The narwhal (Monodon monoceros), is a species of toothed whale, and the only member of the genus Monodon. Its closest living relative is the beluga whale, and cases of interbreeding between the two species have been recorded. It is sexually dimorphic, as adult males are larger than females and have a long single tusk that can be up to 3 m (9.8 ft). The narwhal has a mottled pigmentation, with blackish-brown markings over a white background. It has a short dorsal ridge in place of a dorsal fin, which is thought to facilitate movement under the ice, or reduce surface area and heat loss. An adult narwhal is typically 3.0 to 5.5 m (9.8 to 18.0 ft) in length and 800 to 1,600 kg (1,800 to 3,500 lb) in weight. Carl Linnaeus scientifically described the species in his 1758 work Systema Naturae.
The narwhal inhabits arctic waters of Canada, Greenland and Russia. Every year, it migrates to ice-free summering grounds, usually in shallow waters and exhibit a high fidelity of return to the same grounds. In spite of its carnivorous nature, it is susceptible to attacks by polar bears, orcas and humans. Its primary food sources include polar and Arctic cod, Greenland halibut, cuttlefish, shrimp, and armhook squid. The narwhal is one of the deepest-diving marine mammals, with many individuals reaching depths of over 1,500 m (5,000 ft) in their search for prey. Social creatures, narwhals congregate in groups of up to 20 individuals. They mate in the offshore pack ice in April or May, and have a gestation lasting an average of 15 months. Like most other cetaceans, the narwhal uses clicks, whistles and knocks to communicate with others of its kind.
The narwhal was one of many species originally described by Carl Linnaeus in his 1758 Systema Naturae.[5] An early 1555 drawing by Olaus Magnus depicts a fish-like creature with a horn on its forehead; Magnus later assigned it to "Monocerote".[6] Its name comes from the Old Norse word nár, meaning 'corpse', which possibly refers to the animal's grey, mottled skin[7] and its habit of remaining motionless at the water's surface, a behaviour known as "logging" that usually happens in the summer.[8] The scientific name, Monodon monoceros, is derived from Greek: 'single-tooth single-horn'.[9]
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.[10][11]
Although the narwhal and beluga are classified as separate genera, there is some evidence that they may, very rarely, interbreed. The remains of an abnormal-looking whale, described by marine zoologists as unlike any known species, were found in West Greenland around 1990. It had features midway between a narwhal and a beluga, indicating that the remains belonged to a narluga (a hybrid between the two species);[12] this was confirmed by a 2019 DNA analysis.[13] Whether the hybrid could breed remains unknown.[14][12]
Evolution
Genetic evidence suggests that within the Delphinoidea clade, porpoises are more closely related to the white whales, and these two families constitute a separate clade which diverged from dolphins within the last 11 million years.[15] 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.[16] A 2020 phylogenetic study based on genome sequencing suggested that, around 4.98 million years ago (mya), the narwhal split from the beluga whale.[17] 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.[18] The following phylogenetic tree is based on a 2019 study of the family Monodontidae.[19]
The narwhal is an agile and medium-sized whale. Adult males are around 4.1 m (13 ft) long from nose to tail tip, and females average 3.5 m (11 ft); the overall body length of 3.0 to 5.5 m (9.8 to 18.0 ft) is suggested for both males and females. Adults typically range between 800 and 1,600 kg (1,800 and 3,500 lb), with males outweighing their female counterparts.[20][21] Male narwhals attain sexual maturity at 11 to 13 years of age, reaching a length of 3.9 m (13 ft). Females become sexually mature at a younger age, between 5 and 8 years old, when they are about 3.4 m (11 ft) long.[22]
The pigmentation of the narwhal is a mottled pattern, with blackish-brown markings over a white background.[7] At sexual maturity, white patches grow on the navel and genital slit. The skin is light grey at birth, and darkens over time. Old narwhals on the other hand, may be almost pure white.[20][23] Narwhals do not have a dorsal fin; they instead possess 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.[24] Like land mammals, the narwhal's neck vertebrae are jointed, instead of being fused together as in most whales; this allows a great range of neck flexibility. These characteristics—a dorsal ridge and jointed neck vertebrae—are shared by the beluga whale.[8] Male and female narwhals have different tail flukes; the former are bent inward, while the latter have a sweep-back on the front margins. This is thought to be an adaptation for reducing drag caused by the tusk.[21]
Compared with most other marine mammals, the narwhal has a higher amount of myoglobin in its body, facilitating deeper dives.[25] Its skeletal muscle is adapted to withstand prolonged periods of deep-sea foraging. During such activities, oxygen is reserved in the muscles, which are typically slow-twitch, allowing for endurance and manoeuvrable motion.[26]
