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 a single case of
interbreeding between the two species has been recorded. It is
sexually dimorphic, as adult males are larger and have a single
tusk that can be up to 3 m (9.8 ft) long. Several theories have been proposed for the function of the narwhal tusk, including its use in fights, in feeding or in
sexual selection. 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 has a body length of 3.0 to 5.5 m (9.8 to 18.0 ft) and weighs 800 to 1,600 kg (1,800 to 3,500 lb).
The narwhal inhabits
Arctic waters of Canada, Greenland and Russia. Every year, it
migrates to ice-free summering grounds, usually in shallow waters, and often
returns to the same sites in subsequent years. Its diet mainly consists of
polar and
Arctic cod,
Greenland halibut,
cuttlefish,
shrimp, and
armhook squid. It is one of the deepest-diving
cetaceans, 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 from March to May, and have a
gestation lasting an average of 15 months. Like most other cetaceans, the narwhal uses clicks, whistles and knocks to communicate.
The narwhal was scientifically described by
Carl Linnaeus in his 1758
Systema Naturae.[5] One of the earliest illustrations of the species is a 1555 drawing by
Olaus Magnus depicting a fish-like creature with a horn on its forehead; Magnus later called it "Monocerote".[6] The word "narwhal" comes from the
Old Norsenárhval, meaning 'corpse whale', which possibly refers to the animal's grey, mottled skin[7][8] and its habit of remaining motionless when at the water's surface, a behaviour known as "logging" that usually happens in the summer.[9] The scientific name, Monodon monoceros, is derived from
Greek: 'single-tooth single-horn'.[10]
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.[11][12]
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);[13] this was confirmed by a 2019 DNA analysis.[14] Whether the hybrid
could breed remains unknown.[15][13]
The following
phylogenetic tree is based on a 2019 study of the family Monodontidae.[16]
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.[17] 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.[18] A 2020
phylogenetic study based on
mitochondrial DNA suggested that, around 4.98
million years ago (mya), the narwhal split from the beluga whale.[19] 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.[20]
Several extinct toothed whale species have been identified, including multiple close relatives of narwhals. Casatia is one of the earliest narwhal ancestors from the
early Pliocene (5.1–4.5 mya). The genus contains a single species, C. thermophila that was described from a partial skull. Fossils were discovered in Italy and are the first and only fossils of a
monodontid from the
Mediterranean Basin known.[16]Bohaskaia and Haborodelphis are other extinct genera known during the early Pliocene of eastern United States, and the north-west Pacific.[18][21]
Description
Narwhals near the surface
Illustration of a narwhal
The narwhal is an agile 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 females.[22][23] 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.[24]
The
pigmentation of the narwhal is a
mottled pattern, with blackish-brown markings over a white background.[8] 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.[22][25] 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.[26] 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.[9] 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.[23]
Compared with most other marine mammals, the narwhal has a higher amount of
myoglobin in its body, facilitating deeper dives.[27] 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.[28]
Tusk
Narwhal tusk
The most conspicuous characteristic of the male narwhal is a single long tusk, which is a
canine tooth[29] that projects from the left side of the upper jaw.[30] The tusk grows throughout the animal's life, reaching an average of 1.5 to 2.5 m (4.9 to 8.2 ft), and a maximum of 3 m (9.8 ft).[31][32][33] 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 protrudes through the lip.[34] Females rarely grow tusks: when they do, the tusks are typically smaller than those of males, with less noticeable spirals.[35][36]
The purpose of the narwhal tusk is debated. Some biologists suggest that narwhals use their tusks in fights, while others argue that they may be of use in feeding. There is, however, a
scientific consensus that tusks are
secondary sexual characteristics which indicate social status.[37] 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.[38] Their tusks are also able to pick up the slightest increase or decrease in the magnitude of particles and water pressure.[7][39] 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.[29]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.[40][41] 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.[42]
Vestigial teeth
The narwhal has a single pair of 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.[29][43] Vestigial teeth in male narwhals are commonly shed in the
palate. The varied morphology and anatomy of small teeth indicate a path of evolutionary obsolescence. Limited research on vestigial teeth indicate that they serve no function.[29][44]
Distribution
Pod of narwhals
The narwhal is found in the Atlantic and Russian areas of the
Arctic Ocean. Individuals are commonly recorded in the
Canadian Arctic Archipelago,[45][46] 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.[8] The northernmost sightings of narwhals have occurred north of Franz Joseph Land, at about
85° north.[8] There are an estimated 12,500 narwhals in northern Hudson Bay, whereas around 140,000 reside in Baffin Bay.[47]
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.[48] As spring comes, these leads open up into channels and the narwhals return to the coastal
bays.[49] 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.[47] 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.[50]
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.[22] In the summer, several groups come together, forming larger aggregations which can contain 500 to over 1,000 individuals.[22] Bull narwhals have been observed rubbing each other's tusks, a behaviour known as "tusking".[7][51]
When in their wintering waters, narwhals make some of the deepest dives recorded for cetaceans, diving to at least 800 m (2,620 ft) over 15 times per day, with many dives reaching 1,500 m (4,920 ft).[52][53] Dives to these depths last around 25 minutes. 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 alter their foraging strategies.[52]
