Narwhal

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Narwhal[1]
Size comparison with an average human
Conservation status
Scientific classification
Kingdom:Animalia
Phylum:Chordata
Class:Mammalia
Order:Cetacea
Suborder:Odontoceti
Family:Monodontidae
Genus:Monodon
Linnaeus, 1758
Species:M. monoceros
Binomial name
Monodon monoceros
Linnaeus, 1758
Narwhal range (in blue)
 
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Narwhal[1]
Size comparison with an average human
Conservation status
Scientific classification
Kingdom:Animalia
Phylum:Chordata
Class:Mammalia
Order:Cetacea
Suborder:Odontoceti
Family:Monodontidae
Genus:Monodon
Linnaeus, 1758
Species:M. monoceros
Binomial name
Monodon monoceros
Linnaeus, 1758
Narwhal range (in blue)

The narwhal, or narwhale, (Monodon monoceros) is a medium-sized toothed whale that lives year-round in the Arctic. One of two living species of whale in the Monodontidae family, along with the beluga whale, narwhal males are distinguished by a long, straight, helical tusk, actually an elongated upper left canine. Found primarily in Canadian Arctic and Greenlandic waters, rarely south of 65°N latitude, the narwhal is a uniquely specialized Arctic predator. In the winter, it feeds on benthic prey, mostly flatfish, at depths of up to 1500 m under dense pack ice.[3] Narwhals have been harvested for over a thousand years by Inuit people in northern Canada and Greenland for meat and ivory, and a regulated subsistence hunt continues to this day. While populations appear stable, the narwhal is particularly vulnerable to climate change due to a narrow geographical range and specialized diet.[4]

Taxonomy and etymology

The narwhal was one of the many species originally described by Linnaeus in his Systema Naturae.[5] Its name is derived from the Old Norse word nár, meaning "corpse", in reference to the animal's greyish, mottled pigmentation, like that of a drowned sailor[6] and its summer-time habit of laying inactive at or near the surface of the sea (called "logging").[7] The scientific name, Monodon monoceros, is derived from Greek: "one-tooth one-horn"[6] or "one-toothed unicorn".

The narwhal is most closely related to the beluga whale. Together, these two species comprise the only extant members of the Monodontidae family, sometimes referred to as the "white whales". The Monodontidae are distinguished by medium size (at around 4 m (13 ft) in length), forehead melons, short snouts, and the absence of a true dorsal fin.[8] The white whales, dolphins (Delphinidae) and porpoises (Phocoenidae) together comprise the Delphinoidea superfamily, 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 Delphinoidea within the past 11 million years.[9]

Description

This narwhal skull has double tusks, a rare trait in narwhals. Usually, males have a single long tusk, the canine on the left side of the upper jaw. (Zoologisches Museum in Hamburg)

These are medium-sized whales, being around the same size as a beluga whale. Total length in both sexes, excluding the "tusk" of the male, can range from 3.95 to 5.5 m (13 to 18 ft).[10] Males, at an average length of 4.1 m (13 ft 5 in), are slightly larger than females, at an average of 3.5 m (11 ft 6 in). Typical adult body weight can range from 800 to 1,600 kg (1,800 to 3,500 lb).[10] Males attain sexual maturity at 11 to 13 years of age, when they are approximately 3.9 m (12 ft 10 in) long, and females attain maturity at 5 to 8 years old, when they are 3.4 m (11 ft 2 in) long.[10] The pigmentation of the narwhal is a mottled pattern, with blackish-brown markings over a white background. They are darkest when born and become whiter in color with age, with white patches developing on the navel and genital slit at sexual maturity. Old males may be almost pure white.[6][10][11] Narwhals do not have a dorsal fin, possibly an evolutionary adaptation to swimming easily under ice. In addition, the neck vertebrae of the narwhal are not fused together, but are jointed, like those of land mammals. Both these characteristics are shared by the beluga whale (Delphinapterus leucas), a fellow inhabitant of icy Arctic seas.[7]

The most conspicuous characteristic of the male narwhal is its single extremely long tusk, a canine tooth[12] that projects from the left side of the upper jaw, through the lip and forms a left-handed helix. The tusk grows throughout life reaching lengths from 1.5 to 3.1 m (4 ft 11 in to 10 ft 2 in). Despite its formidable appearance, the tusk is hollow and weighs only around 10 kg (22 lb). About one in 500 males has two tusks, which occurs when the right canine, normally small and less straight, also grows out through the lip. Females may grow tusks sometimes, although the evidence on the frequency of this is somewhat conflicting. It has been stated that only about 15 percent of females have a tusk[13] and that "When the occasional female narwhal grows a tusk, the female narwhal tusk tends to be much smaller than the male narwhal tusk, with a less pronounced spiral."[14]. Elsewhere, it has been stated that "In most females the teeth never erupt through the gum"[15] and "Female narwhals have a shorter, and straighter tusk" but with no comment on the frequency of occurrence.[16] Females may produce a second tusk, but there is only a single recorded case of a female with dual tusks.[17]