Tusk
Narwhal tusk
The most conspicuous characteristic of the male narwhal is a single long tusk, which is a canine tooth[27] that projects from the left side of the upper jaw.[28] The tusk grows throughout the animal's life, reaching an average of 1.5 to 2.5 m (4.9 to 8.2 ft), although they can sometimes reach lengths of up 3 m (9.8 ft).[29][30][31] The tusk is hollow and weighs up to 7.45 kg (16.4 lb). Some males may grow two tusks, occurring when the right canine also protrudes through the lip.[32] Females rarely grow tusks: when they do, the tusks are typically smaller than those of males, with less noticeable spirals.[33][34]
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. There is a scientific consensus that tusks are secondary sexual characteristics which indicate social status.[35] The tusk is a highly innervatedsensory organ with millions of nerve endings that connect seawater stimuli to the brain, allowing the narwhal to sense temperature variability in its surroundings.[36][37][38] According to a 2014 study, male narwhals may exchange information about the properties of the water they have travelled through by rubbing their tusks together, as opposed to the previously assumed posturing display of aggressive male-to-male rivalry.[27]Drone footage from August 2016 in Tremblay Sound, Nunavut, revealed that narwhals used their tusks to tap and stun small Arctic cod, making them easier to catch for feeding.[39][40] Females, who usually do not have tusks, live longer than males, hence the tusk cannot be essential to the animal's survival. It is generally accepted that the primary function of the narwhal tusk is associated with sexual selection.[41]
Vestigial teeth
The narwhal has several small vestigial teeth that reside in open tooth sockets in the upper jaw. These teeth, which differ in form and composition, encircle the exposed tooth sockets laterally, posteriorly, and ventrally.[27][42] The varied morphology and anatomy of small teeth indicate a path of evolutionary obsolescence.[27]
Distribution
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,[43][44] 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.[45]
Migration
Narwhals exhibit seasonal migration, 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 or in wider fractures known as leads.[46] As spring comes, these leads open up into channels and the narwhals return to the coastal bays.[47] Narwhals in Baffin Bay typically travel further north, to northern Canada and Greenland, between June and September. After this period, they travel about 1,700 kilometres (1,100 mi) south to the Davis Strait, and stay there until April.[45] During winter, narwhals from Canada and West Greenland regularly visit the pack ice of the Davis Strait and Baffin Bay along the continental slope which contains less than 5% open water and hosts high densities of Greenland halibut.[48]
Behaviour and ecology
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"); mixed groups can occur at any time of year.[20] In the summer, several groups come together, forming larger aggregations which can contain 500 to over 1,000 individuals.[20] Bull narwhals have been observed rubbing each other's tusks, a behaviour known as "tusking".[37][49]
When in their wintering waters, narwhals make some of the deepest dives recorded for marine mammals, 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.[50] Dive times can also vary in depth, based on season and local variation between environments. For example, in the Baffin Bay wintering grounds, narwhals 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 greater water depths in these areas. This is mainly attributed to prey being concentrated nearer to the surface, which causes narwhals to subsequently alter their foraging strategies.[50]
Diet
Compared with other marine mammals, narwhals have a relatively restricted and specialised diet.[51] 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.[52] A study of the stomach contents of 73 narwhals found that Arctic cod (Boreogadus saida) was the most commonly consumed prey, followed by Greenland halibut (Reinhardtius hippoglossoides). Large quantities of Boreo-Atlantic armhook squid (Gonatus fabricii) were discovered. Males were more likely than females to consume two additional prey species: polar cod (Arctogadus glacialis) and redfish (Sebastes marinus), both of which are mostly found in depths of more than 500 m (1,600 ft). The study also concluded that the size of prey did not differ among genders or ages.[53] Other items found in stomachs have included wolffish, capelin, skate eggs and sometimes rocks.[20][48][46]
Narwhal diet varies by season. In winter, narwhals feed on demersal prey, mostly flatfish, under dense pack ice. During the summer, they eat mostly Arctic cod and Greenland halibut, with other fish such as polar cod making up the remainder of their diet.[53] Narwhals consume much more food throughout the winter months than they do in summer.[48][46]
Breeding
