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Monodon monocerosnarwhal

By Ann Dunford

Geographic Range

Monodon monoceros, commonly known as the narwhal, can be found in the Arctic and Atlantic Oceans. The narwhal is considered the northernmost cetacean and generally found between the latitudinal lines 70° and 80°N, and migrates seasonally. During the summer, narwhals are found in the northern Canadian Arctic, near the eastern shore of Greenland. In late September, most narwhal begin their southern migration to their winter home in Baffin Bay. The start of freezing or melting of the ice around the narwhal appears to signal these migrations. Although these are the commonly accepted homes of the narwhal, it is likely that they can be found elsewhere because it is uncommon to see them at the surface. (Heide-Jorgensen, et al., 2003; Laidre, et al., 2004; Lydersen, et al., 2007; Reeves and Tracey, 1980)

Habitat

The narwhal can be found in predominantly open, deep Arctic waters. The narwhal spends time in different depths of the water; while hunting narwhals tend to dive deeper and spend a longer amount of time underwater. However, during their migration narwhal dives tend to be shallower and more frequent. Maximum dives are about 900m. Both the summer and winter locations for the narwhal contain deep fjords. (Lydersen, et al., 2007; Reeves and Tracey, 1980)

  • Range depth
    0 to 900 m
    0.00 to 2952.76 ft

Physical Description

The narwhal is an easily recognized cetacean. Perhaps the most noticeable feature of the narwhal is the presence of a "tusk," which can grow to 3 m in length. The tusk is actually a canine tooth that protrudes out of the upper left lip in male narwhal. Narwhal have just two teeth; typically the left one erupts and the right tooth stays embedded. In most females both teeth stay embedded, however, it is possible for both sexes to exhibit one or two tusks. In the event of both tusks being present the left is always larger. All tusks spiral to the left, with a polished end and the rest of the horn being covered in algae.

Another unique physical characteristic is the lack of a dorsal fin. In place of a dorsal fin, narwhals have a dorsal ridge. The dorsal ridge and its notch pattern is unique, so it can be photographed and used to distinguish individual narwhal.

Another distinguishing characteristic is the change in narwhal coloration as they age. Narwhal are a dark blue-gray color at birth. As narwhals age, white begins to work into the dark color and create a mottled pattern. Adult narwhal have a dark mottled dorsal side and a cream colored ventral side. Old narwhal continue to get lighter and very old males can be mostly white in color.

Adult narwhals vary in length from 4 -5 m and range in weight from 900 - 1,600 kilograms. Newborn narwhals measure about 1.5 m in length and are usually around 80 kilograms. In a typical narwhal 30 - 35% of that weight is blubber. This layer of fat, ranging in thickness from 50 - 100 mm, is essential for the survival in Arctic waters. Narwhals can also be identified by their fins, which are smaller than those of most other cetaceans and have a distinctive tip that curls up. (Auger-Methe, et al., 2011; Nweeia, et al., 2012; Reeves and Tracey, 1980)

  • Range mass
    900 to 1600 kg
    1982.38 to 3524.23 lb
  • Range length
    4 to 5 m
    13.12 to 16.40 ft

Reproduction

The mating systems of narwhals are not known. (Reeves and Tracey, 1980)

It is assumed that narwhals reach sexual maturity at the same rate as their close relatives the beluga whale, Delphinapterus leucas. This would mean males reach maturity at eight to nine years for males and four to seven years for females. Narwhals are seasonal breeders and thought to mate between March and May while in their summer home. Following a fourteen month gestation they give birth the next June. The newborns are assumed to stay with their mother for at least the next twenty months of lactation, however, there are conflicting opinions on the exact duration of lactation. As a result of a long lactation period, female narwhals conceive every two to three years. Narwhals generally give birth to a single eighty kilogram offspring, although twins have been seen occasionally. Narwhal calves are born tail first and begin swimming shortly after birth. It is assumed that the protruding tooth in males is used by the females to judge the fitness of males, and thereby choose a mate. However, there are still conflicting opinions about the purpose of the tooth. (Klinowska, 1991; Marcoux, et al., 2012; Reeves and Tracey, 1980)

  • Breeding interval
    Narwhals conceive every two the three years.
  • Breeding season
    Narwhals breed between March and May.
  • Range number of offspring
    1 to 2
  • Average number of offspring
    1
  • Average number of offspring
    1
    AnAge
  • Average gestation period
    14 months
  • Average gestation period
    450 days
    AnAge
  • Average weaning age
    20 months
  • Average age at sexual or reproductive maturity (female)
    Sex: female
    2191 days
    AnAge
  • Average age at sexual or reproductive maturity (male)
    Sex: male
    2922 days
    AnAge

Gestation is thought to last about fourteen months in the narwhal, followed by twenty months of lactation.