Biology considers the tusk a secondary sexual characteristic, similar to the mane of a lion or the tail feathers of a peacock.[6] Charles Darwin discussed and defended this hypothesis at length in The Descent of Man, and Selection in Relation to Sex (1871). It may help determine social rank, maintain dominance hierarchies, or help young males develop skills necessary for performance in adult sexual roles. Narwhals have rarely been observed using their tusk for fighting,[18] other aggressive behavior or for breaking sea ice in their Arctic habitat.[6] Some narwhals have a second, small tooth in their mouths, but are essentially toothless.[10] The tusk is a highly innervated sensory organ, as scientists finally established in the early years of the 21st century after many centuries of myth and fiction ascribing it other roles, ranging from magical to weaponry.[19] There is at least one known instance where a tusk was used against another species. The broken tip of a narwhal tusk was found embedded in the melon of a beluga, indicating there was an aggressive encounter.[7]

Distribution

The frequent (solid) and rare (striped) occurrence of narwhal populations

The narwhal is found predominantly in the Atlantic and Russian areas of the Arctic Ocean. Individuals are commonly recorded in the northern part of Hudson Bay, Hudson Strait, Baffin Bay; off the east coast of Greenland; and in a strip running east from the northern end of Greenland round to eastern Russia (170° East). Land in this strip includes Svalbard, Franz Joseph Land, and Severnaya Zemlya.[6] The northernmost sightings of narwhal have occurred north of Franz Joseph Land, at about 85° North latitude.[6] Most of the world's narwhals are concentrated in the fjords and inlets of Northern Canada and western Greenland.



Behavior and diet

Narwhals have a relatively restricted and specialized diet. Their prey is predominantly composed of Greenland halibut, polar and Arctic cod, cuttlefish, shrimp and armhook squid. Additional items found in stomachs have included wolffish, capelin, skate eggs and sometimes rocks, accidentally ingested when whales feed near the bottom.[3][10][20][21] Due to the lack of well-developed dentition in the mouth, narwhals are believed to feed by swimming towards prey until it is within close range and then sucking it with considerable force into the mouth. It is thought that the beaked whales, who have similarly reduced dentition, also suck up their prey.[22]

Narwhals are a migratory species. As spring comes, these leads open up into channels and the narwhals return to the coastal bays.[4]

Narwhals exhibit seasonal migrations, with a high fidelity of return to preferred, ice-free summering grounds, usually in shallow waters. In summer months, they move closer to coasts, usually in pods of 10–100. In the winter, they move to offshore, deeper waters under thick pack ice, surfacing in narrow fissures in the sea ice, or leads.[21] Narwhals from Canada and West Greenland winter regularly in the pack ice of Davis Strait and Baffin Bay along the continental slope with less than 5% open water and high densities of Greenland halibut.[3] Feeding in the winter accounts for a much larger portion of narwhal energy intake than in the summer[3][21] and, as marine predators, they are unique in their successful exploitation of deep-water arctic ecosystems.

Most notable of their adaptations is the ability to perform deep dives. When on their wintering grounds, the narwhals make some of the deepest dives ever recorded for a marine mammal, diving to at least 800 meters (2,625 feet) over 15 times per day, with many dives reaching 1,500 meters (4,921 feet). Dives to these depths last around 25 minutes, including the time spent at the bottom and the transit down and back from the surface.[23] In the shallower summering grounds, narwhals dive to depths between 30 and 300 meters (90–900 feet).

Narwhals "tusking"

Narwhals normally congregate in groups of about five to ten individuals, sometimes up to 20 outside the summer. Groups may be "nurseries" with only females and young or can contain only post-dispersal juveniles or adult males ("bulls"), though mixed groups can occur at any time of the year.[10] In the summer, several groups come together, forming larger aggregations. Such aggregations can contain from 500 to over 1000 individuals.[10] At times, bull narwhals rub their tusks together in an activity called "tusking".[20] This behavior is thought to maintain social dominance hierarchies[20] or maintenance of the tusk as a sensitive sensory organ.[19]

