Like the Beluga whale, narwhals are medium-sized whales. For both sexes, excluding the male's tusk, the total body size can range from ; the males are slightly larger than the females. The average weight of an adult narwhal is . At around 11 to 13 years old, the males become sexually mature; females become sexually mature at about 5 to 8 years old. Narwhals do not have a dorsal fin, and their neck vertebrae are jointed like those of other mammals, not fused as in dolphins and most whales.
Found primarily in Northern Canada and Greenlandic and Russian waters, the narwhal is a uniquely specialized Arctic predator. In winter, it feeds on benthic prey, mostly flatfish, under dense pack ice. During the summer, narwhals mostly eat Arctic cod and Greenland halibut, with other fish such as polar cod making up the remainder of their diet. Each year, they migrate from bays into the ocean as summer comes. In the winter, the male narwhals occasionally dive up to in depth, with dives lasting up to 25 minutes. Narwhals, like most toothed whales, communicate with "clicks", "whistles", and "knocks".
Narwhals can live up to 50 years. They are often killed by suffocation when the sea ice freezes over. Another cause of fatality, specifically among young whales, is starvation. The current population of the narwhal is about 75,000, so narwhals qualify for Near Threatened under the criterion of the International Union for Conservation of Nature (IUCN). Narwhals have been harvested for over a thousand years by Inuit people in northern Canada and Greenland for whale meat and ivory, and a regulated subsistence hunt continues.
The narwhal is most closely related to the beluga whale. Together, these two species comprise the only extant members of the family Monodontidae, sometimes referred to as the "white whales". The Monodontidae are distinguished by medium size (at around in length), forehead melons (round sensory organs), short snouts, and the absence of a true dorsal fin. ξ2 Although the narwhal and the beluga are classified as separate genera, with one species each, there is some evidence that they may, very rarely, interbreed. The complete skull of an anomalous whale was discovered in West Greenland circa 1990. It was described by marine zoologists as unlike any known species, but with features midway between a narwhal and a beluga, consistent with the hypothesis that the anomalous whale was a narwhal-beluga hybrid.
The white whales, (Delphinidae) and (Phocoenidae) together comprise the superfamily Delphinoidea, which are of likely monophyletic origin. Genetic evidence suggests the porpoises are more closely related to the white whales, and that these two families constitute a separate clade which diverged from the rest of Delphinoidea within the past 11 million years. Fossil evidence shows that ancient white whales lived in tropical waters. They may have migrated to Arctic and sub-Arctic waters in response to changes in the marine food chain during the Pliocene.
The pigmentation of narwhals is a mottled pattern, with blackish-brown markings over a white background. They are darkest when born and become whiter with age; white patches develop on the navel and genital slit at sexual maturity. Old males may be almost pure white. Narwhals do not have a dorsal fin, possibly an evolutionary adaptation to swimming easily under ice. Their neck vertebrae are jointed, like those of land mammals, instead of being fused together as in most whales. Both these characteristics are shared by the beluga whale. The tail flukes of female narwhals have front edges that are swept back, and those of males have front edges that are more concave and lack a sweep-back. This is thought to be an adaptation for reducing drag caused by the tusk.
The tusk is an sensory organ with millions of patent nerve endings connecting seawater stimuli in the external ocean environment with the brain. The rubbing of tusks together which males engage in is now hypothesized to communicate information about the water each has traveled through rather than to represent the previously assumed “male-to-male rivalry“. Narwhals have only occasionally been observed using the tusk for aggressive behavior.
At times, a bull narwhal may rub its tusk with another bull, a display known as "tusking" and thought to maintain social dominance hierarchies. However, this behaviour may exhibit tusk use as a sensory and communication organ for sharing information about water chemistry sensed in tusk microchannels.
Narwhals have a very intense summer feeding society. One study published in the Canadian Journal of Zoology tested 73 narwhals of different age and gender to see what they ate. The individuals were from the Pond Inlet and had their stomach contents tested from June 1978 until September 1979. The study found in 1978 that the Arctic cod ( Boreogadus saida) made up about 51% of the diet of the narwhals, with the next most common animal being the Greenland halibut ( Reinhardtius hippoglossoides), consisting of 37% of the weight of their diet. A year later, the percentages of both animals in the diet of narwhals had changed. Arctic cod represented 57%, and Greenland halibut 29% in 1979. The deep-water fish - halibut, redfish ( Sebastes marinus), and polar cod ( Arctogadus glacialis) - are found in the diet of the males, which means that the narwhals can dive deeper than below sea level. The study found that the dietary needs of the narwhal did not differ among genders or ages.
Newborn calves begin their lives with a thin layer of blubber which thickens as they nurse their mother's milk which is rich in fat. Calves are dependent on milk for around 20 months. This long lactation period gives calves time to learn skills needed for survival during maturation when they stay within two body lengths of the mother.
