The humpback whale (Megaptera novaeangliae) is a Baleen whale. One of the larger rorqual species, adults range in length from 12–16 metres (40–50 ft) and weigh approximately 36,000 kilograms (79,000 lb). The humpback has a distinctive body shape, with unusually long pectoral fins and a knobbly head. It is an acrobatic animal, often breaching and slapping the water. Males produce a complex whale song, which lasts for 10 to 20 minutes and is repeated for hours at a time. The purpose of the song is not yet clear, although it appears to have a role in mating.

Found in oceans and seas around the world, humpback whales typically migrate up to 25,000 kilometres each year. Humpbacks feed only in summer, in polar waters, and migrate to tropical or sub-tropical waters to breed and give birth in the winter. During the winter, humpbacks fast and live off their fat reserves. The species’ diet consists mostly of krill and small fish. Humpbacks have a diverse repertoire of feeding methods, including the spectacular bubble net feeding technique.

Like other large whales, the humpback was and is a target for the whaling industry. Due to over-hunting, its population fell by an estimated 90% before a whaling moratorium was introduced in 1966. Stocks of the species have since partially recovered; however, entanglement in fishing gear, collisions with ships, and noise pollution also remain concerns. There are at least 80,000 humpback whales worldwide. Once hunted to the brink of extinction, humpbacks are now sought out by whale-watchers, particularly off parts of Australia and the United States.

Description and lifecycle

Humpback whales can easily be identified by their stocky bodies with obvious humps and black dorsal colouring. The head and lower jaw are covered with knobs called tubercles, which are actually hair follicles and are characteristic of the species. The tail flukes, which are lifted high in some dive sequences, have wavy trailing edges. There are four global populations, all being studied. North Pacific, Atlantic, and southern ocean humpbacks have distinct populations which make an annual migration. One population in the Indian Ocean does not migrate. The Indian Ocean has a northern coastline, while the Atlantic and Pacific oceans do not, thereby preventing the humpbacks from migrating to the pole.

The long black and white tail fin, which can be up to a third of body length, and the pectoral fins have unique patterns, which enable individual whales to be recognised. Several suggestions have been made to explain the evolution of the humpback’s pectoral fins, which are proportionally the longest fins of any cetacean. The two most enduring hypotheses are the higher maneuverability afforded by long fins, or that the increased surface area is useful for temperature control when migrating between warm and cold climates. Humpbacks also have ‘rete mirable’ a heat exchanging system, which works similarly to the same structured system in certain species of sharks and other fish.

Humpbacks have 270 to 400 darkly coloured baleen plates on each side of the mouth. The plates measure from a mere 18 inches (460 mm) in the front to approximately 3 feet (0.91 m) long in the back, behind the hinge. Ventral grooves run from the lower jaw to the umbilicus about halfway along the bottom of the whale. These grooves are less numerous (usually 16–20) and consequently more prominent than in other rorquals. The stubby dorsal fin is visible soon after the blow when the whale surfaces, but has disappeared by the time the flukes emerge. Humpbacks have a distinctive 3 m (10 ft) heart shaped to bushy blow, or exhalation of water through the blowholes. Early whalers also noted blows from humpback adults to be 10 - 20 feet (6.1 m) high. Whaling records show they understood each specie has its own distinct shape and height of blows.

Newborn calves are roughly the length of their mother’s head. A 50-foot (15 m) mother would have a 20-foot (6.1 m) newborn weighing in at 2 short tons (1.8 M/T). They are nursed by their mothers for approximately six months, then are sustained through a mixture of nursing and independent feeding for possibly six months more. Humpback milk is 50% fat and pink in color. Some calves have been observed alone after arrival in Alaskan waters. Females reach sexual maturity at the age of five with full adult size being achieved a little later. According to new research, males reach sexual maturity at approximately 7 years of age. Fully grown the males average 15–16 m (49–52 ft), the females being slightly larger at 16–17 m (52–56 ft), with a weight of 40,000 kg (or 44 tons); the largest 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 killed in the Caribbean. She was 88 feet (27 m) long, weighing nearly 90 tons.

Females have a hemispherical lobe about 15 centimetres (6 in) in diameter in their genital region. This allows males and females to be distinguished if the underside of the whale can be seen, even though the male’s penis usually remains unseen in the genital slit. Male whales have distinctive scars on heads and bodies, some resulting from battles over females.

Females typically breed every two or three years. The gestation period is 11.5 months, yet some individuals can breed in two consecutive years. Humpback whales were thought to live 50–60 years, but new studies using the changes in amino acids behind eye lenses proved another baleen whale, the Bowhead, to be 211 years old. This was an animal taken by the Inuit off Alaska. More studies on ages are currently being done.

Social structure and courtship

The humpback social structure is loose-knit. Usually, individuals live alone or in small transient groups that assemble and break up over the course of a few hours. Groups may stay together a little longer in summer in order to forage and feed cooperatively. Longer-term relationships between pairs or small groups, lasting months or even years, have been observed, but are rare. Recent studies extrapolate feeding bonds observed with many females in Alaskan waters over the last 10 years. It is possible some females may have these bonds for a lifetime. More studies need to be done on this. The range of the humpback overlaps considerably with many other whale and dolphin species — whilst it may be seen near other species (for instance, the Minke Whale), it rarely interacts socially with them. Humpback calves have been observed in Hawaiian waters playing with bottlenose dolphin calves.