Narwhals have evolved complex and sophisticated systems using sound to investigate their environment and to find food. The narwhal can create "clicks", "whistles" and "knocks", probably by controlling air between chambers near the blowhole, as is known to be done in other odontocete species. These sounds may then be reflected off the sloping front of the skull. The sounds may then be further focused by the melon, the round space on the head filled with a mix of blubber oils, and can be altered in shape under muscular control. "Click trains" are used by toothed whales for echo-location of prey, and for detecting obstacles at short ranges. It has been suggested that individual "bangs" could be strong enough to disorient or incapacitate prey, making the prey easier to catch, but that idea has not been verified. Whistles are rarely heard. Trumpeting and squeaking door sounds may also be used for communication among narwhals.[7]

Breeding and early life

Females start bearing calves at six to eight years of age. Adult narwhals mate in April or May when they are in the offshore pack ice. Gestation lasts for 14 months and calves are born between June and August of the following year. Like most marine mammals, narwhals have only one calf at a time. Newborn calves average 1.6 metres in length and are dark grey. While the newborn calves have only a very thin layer of blubber, the mother’s milk is rich in fat and a thicker blubber layer soon develops in the calves. Calves are nursed about 20 months. The lengthy lactation period provides calves with time to learn the skills they need to survive. Mother and calf are usually close, and when the whales are traveling, the calf remains close to the mother’s back, where it may get assistance in swimming.[7]

Mortality and conservation

A polar bear scavenging a narwhal carcass
Narwhal tail fluke

Normally, narwhals can live quite a long life, with lifespans of up to at least 50 years recorded. Mortality often occurs when the narwhals suffocate after they fail to leave before the surface of the Arctic waters freeze over in the late fall.[10] Starvation can also threaten their lives, especially in young whales. Although almost all modern predation of narwhals is by humans, a few natural predators also attack them on occasion. The primary natural predators are polar bears, who attempt to swipe narwhals at breathing holes and mainly target young whales, a pod of killer whales (orcas) can overwhelm a single narwhal. Greenland sharks and walruses may take a few small young or weak and wounded adults, though this is likely quite rare.[10] Inuit people, who call a tusked narwhal "qilalugaq tugaalik", are allowed to hunt this whale species legally for subsistence. Narwhal has been extensively hunted the same way as other sea mammals, such as seals and whales, for its large quantities of fat which constituted one of the most important resources of the native people living in arctic regions. Almost all parts of the narwhal, meat, skin, blubber and organs are consumed. Mattak, the name for raw skin and blubber, is considered a delicacy, and the bones are used for tools and art.[6] The skin is an important source of vitamin C which is otherwise difficult to obtain. In some places in Greenland, such as Qaanaaq, traditional hunting methods are used, and whales are harpooned from handmade kayaks. In other parts of Greenland and Northern Canada, high-speed boats and hunting rifles are used.[6]

Narwhal have been found to be one of the most vulnerable arctic marine mammals to climate change. The study quantified the vulnerabilities of 11 year-round Arctic sea mammals.[4][24] Narwhals that have been brought into captivity tend to die of natural causes.[19] The world population of narwhals is currently estimated to be around 75,000.[4] Approximately 25,000–50,000 breeding narwhal are believed to exist in the wild worldwide.[10] The status of Narwhals is currently near threatened even though several sub-populations have evidence of decline. It is estimated that by 2017 they will reach threatened status.[citation needed] In an effort to support conservation actions for the whales, the European Union established an import ban on tusks. While there are many countries that have not only established these bans, they already have quotas on catches in place, which will be important also in newly opening areas caused by decreasing sea ice cover.[2]

Relation with humans

The head of a lance made from a Narwhal tusk with a meteorite iron blade

In Inuit legend, the narwhal's tusk was created when a woman with a harpoon rope tied around her waist was dragged into the ocean after the harpoon had struck a large narwhal. She was transformed into a narwhal herself, and her hair, which she was wearing in a twisted knot, became the characteristic spiral narwhal tusk.[25]

Image of narwhal from Brehms Tierleben

Some medieval Europeans believed narwhal tusks to be the horns from the legendary unicorn.[26] As these horns were considered to have magic powers, such as the ability to cure poison and 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. During the 16th century, Queen Elizabeth received a carved and bejeweled narwhal tusk for £10,000—the cost of a castle (approximately £1.5–2.5 million in 2007, using the retail price index).[27] The tusks were staples of the cabinet of curiosities.[28] The truth of the tusk's origin developed gradually during the Age of Exploration, as explorers and naturalists began to visit Arctic regions themselves. In 1555, Olaus Magnus published a drawing of a fish-like creature with a horn on its forehead, correctly identifying it as a "Narwal".[28] The narwhal was one of two possible explanations of the giant sea phenomenon written by Jules Verne in his book Twenty Thousand Leagues Under the Sea. The other possible explanation was a man-made vessel, but that was not likely in the opinion of the narrator.