Mortality often occurs when the narwhals suffocate after they fail to leave before the surface of the Arctic waters freeze over in the late autumn. Open water is formed in ice-covered water by fracturing events induced by strong winds, but when these conditions are absent ice can quickly form. The last major entrapment events occurred when there was little to no wind. Narwhals are mammals and need air to breathe, so when open water is no longer accessible and the ice is too thick for them to break through, they can drown. Maximum Oxygen swimming distance between breathing holes in ice is less than which limits the use of foraging grounds and these holes must be at least wide to allow an adult whale to breathe. The events can trap groups as large as 600 individuals. Most entrapment events occur in narwhal wintering areas such as Disko Bay. In the largest entrapment in 1915 in West Greenland, over 1,000 narwhals were trapped under the ice.
Despite the decreases in sea ice cover, there were several large cases of sea ice entrapment in 2008–2010 in the winter close to known summering grounds, two of which were locations where there had been no previous cases documented. This suggests later departure dates from summering grounds. Sites surrounding Greenland experience advection (moving) of sea ice from surrounding regions by wind and currents, increasing the variability of sea ice concentration. Due to strong site fidelity, changes in weather and ice conditions are not always associated with narwhal movement toward open water and therefore more data is needed to determine how vulnerable narwhals are to future sea ice changes. Narwhals can also die of starvation, especially the young.
During growth, the narwhal accumulates metals in its internal organs. One study found that many metals are low in concentration in the blubber of narwhals, and high in the liver and the kidney. Zinc and cadmium are found in higher densities in the kidney than the liver, and lead, copper and mercury were found to be the opposite. Certain metals were correlated with size and sex. During growth, it was found that mercury accumulated in the liver, kidney, muscle and blubber, and that cadmium settled in the blubber.
Narwhals are one of the most vulnerable Arctic marine mammals to climate change due to altering sea ice coverage in their environment, especially in their northern wintering grounds such as the Baffin Bay and Davis Strait regions. Satellite data collected from these areas shows the amount of sea ice has been markedly reduced. Narwhals' ranges for foraging are believed to be patterns developed early in their life which increase their ability to gain necessary food resources during winter. This strategy focuses on strong philopatry rather than individual level responses to local prey distribution and this results in focal foraging areas during the winter. As such, despite changing conditions narwhals will continue returning to the same areas during migration. Despite its vulnerability to sea ice change, the narwhal has some flexibility when it comes to sea ice and habitat selection. It evolved in the late Pliocene, and so is moderately accustomed to periods of glaciation and environmental variability.
An indirect danger for narwhals associated with changes in sea ice is the increased exposure in open water. In 2002 there was an increase in narwhal catches by hunters in Siorapaluk that did not appear to be associated with increased effort, implying that climate change may be making the narwhal more vulnerable to harvesting. Scientists urge assessment of population numbers with the assignment of sustainable catch share for stocks and the collaboration of management agreements to ensure local acceptance. Seismic surveys associated with oil exploration have also disrupted normal migration patterns which may also be associated with increased sea ice entrapment.
Some Middle Ages Europeans believed narwhal tusks to be the horns from the legendary unicorn.Daston, Lorraine and Park, Katharine (2001). Wonders and the Order of Nature, 1150–1750. New York: Zone Books, ISBN 0-942299-91-4. As these horns were considered to have magic powers, such as neutralising poison and curing melancholia, Vikings and other northern traders were able to sell them for many times their weight in gold. The tusks were used to make cups that were thought to negate any poison that may have been slipped into the drink. In 1555, Olaus Magnus published a drawing of a fish-like creature with a horn on its forehead, correctly identifying it as a "Narwal". ξ6 During the 16th century, Queen Elizabeth I received a carved and bejewelled narwhal tusk worth 10,000 —the cost of a castle (approximately £1.5–2.5 million in 2007, using the retail price index) from Sir Humphrey Gilbert, who proposed the tusk was from a "sea-unicorne". The tusks were staples of the cabinet of curiosities. European knowledge of the tusk's origin developed gradually during the Age of Exploration, as explorers and naturalists began to visit Arctic regions themselves.
Herman Melville wrote a section on the narwhal (written as "narwhale") in his 1851 novel Moby-Dick, in which he claims a narwhal tusk hung for "a long period" in Windsor Castle after Sir Martin Frobisher had given it to Queen Elizabeth. Another claim he made was that the Danish kings made their thrones from narwhal tusks.
The narwhal is largely mentioned in the book Lore of the Unicorn. In the book, the author Odell Shepard describes the earlier interpretations of the narwhal, from being a fish with a horn in its forehead, to a sea-unicorn. Shepard tells that from the Danish and Dutch, the world was told of the importance of both narwhals and their tusks, and how they had lived for at least 200 years until being discovered by the explorers. Later, after the narwhal had been identified, two tusks were presented to the King of Denmark. One of these tusks was apparently long, and was then transported to a region then known as Nova Zembla.
==Gallery==
Tusk and vestigial teeth
Vestigial teeth
Distribution
Migration
Behaviour
Diet
Diving
Communication
Breeding and early life
Life span and mortality
Conservation issues
Cultural depictions
In legend
In literature and art
Further reading
External links
References
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