Diet
Compared with other marine mammals, narwhals have a relatively restricted and specialised diet.[54] Due to the lack of well-developed
dentition, narwhals are believed to feed by swimming close to prey and sucking them into the mouth.[55] 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 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.[56] Other items found in stomachs have included
wolffish,
capelin,
skate eggs and sometimes rocks.[22][50][48]
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.[56] Narwhals consume more food in the winter months than they do in summer.[50][48]
Breeding
Most female narwhals reproduce by the time they are six to eight years old.[9]Courtship and
mating behaviour for the species has been recorded from March to May, when they are in offshore pack ice, and is thought to involve dominant males mating with several partners. The average
gestation lasts 15 months; births appear to be most frequent between July and August. A female has a birth interval of around 2–3 years.[24][57][58] As with most marine mammals, only a single young is born, averaging 1.5 m (4.9 ft) in length with white or light grey pigmentation.[59] 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.[60]
Newborn calves begin their lives with a thin layer of
blubber. The blubber thickens as they
nurse their mother's milk, which is rich in fat. Calves are dependent on milk for about 20 months.[42] 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.[9][60]
Narwhals are among the few animals that undergo
menopause and live for decades after they have finished breeding. Females in this phase may continue protecting calves in the pod.[24] 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 hypothesised 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.[61]
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.[62] The frequency of these sounds ranges from 0.3 to 125
hertz, while those used for
echolocation typically fall between 19 and 48 hertz.[63][64] Sounds are reflected off the sloping front of the skull and focused by the animal's
melon, which can be controlled through surrounding musculature.[65] Echolocation clicks are used for detecting prey and locating barriers at short distances.[66] Whistles and throbs are most commonly used to communicate with other pod members.[67] 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.[68][69] Other sounds produced by narwhals include trumpeting and "squeaking-door sounds".[9] The narwhal vocal repertoire is similar to that of the beluga whale. However, the frequency ranges, durations, and repetition rates of narwhal clicks differ from those of belugas.[70]
Age determination techniques using the number of
periosteum layers in the
lower jaw reveal that 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.[71]
Death by
suffocation often occurs when narwhals fail to migrate before the
Arctic freezes over in late autumn. This is known as an "entrapment event".[22][72] 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.[27] Narwhals also die of
starvation from entrapment events.[22]
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.[73] 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.[72] 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.[22]
Predators include
polar bears, which have been recorded waiting at breathing holes for young narwhals.[22][74]Orcas group together to overwhelm and surround narwhal pods,[75] sometimes killing several individuals in a single attack.[76] To escape predators such as orcas, narwhals may use prolonged submersion to hide under
ice floes rather than relying on speed.[27]
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.[81]
Narwhal tusks are sold both carved and uncarved in Canada[82][83] and Greenland.[84] Per hunted narwhal, an average of one or two vertebrae and one or two teeth are sold.[82] In Greenland, the skin (muktuk) is sold commercially to
fish factories,[84] and in Canada to other communities.[82] 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.[82]
As narwhals grow,
bioaccumulation of heavy metals take place.[85] 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.[86] 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.[87]
Narwhals are one of the Arctic marine mammals most vulnerable to
climate change[49] 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.[88] 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.[88] As narwhals emerged during the
late Pliocene epoch, they must have undergone adaptation to
glacials and climate change.[89]
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,[90] 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.[91]
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)
For millennia,
Inuit have relied on narwhals for subsistence.[92] This species has 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.[82][8] 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.[8]
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.[93]
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.[94][95] Trade of narwhal tusks began approximately in 1000.[96] Scientists have long speculated that
Vikings collected tusks washed ashore on beaches of Greenland and surrounding areas, yet others theorised
Norsemen traded tusks with Europeans after acquiring them from Inuit. The trade later found its way into the markets of the
Middle East and
East Asia. A hypothesis suggested that Norsemen may have hunted narwhals, though this was never confirmed and was later disproven.[97][98] The trade became prevalent in
Renaissance times.[99]
Across medieval Europe, narwhal tusks were given as state gifts to kings and queens. During this time, a growing demand for the supposed powers of unicorn horns emerged.[94] 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.[100]Ivan the Terrible had a jewellery-covered narwhal tusk on his deathbed,[94] while
Elizabeth I received a narwhal tusk said to be worth £10,000
pounds sterling[101] from the
privateerMartin Frobisher, who proposed that the tusk was from a "sea-unicorne". Both items were displayed in
cabinets of curiosities.[102][103] Europeans also had a belief that narwhal tusks could serve as antidotes and detect poison, as well as treat conditions and illnesses such as
rubella,
measles,
fevers, and
pain.[104][105][106] 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 unicorn horns, the practice of using them for magical purposes was abandoned.[107][108]
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