Bowhead whale
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| Balaena mysticetus Linnaeus, 1758 |
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 Bowhead whale range
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The bowhead whale (Balaena mysticetus), also known as Greenland Right Whale or Arctic Whale, is a marine mammal of the order Cetacea. It can grow to 20 metres (66 ft), long.
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[edit] Description
Bowhead whales are robust-bodied, dark-coloured animals with no dorsal fin and a strongly bowed lower jaw and narrow upper jaw. The baleen plates, exceeding three meters and the longest of the baleen whales, are used to strain tiny prey from the water. The whales have massive bony skulls which they use to break from beneath the ice to breathe. Some Inuit hunters have reported whales surfacing through 60 cm (2 ft) of ice in this method. Bowheads may reach lengths of up to 20 metres and females are larger than males. The blubber layer of whale flesh is thicker than in any other animal, averaging 43–50 cm (17–20 in).
[edit] Taxonomy
- See also: Evolution of cetaceans
The bowhead whale was described by Carolus Linnaeus in the 10th edition of his Systema Naturae (1758). Balaena has remained a monotypic genus ever since. Leiobalaena, described by Eschricht in 1849, is a junior synonym.
The bowhead whale is an individual species, separate from the other Right Whales. It has always been recognized as such, and stands alone in its own genus as it has done since the work of Gray in 1821. There is, however, little genetic evidence to support this two-genera view. Indeed, scientists see greater differences between the members of Balaenoptera than between the bowhead whale and the right whales. Thus, it is likely that all four species will be placed in one genus in some future review[2].
It is thought that Balena prisca, one of the five Balaena fossils from the late Miocene (~10 mya) to early Pleistocene (~1.5 mya), may be the same as the modern bowhead whale. Prior to these there is a long gap back to the next related cetacean in the fossil record, Morenocetus, which was found in a South American deposit dating back 23 million years.
[edit] Distribution
Bowhead whales are the only baleen whales that spend their entire lives in and around Arctic waters. The bowhead whales found off Alaska spend the winter months in the southwestern Bering Sea. They migrate northward in the spring, following openings in the pack ice, into the Chukchi and Beaufort seas, hunting krill and zooplankton. Bowheads are slow swimmers and usually travel alone or in small herds of up to six animals. Although they may stay below the water surface for as long as forty minutes in a single dive, they are not thought to be deep divers.
[edit] Reproduction and lifespan
Bowhead whales are highly vocal and use underwater sounds to communicate while traveling, feeding, and socializing. Some bowheads make long repetitive songs that may be mating displays. The whales behaviour can also include breaching, tail slapping, and spy-hopping. Sexual activity occurs between pairs and in boisterous groups of several males and one or two females.
Breeding has been observed from March through August; conception is believed to occur primarily in March. Reproduction can begin when a whale is 10 to 15 years old. Females produce a calf once every 3 to 4 years, after a 13 to 14 month pregnancy. The newborn calf is about 4.5 m long and approximately 1000 kg (2,200 lb), growing to 9 m by its first birthday. The lifespan of a bowhead was once thought to be 60 to 70 years, similar to other whales. However, discoveries of antique ivory spear points in living whales in 1993, 1995 and 1999 have triggered further research based on structures in the whale's eye, leading to the reliable conclusion that at least some individuals have lived to be 150–200 years old (another report has said a female at the age of 90 was allegedly still reproductive). [3] Because of their possible life span, female bowhead whales are believed to go through menopause. Observations of very large animals without calves support this hypothesis.[4]
[edit] Population status
Bowhead whales have been killed for their blubber, meat, oil, bones and baleen. Century-old harpoons have been found embedded in some whales' blubber, showing how old they can get and how they were attacked. They are closely related to the right whale and share with it the hunting-ideal characteristics of slow swimming and floating after death. Before commercial whaling, there were over 50,000 bowhead whales in the north polar region (estimated). Commercial whaling starting in 1611 near Svalbard and Greenland and wiped out herds of the slow-growing whales, and then moved on to new areas. In the North Pacific, the commercial whaling began in the mid-1800s, and within two decades over 60 percent of the bowhead whale population had been wiped out.
Commercial whaling, the principal cause of the population decline, has been discontinued. The population off Alaska has increased since commercial whaling ceased. Alaska Natives continue to kill small numbers of bowhead whales in subsistence hunts each year. This level of killing (25–40 animals annually) is not expected to affect the population's recovery. The bowhead whale population off Alaska's coast (also called the Bering-Chukchi-Beaufort stock) appears to be recovering but remains at about 7,800 animals (1990), roughly 41 percent of the pre-whaling population. The status of the other bowhead populations is less well known. These stocks are thought to be very small, probably in the low hundreds, for a possible worldwide population of 8,000–9,200 individuals.
The bowhead is listed in Appendix I by CITES (that is, "threatened with extinction"). It is listed as endangered under the auspices of the United States' Endangered Species Act. The IUCN Red List data is as follows:
- Spitzbergen population - Critically endangered
- Sea of Okhotsk subpopulation - Endangered
- Baffin Bay-Davis Strait stock - Endangered
- Hudson Bay-Foxe Basin stock - Vulnerable
- Bering-Chukchi-Beaufort stock - Lower risk - conservation dependent
[edit] Range, behaviour, and predators
The bowhead spends all of its life in fertile Arctic waters, unlike other whales that migrate for feeding or reproduction. Bowheads are social and nonaggressive, and will retreat under the ice when threatened. Their only predators are humans and orcas.
[edit] See also
[edit] References
- ^ Cetacean Specialist Group (1996). Balaena mysticetus. 2006 IUCN Red List of Threatened Species. IUCN 2006. Retrieved on 06 May 2006. Database entry includes a lengthy justification of why this species is dependent on conservation
- ^ Kenney, Robert D. (2002). “North Atlantic, North Pacific and Southern Right Whales”, William F. Perrin, Bernd Wursig and J. G. M. Thewissen: The Encyclopedia of Marine Mammals. Academic Press, 806-813. ISBN 0-12-551340-2.
- ^ Bowhead Whales May Be the World's Oldest Mammals
- ^ Rare Whales Can Live to Nearly 200, Eye Tissue Reveals
[edit] External links
