surface area for temperature control when migrating between warm and cold climates possibly supported this adaptation.
The varying patterns on the tail flukes distinguish individual animals.
Feeding and predationEdit
Humpbacks feed primarily in summer and live off fat reserves during winter. They feed only rarely and opportunistically in their wintering waters. The humpback is an energetic hunter, taking krill and small schooling fish such as herring, salmon, capelin and American sand lance, as well as Atlantic mackerel, pollock and haddock in the North Atlantic. Krill and copepods are prey species in Australian and Antarctic waters. Humpbacks hunt by direct attack or by stunning prey by hitting the water with pectoral fins or flukes.
The humpback has the most diverse hunting repertoire of all baleen whales. Its most inventive technique is known as bubble net feeding; a group of whales swims in a shrinking circle blowing bubbles below a school of prey. The shrinking ring of bubbles encircles the school and confines it in an ever-smaller cylinder. This ring can begin near 30 m (98 ft) in diameter and involve the cooperation of a dozen animals. Using a crittercam attached to a whale's back, researchers found that some whales blow the bubbles, some dive deeper to drive fish toward the surface and others herd prey into the net by vocalizing. The whales then suddenly swim upward through the "net", mouths agape, swallowing thousands of fish in one gulp. Pleated grooves in the whale's mouth allow the creature to easily drain the water initially taken in, filtering out the prey.
So-called lobtail feeding was observed in the North Atlantic. This technique involves the whale slapping the surface of the ocean with its tail between one and four times before creating the bubble net. Using network-based diffusion analysis, the study authors argued that these whales learned the behavior from other whales in the group over a period of 27 years in response to a change in the primary form of prey.
Visible scars indicate that orcas can prey upon juvenile humpbacks; when available in large numbers, young humpbacks can be attacked and sometimes killed by orcas. Moreover, mothers and (possibly related) adults escort neonates to deter such predation. The suggestion is that when humpbacks suffered near-extinction during the whaling era, orcas turned to other prey, but are now resuming their former practice. There is evidence that humpback whales will defend against or attack these killer whales who are attacking either humpback calves or juveniles as well as members of other species.
The lifespan of rorquals ranges from 45 to 100 years.
The humpback social structure is loose-knit. Typically, individuals live alone or in small, transient groups that disband after a few hours. Groups may stay together longer in summer to forage and feed cooperatively. Longer-term relationships between pairs or small groups, lasting months or even years, have rarely been observed. Some females possibly retain bonds created via cooperative feeding for a lifetime. The humpback's range overlaps with other whale and dolphin species—for instance, the minke whale.
Courtship and reproductionEdit
Courtship rituals take place during the winter months, following migration toward the equator from summer feeding grounds closer to the poles. Competition is usually fierce. Unrelated males, dubbed escorts, frequently trail females, as well as cow-calf pairs. Males gather into "competition groups" around a female and fight for the right to mate with her. Group size ebbs and flows as unsuccessful males retreat and others arrive. Behaviors include breaching, spyhopping, lob-tailing, tail-slapping, pectoral fin-slapping, peduncle throws, charging and parrying.
Whale song is thought to have an important role in mate selection; however, they may also be used between males to establish dominance.
Females typically breed every two or three years. The gestation period is 11.5 months. The peak months for birth are January, February (northern hemisphere), July and August (southern hemisphere). Females wait for one- to two–years before breeding again. Recent research on mitochondrial DNA reveals that groups living in proximity to each other may represent distinct breeding pools.
Humpbacks are a friendly species that interact with other cetacean species such as bottlenose dolphins. Right whales interact with humpbacks. These behaviors have been recorded in all oceans. Records of humpback and southern right whales demonstrating what were interpreted to be mating behaviors have been documented off the Mozambique and Brazilian coasts. Humpback whales appear in mixed groups with other species, such as the blue, fin, minke, gray and sperm whales. Interaction with gray, fin, and right whales have been observed. Teams of researchers observed a male humpback whale singing an unknown type of song and approaching a fin whale at Rarotonga in 2014. One individual was observed playing with a bottlenose dolphin in Hawai'ian waters. Recently, incidents of humpback whales protecting other species of animals such as seals and other whales from killer whales has been documented and filmed. Studies of such incidents indicate that the phenomenon is species-wide and global, with incidents being recorded at various locations across the world.
Both male and female humpback whales vocalize, but only males produce the long, loud, complex "song" for which the species is famous. Each song consists of several sounds in a low register, varying in amplitude and frequency and typically lasting from 10 to 20 minutes. Individuals may sing continuously for more than 24 hours. Cetaceans have no vocal cords. They vocalize by forcing air through their massive nasal cavities (blowholes).
Whales within a large area sing a single song. All North Atlantic humpbacks sing the same song, while those of the North Pacific sing a different song. Each population's song changes slowly over a period of years without repeating.
Scientists are unsure of the purpose of whale songs. Only males sing, suggesting one purpose is to attract females. However, many of the whales observed to approach a singer are other males, often resulting in conflict. Singing may, therefore, be a challenge to other males. Some scientists have hypothesized the song may serve an echolocative function. During the feeding season, humpbacks make unrelated vocalizations for herding fish into their bubble nets.
Humpback whales make other sounds to communicate, such as grunts, groans, "thwops", snorts and barks.
Whales are air-breathing mammals who must surface to get the air they need. The stubby dorsal fin is visible soon after the blow (exhalation) when the whale surfaces, but disappears by the time the flukes emerge. Humpbacks have a 3 m (9.8 ft), heart-shaped to bushy blow through the blowholes.
