Narwhal

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Narwhal[1]
Temporal range: Quaternary–Present
[2][3]
Diagram showing a narwhal and scuba diver from the side: the body of the whale is about three times longer than a human.
Size compared to an average human
CITES Appendix II (CITES)[5]
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Artiodactyla
Infraorder: Cetacea
Family: Monodontidae
Genus: Monodon
Linnaeus, 1758
Species:
M. monoceros
Binomial name
Monodon monoceros
The frequent (solid) and rare (striped) occurrence of narwhal populations

The narwhal (Monodon monoceros), is a species of toothed whale. It is a member of the family Monodontidae, and the only species in the genus Monodon. An adult narwhal is typically 3.5 to 5.5 m (11 to 18 ft) in length and 800 to 1,600 kg (1,800 to 3,500 lb) in weight. The most prominent feature of the species is an adult male's long single tusk that can be up to 3 m (9.8 ft). Instead of a dorsal fin, it possesses a shallow dorsal ridge. It is a social animal, and may associate in groups of up to 20 members. Carl Linnaeus scientifically described the species in 1758 in his work Systema Naturae.

It is mostly found in Arctic waters, and is only vulnerable to predatory attacks from polar bears and orcas. The narwhal typically visits the Baffin Bay, between June and September. After this period, it moves to Davis Strait, a journey that spans around 1,700 km (1,100 mi), and it stays there until April. Its prey mostly consists of  Arctogadus glacialis, Boreogadus saida, Greenland halibut, cuttlefish, shrimp, and armhook squid. The narwhal is one of the deepest-diving marine mammals, with many individuals diving at depths of over 1,500 m (5,000 ft). It mates in the offshore pack ice in April or May, and has a gestation lasting for an average of 15 months. Like most other cetaceans, the narwhal uses clicks, whistles and knocks to communicate with others of its kind.

There are estimated to be 170,000 living narwhals, and the species is listed as least concern by the International Union for Conservation of Nature. The narwhal has been harvested for hundreds of years by Inuit in northern Canada and Greenland for meat and ivory and a regulated subsistence hunt continues. The narwhal has been depicted in human culture since ancient times.

Taxonomy

The narwhal was one of many species originally described by Carl Linnaeus in his 1758 Systema Naturae.[6] Its name is derived from the Old Norse word nár, meaning "corpse", in reference to the animal's greyish, mottled pigmentation,[7] and its summertime habit of lying still at or near the surface of the sea (called "logging").[8] The scientific name, Monodon monoceros, is derived from Greek: "one-tooth one-horn".[7]

The narwhal is most closely related to the beluga whale (Delphinapterus leucas). 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 their pronounced melons (acoustic sensory organs), short snouts and the absence of a true dorsal fin.[9]

Although the narwhal and the beluga are classified as separate genera, there is some evidence that they may, very rarely, interbreed. The remains of three animals were discovered, including one of an abnormal-looking whale, in West Greenland around 1990. The unusual whale was described by marine zoologists as unlike any known species, and it had features midway between a narwhal and a beluga, indicating that the remains belonged to a narluga;[10] in 2019, this was confirmed by DNA analysis.[11] Whether the hybrid could breed remains unknown. It displayed unusual dentition suggesting that it hunted on the seabed, much as walruses do. This hunting technique is different from those of either parent species.[12][10]

Evolution

Genetic evidence suggests that within the Delphinoidea clade, porpoises are more closely related to the white whales and that these two families constitute a separate clade which diverged from dolphins within the past 11 million years.[13] Fossil evidence shows that ancient white whales lived in tropical waters. They may have migrated to Arctic and subarctic waters in response to changes in the marine food chain during the Pliocene.[14] A 2020 phylogenetic study based on genome sequencing suggested that, around 4.98 million years ago (mya), the narwhal split from the beluga whale.[15] Analysis of Monodontidae fossils indicates that they had separated from Phocoenidae around 10.82 to 20.12 mya; they are considered to be a sister taxon.[16] The following phylogenetic tree is based on a 2019 study of the family Monodontidae.[17]

Kentriodon pernix

Tursiops truncatus (Common bottlenose dolphin)

Phocoena phocoena (Harbour porpoise)