Female narwhals start bearing calves when they are six to eight years old.[8] Adults mate from March to May when they are in offshore pack ice. After a gestation of 15 months, females give birth to calves between July and August.[54] As with most marine mammals, only a single young is born, averaging 1.5 m (4.9 ft) in length. At birth, calves are white or light grey in colour.[55] The birth interval is typically between two and three years.[22] Summer population surveys along different coastal inlets of Baffin Island, found that calf numbers varied from 0.05% of 35,000 in Admiralty Inlet, to 5% of 10,000 total in Eclipse Sound. These findings suggest that higher calf counts may reflect calving and nursery habitats in favourable inlets.[56]
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 about 20 months.[41] This long lactation period gives calves time to learn skills they will need to survive as they mature. Calves typically stay within two body lengths of the mother.[8][56]
The species goes through menopause; during this phase, females may continue to take care of calves in the pod.[22] A 2024 study concluded that five species of Odontoceti evolved menopause to acquire higher overall longevity, though their reproductive periods did not change. To explain this, scientists hypothesized that calves of the five Odontoceti species require the assistance of menopausal females for an enhanced chance at survival, as they are extremely difficult for a single female to successfully rear.[57]
Like most toothed whales, narwhals use sound to navigate and hunt for food. They primarily vocalise through clicks, whistles and knocks, created by air movement between chambers near the blowhole.[58] The frequency of these sounds ranges from 0.3 to 125 hertz, while those used for echolocation typically fall between 19 and 48 hertz.[59][60] Sounds are reflected off the sloping front of the skull and focused by the animal's melon, which can be controlled through surrounding musculature.[61] Echolocation clicks are used for detecting prey and locating barriers at short distances.[62] Whistles and throbs are most commonly used to communicate with other pod members.[63] Calls recorded from the same pod are more similar than calls from different pods, suggesting the possibility of group- or individual-specific calls. Narwhals sometimes adjust the duration and pitch of their pulsed calls to maximise sound propagation in varying acoustic environments.[64] Other sounds produced by narwhals include trumpeting and "squeaking-door sounds".[8] The narwhal vocal repertoire is similar to that of the beluga whale. They have comparable whistle frequency ranges, whistle duration and repetition rates of pulse calls, though beluga whistles are thought to have a higher frequency range and more diversified whistle contours.[65]
Narwhals live an average of 50 years, though techniques using amino acid dating from the lens of the eyes suggest that female narwhals can reach 115±10 years and male narwhals can live to 84±9 years.[66]
Death by suffocation often occurs when narwhals fail to migrate before the Arctic freezes over in late autumn.[20][67] Narwhals drown if open water is no longer accessible and ice is too thick for them to break through. Breathing holes in ice may be up to 1,450 m (4,760 ft) apart, which limits the use of foraging grounds. These holes must be at least 0.5 m (1.6 ft) wide to allow an adult whale to breathe.[25] Narwhals also die of starvation from entrapment events.[20]
In 1914–1915, around 600 narwhal carcasses were discovered after entrapment events, 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.[68] Several cases of sea entrapment were recorded in 2008–2010, during the Arctic winter, including in some places where such events had never been recorded before.[67] This suggests later departure dates from summering grounds. Wind and currents move sea ice from adjacent locations to Greenland, leading to fluctuations in concentration. 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 to what extent sea ice changes pose a danger to narwhals.[20]
Major predators are polar bears, which typically wait at breathing holes for young narwhals.[20][69]Orcas group together to overwhelm and surround narwhal pods,[70] killing up to dozens of narwhals in a single attack.[71] To escape predators such as orcas, narwhals may use prolonged submersion to hide under ice floes rather than relying on speed.[25]
In a 19-year study, researchers were able to detect Brucella in the blood streams of a large sample size of narwhals. They were also recorded with whale lice species such as cyamid monodontis and cyamid nodosus. Other pathogens include Toxoplasma gondi, morbillivirus, and papillomavirus.[72] In 2018, a female narwhal was recorded with alphaherpesvirus off the coast of Tremblay Sound.[73]
In the 1972 Marine Mammal Protection Act, the United States banned commercial imports of products made from narwhal body parts.[3] Narwhals are listed in Appendix II of CITES and CMS, meaning that trade of narwhals and their body parts is restricted and controlled internationally.[4][74] The species is also classified as endangered under COSEWIC.[45] Narwhals are difficult to keep in captivity.[37]
Threats
Beluga and narwhal catches
