bowhead whale

bowhead whale

bowhead whale: see right whale.
The Bowhead Whale (Balaena mysticetus), also known as Greenland Right Whale or Arctic Whale, is a baleen whale of the right whale family Balaenidae. A stocky dark-colored whale without a dorsal fin, it can grow to 20 meters (66 ft) in length. Estimated maximum weight of this thick-bodied species is 136 tonnes (152 tons), second only to the Blue Whale, although the Bowhead lags behind several other whales in maximum length. The Bowhead spends all of its life in fertile Arctic waters, unlike other whales that migrate for feeding or reproduction.

The Bowhead was an early target for the whaling industry, and its population was severely depleted before a whaling moratorium was introduced in 1966. The population is estimated to be over 11,700 worldwide, down from an estimated 50,000 before the commencement of whaling.

Taxonomy

The Bowhead Whale was described by Carl 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 and the right whales. Thus, it is likely that all four species will be placed in one genus in some future review.

It is thought that Balaena 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.

Description

The Bowhead Whale is a robust-bodied, dark-colored animal 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. This whale has a massive bony skulls which it uses to break the ice from beneath to breathe. Some Inuit hunters have reported whales surfacing through of ice in this method. The Bowhead may reach lengths of up to and females are larger than males. The blubber layer of whale flesh is thicker than in any other animal, averaging . The longest reported length for a Bowhead, was for an unweighed giant caught off of Spitsbergen, Norway.

Distribution

The Bowhead Whale is the only baleen whale that spends its entire life in and around Arctic waters. Those found off Alaska spend the winter months in the southwestern Bering Sea. It migrates northward in the spring, following openings in the pack ice, into the Chukchi and Beaufort seas, hunting zooplankton such as copepods. The Bowhead is a slow swimmer and usually travels alone or in small herds of up to six animals. Although it may stay below the water surface for as long as forty minutes in a single dive, it is not thought to be a deep diver.

Reproduction and lifespan

The Bowhead Whale is highly vocal and uses underwater sounds to communicate while traveling, feeding, and socializing. Some Bowheads make long repetitive songs that may be mating displays. The whales' behavior can also include breaching, tail slapping, and spyhopping. 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 long and approximately , growing to 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, 1999, and 2007 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).

In May 2007, a 50 ton specimen caught and harvested off the Alaskan coast was discovered to have the head of an explosive harpoon embedded deep under the blubber of its neck. Examination determined the 3 1/2 inch arrow-shaped projectile was manufactured in New Bedford, Massachusetts, a major whaling center, around 1890. This proof that it survived a similar hunt more than a century ago indicated to researchers that the whale's age was between 115 and 130 years old.

Because of their possible lifespans, female Bowhead Whales are believed to go through menopause. Observations of very large animals without calves support this hypothesis.

Population status

The Bowhead Whale has been hunted for its blubber, meat, oil, bones, and baleen. It is closely related to the right whales and shares with them 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 began in the 16th century, when the Basques hunted Bowhead Whales migrating south through the Strait of Belle Isle in the fall and early winter. In 1611, the first whaling expedition was sent to Spitsbergen, and by mid-century the population(s) there had practically been wiped out, forcing whalers to begin voyaging into the "West Ice" - the pack ice off the east coast of Greenland. By 1719, whalers had reached the Davis Strait, and by the first quarter of the 19th century Baffin Bay. In the North Pacific, commercial whaling began in the 1840s, 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 10,500 animals (2001). The status of the other Bowhead populations is less well known. There are about 1,200 Bowheads off West Greenland (2006), while the Spitsbergen Bowhead population may only number in the tens.

In March, 2008, Canada's Department of Fisheries and Oceans stated that previous estimates of the Bowhead population in the Eastern Arctic had undercounted the number of whales in the region, with a new estimate of 14,400 animals (r. 4,800-43,000). These larger numbers would correspond to the estimates of the whale population before whaling, indicating that this population has recovered.

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:

Behavior and predators

Unlike most other baleen whales which primarily feed on concentrated shoals of prey species, the Bowhead Whale feeds in a manner similar to the Basking Shark by swimming forward with its mouths agape and continuously filtering water through its baleen plates. Thus, it specializes in feeding on much smaller prey items such as copepods. Its mouth with the large upturning lip on the lower jaw helps to reinforce and contain the baleen plates within its mouth, and prevents buckling or breakage of the plates due to the pressure of the water passing through them as it swims forward. This is in contrast to the rorquals which have distendable ventral pleats that they fill with water containing prey, which is then pushed out and filtered through the baleen plates in distinct batches.

The Bowhead is social and nonaggressive, and will retreat under the ice when threatened. Its only predators are humans and the Orca. On rare occasions, the Bowheads are also attacked by sea lions.

References

See also

External links

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