Males are thought to have some parental investment, because males and females generally do not travel together, unless there is a calf with them. This is based on observations of traveling narwhals, however, whether the males provide food or protection for the offspring is not known.

Family association after weaning is also not known. Current studies are examining the relatedness of narwhals that live together, but no conclusions have been made yet. (Klinowska, 1991; Marcoux, et al., 2012; Reeves and Tracey, 1980)

Lifespan/Longevity

In the past the narwhals lifespan has been estimated by counting the growth rings on its unerupted tooth. However, after being reviewed by Hay (1980) this method does not seem accurate. If true, it would make their reproductive capabilities in a lifetime to equal twice that of the beluga whale, Delphinapterus leucas (the only other extant species in the family Monodontidae). It is generally accepted that narwhals live for about fifty years in the wild. Without an appropriate method of estimating age, this cannot be confirmed. The longest a narwhal has lived in captivity is four months, and the shortest is one month. Therefore, attempts at captivity have not been successful. (Hayssen, 1993; Klinowska, 1991)

Behavior

Narwhals are a highly social species, and are usually found in pods ranging from two to twenty-five members, with an average of 3.6 members. These pods become much larger while migrating as many pods merge into one large herd. In this case groups of several hundred members are possible. After migration, however, the whales return to their original smaller pods. Pods do not seem to follow a pattern of sex, age, or relatedness. Although it is widely accepted that the narwhal is a social species, details of their social structure are not known. Occasionally narwhal can get caught in savassat, or open areas surrounded by too much ice to allow the narwhal to escape. This usually results in the death of all the trapped animals either by predation or starvation. The whales have been seen using their heads to smash into the ice in an effort to break it. Unfortunately, this causes water to splash out of the hole, which freezes and reinforces their entrapment. There have also been observations of narwhals being extremely careful not to harm other members of its group with their tooth while stuck in a savassat. This observation confirms the narwhal’s gregarious nature and casts doubt on theories that the tooth is used as a weapon against other narwhals. Narwhals tend to be very inactive while they are at the surface. They have also been known to slowly sink when they sense vibrations from a ship. This paired with their coloration makes it hard to observe them. (Klinowska, 1991; Lydersen, et al., 2007; Marcoux, 2008; Marcoux, et al., 2012; Reeves and Tracey, 1980)

Home Range

The home range of narwhals is uncertain.

Communication and Perception

The narwhal communicates acoustically. This species has two different types of calls that it is able to produce. The first is categorized as a pulse; this type of call is typically between 12 and 20kHz. As the name suggests, this is a short burst of sound, or click, that is sent out frequently. These calls are likely used as a type of echolocation for the whale, allowing it to efficiently locate and catch prey. This type of call is also used for spatial orientation and likely helps the whales stay together while they are migrating.

The other type of acoustic call is the whistle. Unlike the pulsed call, whistles are longer calls with varying frequency and are likely used mainly for communication. These calls vary from 300Hz to 10kHz. Recent research has suggested that whistles can also be group specific, meaning that the calls of narwhals in one group are more similar to each other than they are to the calls of members of other groups. However, because of the challenges of understanding communication underwater in the wild, more specifics are not known about the possibility of a meaning behind narwhal whistles.

An examination of the tusk revealed about ten million nerve endings. This leads researchers to believe that the tusks have some sort of sensory function, but the specific function is not yet known. (Bobechko and Stockton, 2006; Marcoux, 2008; Marcoux, et al., 2012; Reeves and Tracey, 1980)

Food Habits

Studying the stomach contents of narwhal have shown that they have a very limited diet, and that it varies depending on the season. The first thing to note about narwhal diet is that they do not appear to feed during the summer. Examining the contents of the narwhal stomach during the other three seasons revealed the food the narwhal had recently ingested, however, during the summer months, no tissues were found in the stomach. Diet during the fall and winter consists of Greenland halibut, Reinhardtius hippoglossoides, and boreoatlantic armhook squid, Gonatus fabricii. During the spring narwhal eats polar cod, Boreogadus saida and Arctic cod, Arctogadus glacialis. These seasonal variations likely stem from the migration pattern of the narwhal. Crustaceans have also been found in narwhal stomachs, but fish and cephalopods are much more prevalent.

As a toothless whale, it is assumed that narwhals use suction to eat their prey. However, being an Arctic species that does not survive in captivity, this has not been tested.