Narwhals are hunted for their skin, meat, teeth, tusks and carved vertebrae, which are commercially traded. About 1,000 narwhals are killed per year: 600 in Canada and 400 in Greenland. Canadian catches 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 caught more, 700–900 per year, in the 1980s and 1990s.[75]
Narwhal tusks are sold both carved and uncarved in Canada[76][77] and Greenland.[78] Per hunted narwhal, an average of one or two vertebrae and one or two teeth are sold.[76] In Greenland, the skin (muktuk) is sold commercially to fish factories,[78] and in Canada to other communities.[76] 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. The net income after subtracting costs in time and equipment, was a loss of CA$7 (US$6.80) per narwhal. Hunts receive subsidies, but they continue mainly to support tradition, rather than for profit. Economic analysis noted that whale watching may be an alternate source of revenue.[76]
As narwhals grow, bioaccumulation of heavy metals take place.[79] 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.[80] When bioaccumulating, numerous metals appear in the blubber, liver, kidney and musculature. A study found that the blubber was nearly devoid of these metals, whereas the liver and kidneys had a dense concentration of them. Relative to the liver, the kidney has a greater concentration of zinc and cadmium, while lead, copper and mercury were not nearly as abundant. Individuals of different weight and sex showed dissimilarities in the concentration of metals in their organs.[81]
Narwhals are one of the Arctic marine mammals most vulnerable to climate change[47] due to sea ice decline, 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.[82] It is thought that narwhals' foraging ranges reflect patterns they acquired early in life, which improves their capacity to obtain the food supplies they need for the winter. This strategy focuses on strong site fidelity rather than individual-level responses to local prey distribution, resulting in focal foraging areas during the winter. As such, despite changing conditions, narwhals will continue to return to the same areas during migration.[82] As narwhals emerged during the late Pliocene epoch, they must have undergone adaptation to glacials and climate change.[83]
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 enhanced endeavour,[84] implying that climate change may be making the narwhal more vulnerable to hunting. Scientists recommend assessing population numbers, assigning sustainable quotas, and ensuring local acceptance of sustainable development. Seismic surveys associated with oil exploration disrupt the narwhal's normal migration patterns. These disturbed migrations may also be associated with increased sea ice entrapment.[85]
Relationship with humans
Inuit
Hunter posing next to a narwhal head (1903)The head of an Inuit lance made from a narwhal tusk, with a meteorite-iron point (British Museum)
Narwhals are internationally protected and hunting one is illegal. However, Inuit are permitted to hunt narwhals for subsistence. Narwhals are very difficult to encroach and present challenging targets for hunters.[86] 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. As a custom, one or two vertebrae per animal are used for tools and art.[76][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 spiralling narwhal tusk.[87]
Tusk trade
The narwhal tusk has been highly sought-after in Europe for centuries. This stems from a medieval belief that narwhal tusks were the horns of the legendary unicorn.[88][89] Trade of narwhal tusks began approximately in 1000.[90] Scientists have long speculated that Vikings collected tusks washed ashore on beaches of Greenland and surrounding areas, yet others theorised Norsemen interchanged tusks with Europeans after acquiring them from Inuit. Tusks then spread across the Middle East and East Asia. A hypothesis suggested that Norsemen may have hunted narwhals, though this was never confirmed and was later disproven.[91][92] Vikings made weapons out of tusks to be used in battles or hunts. The trade became prevalent in Renaissance times.[93]
Across medieval Europe, narwhal tusks were given as state gifts to kings and queens. There was also a growing demand for the supposed powers of unicorn horns.[88] In the 1700s to 1800s, the price tag of tusks were said to be a couple of hundred times greater than its weight in gold.[94]Ivan the Terrible had a jewellery-covered narwhal tusk on his deathbed,[88] while Elizabeth I received a narwhal tusk said to be worth £10,000 pounds sterling[95] from the privateerMartin Frobisher, who proposed that the tusk was from a "sea-unicorne". The tusks were displayed in cabinets of curiosities.[96][97] They were also used as antidotes, and to detect poison.[98] The tusk has been used for therapeutic purposes, including cleansing polluted water and treating rubella, measles, fevers, and pain.[99][100] The rise of science towards the end of the 17th century led to a decreased belief in magic and alchemy. After it was determined that narwhal tusks were not effective antidotes, the practice of using them for this purpose was subsequently abandoned.[101]
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