Herman Melville wrote a section on the narwhal in 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.[29]

In 2013, Canadian artist Harley Valentine created the sculpture North Pole, a gold-polished, lost wax bronze cast of a seven foot, 100-year old narwhal tusk thought to have come from Grise Fiord in the Canadian Arctic. [30]

Climate change vulnerability

The extreme morphological and physiological traits which they adapted in order to allow them to reside in the harsh Arctic conditions may also limit their behavioral flexibility towards changing sea ice and temperature. Their tissue is composed largely of slow twitch oxidative muscle and contains one of the highest levels of Myoglobin in marine mammals; this provides significant endurance and helps them dive for about 15–24 minutes assuming they maintain their metabolic rate. They also possess specialized skeletal muscles that are geared towards allowing slow endurance swimming and prolonged diving behavior.[31] These muscles share similarities with the muscles used for running in human athletes. When it comes to escaping predators such as orcas, they typically choose prolonged submergence to hide under the ice rather than relying on speed. Since they are highly adapted through body morphology and skeletal muscle characteristics to the Arctic conditions, free-ranging narwhals may be reaching their physiological capacity in current environmental conditions.They are large in size which provides advantages in thermoregulation, however this can prove problematic when finding cracks in the ice large enough to allow them to breathe.[31]

Narwhals are long lived species which is beneficial for producing a few healthy offspring better fit for survival, but it also decreases their ability to respond to quickly changing environmental conditions since they reproduce at a much slower rate. Narwhal population size is considered small compared to original conditions resulting from centuries of heavy commercial and subsistence harvesting that the population has not been able to recover.[31]

Impact of sea ice change

One of the aspects that make narwhals vulnerable to climate change is the altering sea ice coverage in their environment, especially in their Northern wintering grounds such as the Baffin Bay and Davis Straitt regions. Satellite data collected from these areas shows the amount of sea ice has been markedly reduced.[32] In Baffin Bay there has been about a 9% sea ice decline per decade in the East.[33] This has been accompanied with earlier breakup of spring sea ice in Baffin Bay.[34] West Greenland ocean temperatures have been warming prominently since 2000 as a result of increased inflow from warmer waters from the Irminger Current into South and West Greenland.[35] The IPCC report predicts that the doubling of CO2 in the atmosphere will lead to the decline of 60% of the sea ice cover in the summer, which has the potential to alter production levels and alter the ecosystem.[36] Narwhal’s ranges for foraging are believed to be patterns developed early in their life which are intended to increase their ability to gain necessary food resources during winter stages. This strategy focuses on strong site fidelity rather individual level response to local prey distribution and this result in focal foraging areas during the winter so despite changing conditions Narwhals will continue returning to the same areas during migration.[32]

Another potential problem faced by narwhals is the risk of sea ice entrapment in their wintering grounds.[37] Open water is formed in ice-covered water by fracturing events that are induced by strong winds, however when these conditions are absent ice can quickly form. This correlates with the observations that the last major entrapment events occurred when there was little to no wind observed in the area. Since narwhals are mammals they 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 end up drowning. Maximum aerobic swimming distance between breathing holes in ice is less than 1,450 m which limits the use of foraging grounds and these holes must be at least 0.5 m wide to allow an adult whale to breathe.[31] The events can trap groups as large as 600 individuals. Most entrapment events occur in narwhal wintering areas such as Disko Bay and the largest entrapment event occurred in 1915 in West Greenland where over 1,000 narwhals were trapped under the ice.[38] Despite the decreases in Sea ice cover, there have been several large cases of sea ice entrapment in 2008–2010 that occurred in the winter but close to known summering grounds, two of which were locations where there had been no previous cases documented.[37] This suggests later departure dates from summering grounds, which were recorded to be moving toward late fall or even winter. Sites surrounding Greenland experience advection of sea ice from surrounding regions by wind and currents, which increased the variability of when sea ice concentration reached certain thresholds and at what date. Also, 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.

While temperature may be increasing, there are also microhabitat cases of sea ice increases in the arctic. These micro-habitats were found in Baffin Bay, Davis Strait, coastal West Greenland and Lancaster Sound.[39] While the cause of sea ice cooling in areas such as Baffin Bay is uncertain, it is most likely associated with changes in the thermohaline circulation, the North Atlantic Oscillation and the formation of sea ice bridge in Smith Sound.[40][41] This also plays a factor in increased sea ice entrapment vulnerability.

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.[42] Climate change therefore may be making them more vulnerable to harvesting. Scientists urge assessment of population numbers and the assignment of sustainable quotas for stocks of as well as the collaboration of management agreements to ensure local acceptance. Seismic surveys associated with oil exploration have also been noted to disrupt normal migration patterns which may also be associated with increased sea ice entrapment.[43]

See also

References

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Further reading

External links