Humpback whale
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Classification:
Population mondiale
Description Et Histoire Naturelle
Physical DescriptionThe humpback whale is more robust than minke, Bryde’s, sei, fin and blue whales (the other whales in the family Balaenopteridae), but is not as stocky as the right and bowhead whales.
Adult male humpbacks measure 13 – 14.8 meters (42.7 – 48.6 feet). Females are larger, measuring 13.9 – 15.5 meters (45.6 – 50.9 feet) and weighing between 24.8 – 40.8 tonnes (27.3 – 45 tons). Calves are 4 – 4.6 meters (13 – 15.1 feet). Humpbacks from the Southern Hemisphere are larger on average than those in the Northern Hemisphere.
The flippers are extremely long, measuring up to one third of the total body length – or 4.5 meters (14.8 feet) – and have bumps along the leading edge. The body is generally black or dark gray on the back, and white on the belly. The tail stock is relatively thin and the flukes are concave with a serrated trailing edge. The color of the ventral (underside) fluke varies from all-black to all-white.
Scientists use the different patterns to distinguish between individuals, since each, like human fingerprints, are different.
The dorsal fin is low and broad-based, usually sitting on a hump two-thirds of the way along the bumped back. Variation in the shape of dorsal fins and scarring also help with individual identification.
There are 270 – 400 dark-colored baleen plates measuring 76 centimeters (30 inches) hanging from the upper jaw, and 14 to 35 ventral pleats extending from the lower jaw to the navel, or even beyond. The blow from the two blowholes is low and bushy and may appear v-shaped.
The head is covered with fleshy tubercles, each with at least one stiff hair. The lower jaw is also covered with fleshy tubercles and has a rounded protuberance near the tip.
Natural History
Humpback whales are found in all the oceans of the world. They undertake long seasonal migrations from productive high-latitude feeding grounds – sometimes following close to the coast or along the continental shelf – to traditional low-latitude breeding grounds, often clustered around insulated coasts or offshore reef systems. Some animals may over-winter in the feeding grounds.
Mating and calving take place in the winter; the whales may not feed during this time. In the North Atlantic, distinct populations of humpback whales occur on separate feeding grounds in areas such as the Gulf of Maine, off eastern Canada and western Greenland, Iceland and Norway, but mix on common breeding grounds in the Caribbean.
In the North Pacific, the humpback whales that feed in Alaska migrate to the Hawaiian Islands while those in the California stock breed in coastal Mexican waters.
Less is known about the movements of Southern Hemisphere humpback whales that feed in the Southern Ocean, but there are breeding populations around Madagascar and eastern Africa, western South America, Australia, and South Pacific islands and reef systems.
Males and females reach sexual maturity at about four to eight years of age. One calf is born every two to three years after an 11 – 12 month gestation period. Calves are weaned at 10 – 12 months.
Male humpback whales are known for their complex "songs." These songs can be heard during the breeding season; they may include many different frequencies, are unique to the different populations, and may last up to 20 minutes before being repeated. Humpbacks live to about 50 years.
Like the other Balaenopterids, humpbacks are fast and active lunge-feeders. As they take in large quantities of water and prey (krill and small schooling fish such as capelin, mackerel, sand lance, and herring), their throat grooves expand. When the mouth is closed the water is expelled, leaving the prey on the inside of the baleen plates.
Humpbacks may feed alone or cooperatively. Some use a unique technique called "bubble feeding, in which a curtain of bubbles from the blowhole is used to trap certain prey types. Humpbacks may also feed by herding prey and feeding in formation with others.
Energetic displays including "spyhopping" (lifting their heads vertically out of the water), "lobtailing" and "flippering (slapping their tails or flippers on the surface), as well as "breaching" (throwing their bodies out of the water). These behaviors make humpbacks one of the favorites of whale watchers. They can also be inquisitive and will sometimes approach boats.
Some populations of humpback whales have been studied in detail; scientists have been observing the same individuals over many years. In other areas, very little is known about this species.
Some of the populations that were reduced by whaling to very small numbers appear to be recovering. Others have shown little evidence of recovery.
Situation De L'Espèce
StatusToday the humpback whale is listed as Vulnerable by the International Union for the Conservation of Nature and Natural Resources (IUCN). The species is also listed on Appendix I of the United Nations Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES).
Threats to the Species
Due to their tendency to aggregate near the shore
in tropical breeding grounds and polar feeding grounds, humpback whales were an
easy target for early whalers.
It is thought that as much as 95 percent
of the pre-exploitation population was eliminated.
Commercial whaling of
humpbacks officially stopped in 1966, although some aboriginal hunts still
occasionally take place. Today, the same coastal habits that made them an easy
target for whalers make them prone to entanglement in fishing gear, collisions
with ships, and noise pollution.
International Trade
Listed on
CITES Appendix I, which prohibits
trade.
Auteur Et Sources
SourcesCITES. 2001. Balaenoptera edeni. www.cites.org.
Clapham, Phillip J. 2000. The humpback whale: seasonal feeding and breeding in the baleen whale, In Cetacean Societies: Field studies of dolphins and whales, Mann, J., R.C. Connor, P.L. Tyack and H. Whitehead (Eds.). The University of Chicago Press, Chicago. 433pp.
IUCN. 2001. The 2000 IUCN Red List of Threatened Species. www.redlist.org.
Jefferson, T.A., S. Leatherwood and M.A. Webber. 1993. Marine mammals of the world. FAO Species Identification Guide. UNEP, Rome. 320pp.
Marine Mammal Center. 1997. Humpback whale. http://www.tmmc.org/humpback.htm.
Alaska Department of Fish &Game. 2000. Humpback whale. www.state.ak.us.
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