There has also been speculation that the narwhal tusk is used for spearing prey, or that it can be used as an instrument to disturb the sediment at the bottom of the ocean and reveal prey. The likelihood of these two options is slim because tusks are most frequently found on males. If the tusk were an adaptation for food it would be found on all narwhal. (Laidre, et al., 2004; Marcoux, et al., 2012; Reeves and Tracey, 1980)

  • Animal Foods
  • fish
  • mollusks
  • aquatic crustaceans

Predation

Narwhals generally travel in small groups, and when being chased by a predator they have been seen getting closer together and traveling in a tighter group. This behavior has been seen in response to being chased by an orca, Orcinas orca, and when being chased by humans, Homo sapiens. One defense mechanism of the narwhal is their coloration, which acts as a type of camouflage in the ocean. Lighter coloration on the bottom helps them blend in with the sky when looking up from under them, and the darker, mottled color on their dorsal side blends in with the deep ocean below when looking down at them. The males are prized for their tusks, so when hunting occurs by humans, Homo sapiens, it is generally the adult males that are caught. This is thought to explain why adult males tend to stay farther offshore and spend less time at the surface than juveniles and females. This could be a possible adaptation to predation by humans, Homo sapiens. Narwhals have been found in the stomachs of Greenland sharks, Somniosus microcephalus, so it is assumed that narwhals are a part of their diet. Narwhals have also been eaten by walrus, Odobensus rosmarus, and polar bears, Ursus maritimus, however, predation by these two species only occurs when the narwhals are trapped in a savassat and have no way of escaping to open water. Although there are hypothesis that the tooth is used as a weapon to prevent predation, there is no evidence to support that theory. (Reeves and Tracey, 1980)

  • Anti-predator Adaptations
  • cryptic

Ecosystem Roles

Many endoparasites and ectoparasites use the narwhal as their host. The ecto-parasites include whale lice, Cyamus nodosus and Cyamus monodontis. They can be found in the tail notch, wounds, and in the skin surrounding the erupted tooth. The endoparasites include, but are not limited to the nematodes Porrocaecum decipiens, Anisaki simplex, Stenurus alatus, and Halocercus monoceris. Additional groups of parasites fall into the categories of trematodes, cestodes, and acanthocephalans. These endoparasites can be found throughout the body of the narwhal. Due to the narwhal's very limited diet, it is likely that their feeding patterns greatly influence the populations of their prey. However, because the narwhal is a migrating species it is not a constant predation pressure during migration. (Klinowska, 1991; Laidre and Heide-Jorgensen, 2005; Reeves and Tracey, 1980)

Commensal/Parasitic Species
  • Cestodes
  • Nematodes
  • Trematodes
  • Acanthocephalans
  • Cyamus nodosus whale lice
  • Cyamus monodontis whale lice
  • Porrocaecum decipiens nematode
  • Anisaki simplex nematode
  • Stenurus alatus nematode
  • Halocercus monoceris nematode

Economic Importance for Humans: Positive

Narwhals have traditionally been an important resource for the people of Greenland and Canada. Even though some of the carcass is wasted, Eskimos used to make use of most of the whale. The blubber and oil were used for lighting, heating and cooking. Narwhal skin, known as muktuk to natives, was an important part of their diet. It provided the vitamin C that they could not get otherwise. Sinews from the narwhals were traditionally used as thread. The meat of the narwhal can be consumed by humans Homo sapiens, but is more frequently used as dog food for the working dogs Canis lupus familiaris. The tusks were originally used as the tips of spears or harpoons, but later proved much more useful for trading. In the northern parts of Greenland many people still live a traditional Eskimo life, so the narwhal is still a very important resource for them. This way of life is also making a reappearance in Canada, where it is more economical to use working dogs than snowmobiles. Narwhals have also been caught by commercial whalers and kept because the tusk is so valuable. This hunting, however, was usually intended to catch bowhead whales, Balaena mysticus; the narwhals were just an accidental catch. (Jefferson, et al., 2013; Klinowska, 1991; Reeves and Tracey, 1980)

  • Positive Impacts
  • food
  • body parts are source of valuable material

Economic Importance for Humans: Negative

There are no known negative effects of narwhals on humans. (Reeves and Tracey, 1980)

Conservation Status

Narwhals are listed in CITES Appendix II; although not currently in danger of extinction, without control of trade they may become endangered. The IUCN Red List lists the narwhal listed as "near threatened." They have also previously been listed as data insufficient by the IUCN, because of the lack of certainty about their population size as a whole, and the evidence of population decline in some subpopulations.