Monodontidae

Haborodelphis japonicus

Denebola brachycephala

Bohaskaia monodontoides

Monodon monoceros

Casatia thermophila

IRSNB M 1922

Delphinapterus leucas (Beluga whale)

Description

Two narwhals at the water surface
Narwhals near the surface

The narwhal is a medium-sized whale, with a body length of 3.5 to 5.5 m (11 to 18 ft), excluding the tusk.[18] Males average 4.1 m (13.5 ft) in length; females average 3.5 m (11.5 ft). It ranges in weight from 800 to 1,600 kg (1,760 to 3,530 lb), with males outweighing their female counterparts.[18] Male narwhals attain sexual maturity at 11 to 13 years of age, when they are typically 3.9 m (12.8 ft) long. Females become sexually mature at a younger age, between 5 and 8 years old, when they are about 3.4 m (11.2 ft) long.[18]

The pigmentation of the narwhal is a mottled pattern, with blackish-brown markings over a white background.[7] It is darkest when born and becomes paler with age; white patches develop on the navel and genital slit at sexual maturity. Old males may be almost pure white.[18][19] It does not have a dorsal fin; it instead possesses a shallow dorsal ridge. This is possibly an evolutionary adaptation to make swimming under ice easier, to facilitate rolling, or to reduce surface area and heat loss.[20] Its neck vertebrae are jointed, like those of land mammals, instead of being fused together as in most whales, allowing a great range of neck flexibility. These characteristics are shared by the closely related beluga whale.[8] The tail flukes of female narwhals have a sweep-back in the front edges and those of males lack such a characteristic; their tail flukes are curved inwards. This is thought to be an adaptation for reducing drag caused by the tusk.[21]

Compared to most other marine marines, the narwhal has a higher amount of myoglobin in its body, facilitating deeper dives.[22] Its skeletal muscle is designed to withstand prolonged periods of deep-sea foraging. During such activities, oxygen is reserved in the muscles, which are typically slow-twitched, allowing for slow yet maneuverable motion.[23]

Tusk

The tusk of a male narwhal on display.
Narwhal tusk

The most conspicuous characteristic of the male narwhal is a single long tusk, which is in fact a canine tooth[24] that projects from the left side of the upper jaw, through the lip and forms a left-handed helical spiral.[25] The tusk grows throughout the animal's life, reaching an average of 1.5 to 2.5 m (4.9 to 8.2 ft).[26][27] The maximum tusk length is 3 m (10 ft).[28] It is hollow and weighs up to 7.45 kg (16.4 lb). Some males may grow two tusks, occurring when the right canine also grows out through the lip.[29] Females rarely grow tusks: when they do, the tusks are typically smaller than those of males, with less noticeable spirals.[30][31]

The purpose of the narwhal tusk is debated. Some biologists suggest that narwhals use their tusks in fights, while others argue that their tusks may be of use in breaking sea ice or in finding food. However, there is a consensus that narwhal tusks are secondary sexual characteristics that are used to show social status.[32] The tusk is a highly innervated sensory organ with millions of nerve endings that connect seawater stimuli from the surrounding ocean environment to the brain, sensing temperature variability in the animal's surroundings.[33][34][35] In a 2014 paper, it was suggested that the rubbing of tusks together by male narwhals is a method of communicating information about characteristics of the water each has travelled through, rather than the previously assumed posturing display of aggressive male-to-male rivalry.[24] In August 2016, drone videos of narwhals surface-feeding in Tremblay Sound, Nunavut, showed that the tusk was used to tap and stun small Arctic cod, making them easier to catch for feeding.[36][37] The tusk cannot serve a critical function for the animal's survival, as females—which generally do not have tusks—typically live longer than males. Therefore, it is generally accepted that the primary function of the narwhal tusk is for reproduction.[38]

Vestigial teeth

The narwhal's mouth is toothless; it instead has several small vestigial teeth that mainly reside in open tooth sockets which are situated in the upper jaw. These teeth surround the open tooth sockets posteriorly, ventrally and laterally, and vary in shape and material.[24][39] The varied morphology and anatomy of small teeth indicate a path of evolutionary obsolescence.[24]

