Humpback whale

From Encyclopedia Westarctica
Jump to navigation Jump to search
Humpback whale underwater

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, making it popular with whale watchers. 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 in polar waters, and migrate to tropical or subtropical waters to breed and give birth 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.

Like other large whales, the humpback was a target for the whaling industry. Once hunted to the brink of extinction, its population fell by an estimated 90% before a 1966 moratorium. While stocks have partially recovered, entanglement in fishing gear, collisions with ships and noise pollution continue to impact the population of 80,000.

Behavior

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. Humpback whales often leap out of the water, a behavior known as "breaching", and slap the water with their fins or tails.

Song

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, instead, they produce sound via a larynx like structure found in the throat, the mechanism of which has not as of yet been clearly identified. Whales do not have to exhale to produce sound.

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, snorts and barks.

Breathing

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 they must continue to breathe. Possibly only half of their brain sleeps at one time, with one half managing the surface-blow-dive process without awakening the other half.

Diet and predation

Humpback whale breaching

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 juvenile Atlantic and Pacific salmon, herring, capelin and American sand lance, as well as Atlantic mackerel, pollock and haddock in the North Atlantic. They have been documented opportunistically feeding near fish hatcheries in Southeast Alaska, feasting on salmon fry released from the hatcheries. 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.

Orcas

Visible scars indicate that killer whales can prey upon juvenile humpbacks, though until recently hunting had never been witnessed and attacks were assumed to be superficial in nature. However, a 2014 study off Western Australia observed that 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 killer whales who are attacking either humpback calves or juveniles as well as members of other species.

Whaling

Humpback whales were hunted as early as the 18th century. By the 19th century, many nations (the United States in particular), were hunting the animal heavily in the Atlantic Ocean and to a lesser extent in the Indian and Pacific Oceans. The late-19th-century introduction of the explosive harpoon allowed whalers to accelerate their take. This, along with hunting in the Southern Ocean beginning in 1904, sharply reduced whale populations. During the 20th century, over 200,000 humpbacks were taken, reducing the global population by over 90%. North Atlantic populations dropped to as low as 700 individuals.

Ban

In 1946, the International Whaling Commission (IWC) was founded to oversee the industry. They imposed hunting regulations and created hunting seasons. To prevent extinction, IWC banned commercial humpback whaling in 1966. By then, the global population had been reduced to around 5,000. The ban has remained in force since 1966.

Prior to commercial whaling, populations could have reached 125,000. North Pacific kills alone are estimated at 28,000. The Soviet Union deliberately under-recorded its catches; the Soviets reported catching 2,820 between 1947 and 1972, but the true number was over 48,000.

As of 2004, hunting was restricted to a few animals each year off the Caribbean island of Bequia in the nation of St. Vincent and the Grenadines. The take is not believed to threaten the local population. Japan had planned to kill 50 humpbacks in the 2007/08 season under its JARPA II research program. The announcement sparked global protests. After a visit to Tokyo by the IWC chair asking the Japanese for their co-operation in sorting out the differences between pro- and antiwhaling nations on the commission, the Japanese whaling fleet agreed to take no humpback whales during the two years it would take to reach a formal agreement. In 2010, the IWC authorized Greenland's native population to hunt a few humpback whales for the following three years.

In Japan, humpback, minkes, sperm and many other smaller Odontoceti, including critically endangered species such as North Pacific right, western gray and northern fin, have been targets of illegal captures. The hunts use harpoons for dolphin hunts or intentionally drive whales into nets, reporting them as cases of entanglement. Humpback meat can be found in markets. In one case, humpbacks of unknown quantities were illegally hunted in the Exclusive Economic Zones of anti-whaling nations such as off Mexico and South Africa.