They do not generally sleep at the surface, but must continue to breathe. Possibly only half of their brain sleeps at one time, allowing the other half to manage the surface/blow/dive process without awakening the other half.
Range and habitatEdit
Humpbacks inhabit all major oceans, in a wide band running from the Antarctic ice edge to 77° N latitude . The four global populations are North Pacific, Atlantic, Southern Ocean and Indian Ocean populations. These populations are distinct. Although the species has cosmopolitan distribution and is usually not considered to cross the equator line, seasonal observations at Cape Verde suggest possible interactions among populations from both hemisphere.
Whales were once uncommon in the eastern Mediterranean or the Baltic Sea, but have increased their presence in both waters as global populations have recovered. They have also returned to Skagerrak and Kattegat, as well as Scandinavian fjords such as the Kvænangen, where they had not been observed for decades.
In the North Atlantic, feeding areas range from Scandinavia to New England. Breeding occurs in the Caribbean and Cape Verde. In the South Atlantic and Indian Oceans, whales may breed off Brazil, as well the coasts of central, southern and southeastern Africa (including Madagascar). Whale visits into Gulf of Mexico have been infrequent, but occurred in the gulf historically. In the South Atlantic, about 10% of world population of the species possibly migrate to Gulf of Guinea. Comparison of songs between those at Cape Lopez and Abrolhos Archipelago indicate that trans-Atlantic mixings between western and southeastern populations occur.
A large population spreads across the Hawai'ian Islands every winter, ranging from the island of Hawai'i in the south to Kure Atoll in the north. These animals feed in areas ranging from the coast of California to the Bering Sea.
A 2007 study identified seven individuals then wintering off the Pacific coast of Costa Rica as having traveled from the Antarctic—around 8,300 km (5,200 mi). Identified by their unique tail patterns, these animals made the longest documented mammalian migration. In Australia, two main migratory populations were identified, off the west and east coasts. These two populations are distinct, with only a few females in each generation crossing between the two groups.
In Panama and Costa Rica, humpback whales come from both the Southern Hemisphere (July–October with over 2,000 whales) and the Northern Hemisphere (December–March numbering about 300.) South Pacific populations migrating off mainland New Zealand, Kermadec Islands, and Tasmania are increasing, but less rapidly than in Australian waters because of illegal whaling by the Soviet Union in the 1970s.
Some recolonizing habitats are confirmed, especially in the North and South Atlantic (e.g. English and Irish coasts, English Channel to coasts in the north such as the North Sea and Wadden Sea, South Pacific (e.g. New Zealand coasts and Niue), pelagic islands of Chile such as Isla Salas y Gómez and the Easter Island where possibilities of undocumented wintering grounds have been considered, southern fiords of Chile and Peru (e.g. Gulf of Penas, Strait of Magellan, Beagle Channel) and in Asia. Areas in the Philippines such as in Babuyan Islands, Cagayan and Calayan and Pasaleng Bay, Ryukyu Islands the Volcano Islands in Japan and the Northern Mariana Islands recently, again became stable/growing wintering grounds while Marshall Islands, Vietnamese, Taiwanese and Chinese coasts show slow or no obvious recovery.
Whales again migrate off Japanese archipelagos and into the Sea of Japan. Connections between these stocks and whales seen in Sea of Okhotsk, on Kamchatka coasts and around Commander Islands have been studied. Historical wintering distributions could have been much wider, as whales were seen areas along Batanes, Sulu and Celebes Seas including off Palawan, Malaysia and Mindanao with higher densities at around today's Cape Eluanbi and Kenting National Park. Unconfirmed sightings have been reported near Borneo in Modern. The first confirmation in modern Taiwan was of a pair off Hualien in 1994, followed by successful escape from entanglement off Taitung in 1999, and continuous sightings around Orchid Island in 2000. Few/none regularly migrate into Kenting National Park. In addition, despite sightings reported almost annually at the islands of Green and Orchid Islands, relatively short stays in these waters indicate recoveries as winter foraging has not occurred. Around Hong Kong, two documented sightings were recorded in 2009 and in 2016. One of the first documented sighting within the Yellow Sea was of a group of 3 or 4 individuals, including a cow calf pair in Changhai County in October, 2015.
Since November 2015, whales gather around Hachijō-jima, far north from the known breeding areas in the Bonin Islands. All breeding activities except for giving births had been confirmed as of January, 2016. That makes Hachijo-jima the northernmost breeding ground in the world, north of breeding grounds such as Amami Ōshima, Midway Island, and Bermuda.
Arabian Sea populationEdit
A non-migratory population in the Arabian Sea remains there year-round. More typical annual migrations cover up to 25,000 km (16,000 mi), making it one of the most-traveled mammalian species. Genetic studies and visual surveys indicate that the Arabian group is the most isolated of all humpback groups and is the most endangered, numbering possibly fewer than 100 animals.
Whales were historically common in continental and marginal waters such as Hallaniyat Islands, along Indian coasts, Persian Gulf and Gulf of Aden and recent migrations into the gulf including by cow-calf pairs. It is unknown whether whales seen in the Red Sea originate in this population, however sightings increased since in 2006 even in the northern part of the sea such as in Gulf of Aqaba. Individuals may reach the Maldives, Sri Lanka, or further east.
Origins of whales occurring at Maldives are not clear as those from Arabian and south Pacific populations are possible.