Distribution

Six narwhals near the water surface
Pod of narwhals

The narwhal is found predominantly in the Atlantic and Russian areas of the Arctic Ocean. Individuals are commonly recorded in the Canadian Arctic Archipelago,[40][41] such as 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.[7] The northernmost sightings of narwhals have occurred north of Franz Joseph Land, at about 85° North latitude.[7] There are an estimated 12,500 narwhals in northern Hudson Bay, whereas around 140,000 reside in Baffin Bay.[42]

Migration

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, often 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 in wider fractures known as leads.[43] As spring comes, these leads open up into channels and the narwhals return to the coastal bays.[44] Narwhals typically travel further north, to the Baffin Bay between June and September. After this period, they move south to Davis Strait, a journey that spans around 1,700 kilometres (1,100 mi), and they stay there until April.[42] 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.[45]

Behaviour and ecology

Tail fluke of two narwhals
Narwhal tail fluke

Narwhals normally congregate in groups of five to ten—and sometimes up to twenty—individuals. Groups may be "nurseries" with only females and young, or can contain only post-dispersal juveniles or adult males ("bulls"), but mixed groups can occur at any time of year.[18] In the summer, several groups come together, forming larger aggregations which can contain from 500 to over 1,000 individuals.[18] Bull narwhals have been observed rubbing each other's tusks, a display known as "tusking".[34][46]

When in their wintering waters, narwhals make some of the deepest dives recorded for a marine mammal, diving to at least 800 m (2,620 ft) over 15 times per day, with many dives reaching 1,500 m (4,920 ft). Dives to these depths last around 25 minutes.[47] Dive times can also vary in time and depth, based on local variation between environments, as well as seasonality. For example, in the Baffin Bay wintering grounds, they tend to dive deep within the precipitous coasts, typically south of Baffin Bay. This suggests differences in habitat structure, prey availability, or genetic adaptations between subpopulations. In the northern wintering grounds, narwhals do not dive as deep as the southern population, in spite of the fact that water depths in these areas are typically deeper. This is mainly attributed to prey being concentrated nearer the surface, which then causes narwhals to subsequently alter their foraging strategies.[47]

Diet

Compared to other marine mammals, narwhals have a relatively restricted and specialized diet.[48] A study of the stomach contents of 73 narwhals found that the Arctic cod (Boreogadus saida) and Greenland halibut (Reinhardtius hippoglossoides) were the most commonly consumed prey. Large quantities of Boreo-Atlantic armhook squid (Gonatus fabricii) were discovered, but this feeding likely occurred outside the summer. Males consumed two additional prey species—the redfish (Sebastes marinus) and polar cod (Arctogadus glacialis)—more frequently than females; both species are predominantly found in depths deeper than 500 m (1,640 ft). The study also concluded that the size of prey did not differ among genders or ages.[49] Other items found in stomachs have included wolffish, capelin, skate eggs and sometimes rocks.[18][45][43]

In winter, they feed on demersal prey, mostly flatfish, under dense pack ice. During the summer, narwhals eat mostly Arctic cod and Greenland halibut, with other fish such as polar cod making up the remainder of their diet.[49] Narwhals consume much more food throughout the winter months than they do during the summer months.[45][43] Due to the lack of well-developed dentition, narwhals are believed to feed by swimming close to prey and then sucking it into the mouth.[50]

Breeding

Females start bearing calves when six to eight years old.[8] Adult narwhals mate from March to May when they are in the offshore pack ice. After a gestation of 15 months, females give birth to calves between July and August.[51] As with most marine mammals, only a single young is born, averaging 1.5 m (4.9 ft) in length and white or light grey in colour.[52] The birth interval is typically between two and three years.[53] During summer population counts along different coastal inlets of Baffin Island, calf numbers varied from 0.05% to 5% of the total numbering from 10,000 to 35,000 narwhals, indicating that higher calf counts may reflect calving and nursery habitats in favourable inlets.[54]

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.[8] This long lactation period gives the calves time to learn skills they will need to survive as they mature. Calves typically stay within two body lengths of the mother.[8][54] The species is thought to go through menopause; during this phase, females may continue to take care of calves in the pod.[53]

