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 70,000 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.
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 in the front to approximately 3 feet 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 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.
