Humpback Whale

Humpback Whale

The Humpback Whale is a species of baleen whale. One of the larger rorqual species, adults range in length from 12–16 meters (39–52 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 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 (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. 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 bubble net feeding technique.

Like other large whales, the humpback was and is a target for the whaling industry. Due to overhunting, its population fell by an estimated 90% before a whaling moratorium was introduced in 1966. Stocks 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 by whale watchers, particularly off parts of Australia, New Zealand, South America, Canada, and the United States.

Description Edit

A humpback whale can easily be identified by its stocky body with an obvious hump and black dorsal coloring. The head and lower jaw are covered with knobs called tubercles, which are actually hair follicles, and are characteristic of the species. The fluked tail, which it lifts above the surface in some dive sequences, has wavy trailing edges. The four global populations, all under study, are: North Pacific, Atlantic, and Southern Ocean humpbacks, which have distinct populations which complete a migratory round-trip each year, and the Indian Ocean population, which does not migrate, prevented by that ocean's northern coastline.

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 make individual whales identifiable. Several hypotheses attempt to explain the humpback's pectoral fins, which are proportionally the longest fins of any cetacean. The two most enduring mention 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. Humpbacks also have 'rete mirabile', a heat exchanging system, which works similarly in humpbacks, sharks and other fish.

Humpbacks have 270 to 400 darkly coloured baleen plates on each side of their mouths. The plates measure from a mere 18 inches (46 cm) 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 underside of the whale. These grooves are less numerous (usually 14–22) than in other rorquals but are fairly wide.

The stubby dorsal fin is visible soon after the blow when the whale surfaces, but disappears by the time the flukes emerge. Humpbacks have a 3 meters (9.8 ft), heart-shaped to bushy blow, or exhalation of water through the blowholes. Because humpback whales breathe voluntarily, the whales possibly shut off only half of their brains when sleeping. Early whalers also noted blows from humpback adults to be 10–20 feet (3.0–6.1 m) high.

Newborn calves are roughly the length of their mother's head. At birth, calves measure 20 feet (6.1 m) at 2 short tons (1.8 t) The mother, by comparison, is about 50 feet (15 m). They nurse for approximately six months, then mix 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, achieving full adult size a little later. Males reach sexual maturity at approximately seven years of age. Humpback whale lifespans range from 45–100 years. Fully grown, the males average 13–14 m (43–46 ft). Females are slightly larger at 15–16 m (49–52 ft); the largest recorded specimen was 19 meters (62 ft) long and had pectoral fins measuring 6 meters (20 ft) each. 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). The female has a hemispherical lobe about 15 centimeters (5.9 in) in diameter in its genital region. This visually distinguishes males and females. The male's penis usually remains hidden in the genital slit.

Habitat Edit

Humpbacks inhabit all major oceans, in a wide band running from the Antarctic ice edge to 77° N latitude, though not in the eastern Mediterranean or the Baltic Sea.They are migratory, spending summers in cooler, high-latitude waters and mating and calving in tropical and subtropical waters. An exception to this rule is a population in the Arabian Sea, which remains in these tropical waters year-round. Annual migrations of up to 25,000 kilometers (16,000 mi) are typical, making it one of the mammals' best-traveled species.

A large population spreads across the Hawaiian Islands every winter, ranging from the island of Hawaii in the south to Kure Atoll in the north. A 2007 study identified seven individuals wintering off the Pacific coast of Costa Rica as having traveled from the Antarctic—around 8,300 kilometers (5,200 mi). Identified by their unique tail patterns, these animals made the longest documented mammalian migration. In Australia, two main migratory populations have been identified, off the west and east coasts, respectively. These two populations are distinct, with only a few females in each generation crossing between the two groups.

Food Edit

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 Atlantic herring, Atlantic salmon, capelin, and American sand lance, as well as Atlantic mackerel, pollock, and haddock in the North Atlantic. Krill and copepods have been recorded as 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 feeding 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 at up to 30 meters (98 ft) in diameter and involve the cooperation of a dozen animals. Using a crittercam attached to a whale's back, some whales were found to 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. Plated grooves in the whale's mouth allow the creature to easily drain all the water initially taken in.

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