Courtship rituals take place during the winter months, when the whales migrate toward the equator from their summer feeding grounds closer to the poles. Competition for a mate is usually fierce, and female whales as well as mother-calf dyads are frequently trailed by unrelated male whales dubbed escorts by researcher Louis Herman. Groups of two to twenty males typically gather around a single female and exhibit a variety of behaviours in order to establish dominance in what is known as a competitive group. The displays may last several hours, the group size may ebb and flow as unsuccessful males retreat and others arrive to try their luck. Techniques used include breaching, spy-hopping, lob-tailing, tail-slapping, flipper-slapping, charging and parrying. “Super pods” have been observed numbering more than 40 males, all vying for the same female. (M. Ferrari et. al)

Whale song is assumed to have an important role in mate selection; however, scientists remain unsure whether the song is used between males in order to establish identity and dominance, between a male and a female as a mating call, or a mixture of the two. All these vocal and physical techniques have also been observed while not in the presence of potential mates. This indicates that they are probably important as a more general communication tool. Recent studies showed singing males attract other males. Scientists are extrapolating possibilities the singing may be a way to keep the migrating populations connected. (Ferrari, Nicklin, Darling, et al.) It has also been noted that the singing begins when the competition ends. Studies on this are ongoing.

Feeding

The species feeds only in summer and lives off fat reserves during winter. Humpback whales will only feed rarely and opportunistically while in their wintering waters. It is an energetic feeder, taking krill and small schooling fish, such as herring (Clupea harengus), salmon, capelin (Mallotus villosus) and sand lance (Ammodytes americanus) as well as Mackerel (Scomber scombrus), pollock (Pollachius virens) and haddock (Melanogrammus aeglefinus) in the North Atlantic. Krill and Copepods have been recorded from Australian and Antarctic waters. It hunts fish by direct attack or by stunning them by hitting the water with its pectoral fins or flukes.

The humpback has the most diverse repertoire of feeding methods of all baleen whales. Its most inventive technique is known as bubble net feeding: a group of whales blows bubbles while swimming in circles to create a ring of bubbles. The ring encircles the fish, which are confined in an ever-tighter area as the whales swim in a smaller and smaller circles. The whales then suddenly swim upward through the bubble net, mouths agape, swallowing thousands of fish in one gulp. This technique can involve a ring of bubbles up to 30 m (100 ft) in diameter and the cooperation of a dozen animals. Some of the whales take the task of blowing the bubbles through their blowholes, some dive deeper to drive fish toward the surface, and others herd fish into the net by vocalizing. Humpbacks have been observed bubblenet feeding alone as well.

Song

Both male and female humpback whales can produce sounds, however only the males produce the long, loud, complex “songs” for which the species is famous. Each song consists of several sounds in a low register that vary in amplitude and frequency, and typically lasts from 10 to 20 minutes. Songs may be repeated continuously for several hours; humpback whales have been observed to sing continuously for more than 24 hours at a time. As cetaceans have no vocal cords, whales generate their song by forcing air through their massive nasal cavities.

Whales within an area sing the same song, for example all of the humpback whales of the North Atlantic sing the same song, and those of the North Pacific sing a different song. Each population’s song changes slowly over a period of years —never returning to the same sequence of notes.

Scientists are still unsure of the purpose of whale song. Only male humpbacks sing, so it was initially assumed that the purpose of the songs was to attract females. However, many of the whales observed to approach singing whales have been other males, with the meeting resulting in a conflict. Thus, one interpretation is that the whale songs serve as a threat to other males. Some scientists have hypothesized that the song may serve an echolocative function. During the feeding season, humpback whales make altogether different vocalizations, which they use to herd fish into their bubble nets.

Conservation

Internationally this species is considered vulnerable. Most monitored stocks of humpback whales have rebounded well since the end of the commercial whaling era, such as the North Atlantic where stocks are now believed to be approaching pre-hunting levels. However, the species is considered endangered in some countries where local populations have recovered slowly, including the United States.

Today, individuals are vulnerable to collisions with ships, entanglement in fishing gear, and noise pollution. Like other cetaceans, humpbacks are sensitive to noise and can even be injured by it. In the 19th century, two humpback whales were found dead near sites of repeated oceanic sub-bottom blasting, with traumatic injuries and fractures in the ears.

Once hunted to the brink of extinction the humpback whale has made a dramatic comeback in the North Pacific Ocean. A study released May 22, 2008 estimates that the humpback whale population that hit a low of 1,500 whales before hunting was banned worldwide, has made a comeback to a population of between 18,000 and 20,000.

The ingestion of saxitoxin, a Paralytic shellfish poisoning (PSP) from contaminated mackerel has been implicated in humpback whale deaths.

Some countries are creating action plans to protect the humpback; for example, in the United Kingdom, the humpback whale has been designated as a priority species under the national Biodiversity Action Plan, generating a set of actions to conserve the species. The sanctuary provided by National Parks such as Glacier Bay National Park and Preserve and Cape Hatteras National Seashore, among others, have also become a major factor in sustaining the populations of the species in those areas.

Although much was known about the humpback whale due to information obtained through whaling, the migratory patterns and social interactions of the species were not well known until two separate studies by R. Chittleborough and W. H. Dawbin in the 1960s. Roger Payne and Scott McVay made further studies of the species in 1971. Their analysis of whale song led to worldwide media interest in the species, and left an impression in the public mind that whales were a highly intelligent cetacean species, a contributing factor to the anti-whaling stance of many countries.

From Wikipedia: http://en.wikipedia.org/wiki/Humpback_Whale