Communication

Like most toothed whales, narwhals use sound to navigate and hunt for food. Narwhals primarily vocalise through "clicks", "whistles" and "knocks", created by air movement between chambers near the blow-hole.[55] The frequency of these sounds ranges from 0.3 to 125 hertz, while those used for echolocation typically falls between 19 and 48 hertz.[56][57] The sounds are reflected off the sloping front of the skull and focused by the animal's melon, which can be controlled through surrounding musculature.[58] Echolocation clicks are primarily produced for prey detection and for locating obstacles at short distances.[59] "Whistles" and "throbs" are mostly used to communicate with other pod members.[60] Calls recorded from the same pod are more similar than calls from different pods, suggesting the possibility of group- or individual-specific calls in narwhals. Narwhals sometimes adjust the duration and pitch of their pulsed calls to maximise sound propagation in varying acoustic environments.[61] Other sounds produced by narwhals include trumpeting and "squeaking-door sounds".[8] The narwhal vocal repertoire is similar to that of the closely related beluga, with comparable whistle frequency ranges, whistle duration and repetition rates of pulse calls, however beluga whistles are thought to have a higher frequency range and more diversified whistle contours.[62]

Lifespan and mortality

Polar feeding/scavenging on a dead narwhal
A polar bear scavenging a narwhal carcass

Narwhals live an average of 50 years, however, age determination techniques using amino acid dating from the lens of the eyes suggests that female narwhals can live to be as old as 115 ± 10 years and male narwhals for 84 ± 9 years.[63] Death by suffocation often occurs when narwhals fail to migrate before the Arctic freeze over in late autumn.[18][64] As narwhals breathe air, they drown if open water is no longer accessible and the ice is too thick for them to break through. Breathing holes in the ice may be up to 1,450 m (4,760 ft) apart, which limits the use of foraging grounds and these holes must be at least 0.5 m (1.6 ft) wide to allow an adult whale to breathe.[22] Narwhals also die of starvation from these entrapment events.[18]

In 1914–1915, entrapment affected around 600 individuals, most occurring in areas such as Disko Bay. In the largest entrapment in 1915 in West Greenland, over 1,000 narwhals were trapped under the ice.[65] Several cases of sea entrapment were recorded in 2008–2010, during the Arctic winter, including in some places where such events have never been recorded.[64] This suggests later departure dates from summering grounds. Sites surrounding Greenland experience advection (moving) of sea ice from surrounding regions caused by wind and currents, promoting changes in sea ice concentration in the process. Due to their tendency of returning to the same areas, changes in weather and ice conditions are not always associated with narwhal movement toward open water. It is currently unclear how far sea ice changes pose a danger to narwhals.[18]

Major predators are polar bears, which typically wait at breathing holes for young narwhals.[18][66] Orcas group together to overwhelm and surround narwhal pods,[67] in one case killing dozens of narwhals in a single attack.[68] To escape predators such as orcas, narwhals may use prolonged submergence to hide under ice floes rather than relying on speed.[22]

Conservation

The narwhal is listed as least concern on the IUCN Red List. As of 2017, the global population is estimated to be 123,000 mature individuals out of a total of 170,000. There are around 12,000 narwhals in Northern Hudson Bay, as of 2011, and around 49,000 in Somerset Island in 2013. There are approximately a total of 35,000 in Admiralty Inlet, 10,000 in Eclipse Sound, 17,000 in Eastern Baffin Bay, and 12,000 in Jones Sound. Population numbers in Smith Sound, Inglefield Bredning and Melville Bay are 16,000, 8,000 and 3,000, respectively. There are roughly 837 narwhals off the waters of Svalbard.[4]

In 1972, the United States banned commercial imports of products made from narwhal body parts as stated by the Marine Mammal Protection Act.[4] Narwhals are listed in Appendix II of CITES and CMS, meaning that trade of narwhals and their body parts is restricted and controlled internationally.[5][69] The species is also classified as endangered under COSEWIC.[42] Narwhals are difficult to keep in captivity.[34]

Threats

Data showing the number of caught belugas and narwhals
Beluga and narwhal catches

Humans hunt narwhals; narwhal products traded commercially include skin, meat, teeth and tusk, and carved vertebrae. About 1,000 narwhals are killed per year: 600 in Canada and 400 in Greenland. Canadian harvests were steady at this level in the 1970s, dropped to 300–400 per year in the late 1980s and 1990s and have risen again since 1999. Greenland harvested more, 700–900 per year, in the 1980s and 1990s.[70]

Tusks are sold both carved and uncarved in Canada[71][72] and Greenland.[73] An average of one or two vertebrae and one or two teeth per narwhal hunted are sold.[71] In Greenland the skin (muktuk) is sold commercially to fish factories,[73] and in Canada to other communities.[71] One estimate of the annual gross value received from narwhal hunts in Hudson Bay in 2013 was CA$6,500 (US$6,300) per narwhal, of which CA$4,570 (US$4,440) was for skin and meat. However the net income, after subtracting costs in time and equipment, was a loss of CA$7 (US$6.80) per person. Hunts receive subsidies, but they continue mainly to support tradition, rather than for the money and the economic analysis noted that whale watching may be an alternate source of revenue.[71]

A man holding the head of a dead narwhal
Hunter posing next to a narwhal head (1903)

As narwhals grow, bioaccumulation takes place.[74] It is thought that pollution in the ocean is the primary cause of bioaccumulation in marine mammals; this may lead to health problems for the narwhal population.[75] In this process numerous metals appear in the blubber, liver, kidney and musculature. Relative to the liver, the kidney has a greater concentration of zinc and cadmium. On the other hand, lead, copper and mercury were not nearly as abundant. A study found that the blubber was nearly devoid of these metals, whereas the liver and kidneys had a dense concentration of these metals. Individuals of different weight and sex showed dissimilarities in the concentration of metals in their organs.[74]

Narwhals are one of the most vulnerable Arctic marine mammals to climate change[44] 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 from what it was previously.[76] 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 site fidelity 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.[76] They emerged during the late Pliocene epoch and, therefore, must have undergone adaptation to glacials and climate change.[77]

Reduction in sea ice has possibly led to increased exposure to predation. In 2002, hunters in Siorapaluk experienced an increase in the number of caught narwhals, but this increase did not seem to be linked to increased effort,[78] implying that climate change may be making the narwhal more vulnerable to harvesting. Scientists recommend assessing population numbers, assigning sustainable quotas, and ensuring local acceptance of sustainable development. Seismic surveys associated with oil exploration disrupt the normal migration patterns. These disturbed migrations may also be associated with increased sea ice entrapment.[79]

Relationship with humans

Inuit

Inuit lance head with a meteorite-iron point made from narwhal tusk
The head of an Inuit lance with a meteorite-iron point made from a narwhal tusk (British Museum)

Inuit are able to hunt this whale species legally. They are extremely difficult to encroach, and make tricky catches for hunters.[80] Narwhals have been extensively hunted the same way as other sea mammals, such as seals and whales, for their large quantities of fat. Almost all parts of the narwhal; the meat, skin, blubber and organs are consumed. Muktuk, the raw skin and attached blubber, is considered a delicacy. One or two vertebrae per animal are used for tools and art.[71][7] The skin is an important source of vitamin C, which is otherwise difficult to obtain in the Arctic Circle. 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.[7]

In Inuit legend, the narwhal's tusk was created when a woman with harpoon rope tied around her waist was dragged into the ocean after the harpoon had stuck into a large narwhal. She was then transformed into a narwhal; her hair, which she was wearing in a twisted knot, became the spiraling narwhal tusk.[81]

European

The narwhal tusk has been a highly sought-after item in Europe for centuries. This stems from some medieval Europeans' belief of narwhal tusks being horns from the legendary unicorn.[82][83] Around 1,000 AD, Vikings collected tusks washed ashore in beaches of Greenland and surrounding areas, and traded them. Afterwards, they build weapons out of tusks to be used in battles or hunts. Hadley Meares, a historian, quoted "The trade strengthened during the Middle Ages, when the unicorn became a symbol of Christ, and therefore an almost holy animal". Ivan the Terrible had a jewelry-covered narwhal tusk on his deathbed.[84] The tusks were also used to make cups that were thought to detect any poison that may have been slipped into the drink.[85] In 1555, Olaus Magnus published a drawing of a fish-like creature with a horn on its forehead, correctly identifying it as a "Narwal".[86] During the 16th century, Elizabeth I received a narwhal tusk that was said to be worth 10,000 pounds sterling[87] from Martin Frobisher, an English sailor and privateer, who proposed that the tusk was from a "sea-unicorne". The tusks were displayed in many cabinets of curiosities.[88][89]

See also

References

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Further reading