There are concerns for the future of the narwhal population size due to hunting by humans. While some countries have limitations in place, others do not. Even with rules concerning how many narwhals can be taken, there is still the uncertainty of how many individuals are lost due to injuries incurred while being hunted. Apart from human hunting, narwhals are also vulnerable to population decline as a result of shipping patterns. The route taken by ships often cross the narwhal’s migration pattern, which results in the death of some narwhals. Climate change is also a third threat to narwhals, however, the first two threats are more likely to decrease their population size first and are therefore, a more immediate concern.

A ban on narwhal ivory has been established in the European Union in the hopes it will decrease the number of narwhals killed for their tooth. (Jefferson, et al., 2013; Klinowska, 1991)

Contributors

Ann Dunford (author), Radford University, Karen Powers (editor), Radford University, Tanya Dewey (editor), University of Michigan-Ann Arbor.

Glossary

Arctic Ocean

the body of water between Europe, Asia, and North America which occurs mostly north of the Arctic circle.

Atlantic Ocean

the body of water between Africa, Europe, the southern ocean (above 60 degrees south latitude), and the western hemisphere. It is the second largest ocean in the world after the Pacific Ocean.

World Map

Nearctic

living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.

World Map

Palearctic

living in the northern part of the Old World. In otherwords, Europe and Asia and northern Africa.

World Map

acoustic

uses sound to communicate

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

carnivore

an animal that mainly eats meat

chemical

uses smells or other chemicals to communicate

cryptic

having markings, coloration, shapes, or other features that cause an animal to be camouflaged in its natural environment; being difficult to see or otherwise detect.

echolocation

The process by which an animal locates itself with respect to other animals and objects by emitting sound waves and sensing the pattern of the reflected sound waves.

endothermic

animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.

female parental care

parental care is carried out by females

food

A substance that provides both nutrients and energy to a living thing.

holarctic

a distribution that more or less circles the Arctic, so occurring in both the Nearctic and Palearctic biogeographic regions.

World Map

Found in northern North America and northern Europe or Asia.

male parental care

parental care is carried out by males

migratory

makes seasonal movements between breeding and wintering grounds

molluscivore

eats mollusks, members of Phylum Mollusca

motile

having the capacity to move from one place to another.

natatorial

specialized for swimming

native range

the area in which the animal is naturally found, the region in which it is endemic.

pelagic

An aquatic biome consisting of the open ocean, far from land, does not include sea bottom (benthic zone).

piscivore

an animal that mainly eats fish

polar

the regions of the earth that surround the north and south poles, from the north pole to 60 degrees north and from the south pole to 60 degrees south.

saltwater or marine

mainly lives in oceans, seas, or other bodies of salt water.

seasonal breeding

breeding is confined to a particular season

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

sexual ornamentation

one of the sexes (usually males) has special physical structures used in courting the other sex or fighting the same sex. For example: antlers, elongated tails, special spurs.

social

associates with others of its species; forms social groups.

tactile

uses touch to communicate

ultrasound

uses sound above the range of human hearing for either navigation or communication or both

viviparous

reproduction in which fertilization and development take place within the female body and the developing embryo derives nourishment from the female.

References

Auger-Methe, M., M. Marcoux, H. Whitehead. 2011. Computer-assisted photo-identification of narwhals. Arctic, 64/3: 342-352.

Bobechko, L., S. Stockton. 2006. Mystery of the narwhal tusk. Alternatives Journal, 32/1: 4-5.

Dietz, R., M. Heide-Jorgensen, P. Richard, J. Orr, K. Laidre, H. Schmidt. 2008. Movements of narwhals (Monodon monoceros) from Admiralty Inlet monitored by satellite telemetry. Polar Biology, 31/11: 1295-1306.

Gjertz, I. 1991. The narwhal, Monodon monceros, in the Norwegian high Arctic. Marine Mammal Science, 7/4: 402-408.

Hayssen, V. 1993. Asdell's Patterns of Mammalian Reproduction: A Compendium of Species-Specific Data. Ithaca: Comstock Publishing Associates.

Heide-Jorgensen, M., E. Garde. 2011. Fetal growth of narwhals (Monodon monoceros). Mammal Marine Science, 27/3: 659-664.

Heide-Jorgensen, M., P. Richard, R. Dietz, K. Laidre. 2013. A metapopulation model for Canadian and west Greenland narwhals. Animal Conservation, 16/3: 331-343.

Heide-Jorgensen, M., R. Dietz, K. Laidre, P. Richard, J. Orr, H. Schmidt. 2003. The migratory behaviour of narwhals (Monodon monoceros). Canadian Journal of Zoology, 81/8: 1298-1305.

Jefferson, T., L. Karkzmarski, K. Laidre, G. O'Corry-Crowe, R. Reeves, L. Rojas-Brancho, E. Secchi, E. Slooten, B. Smith, J. Wang, K. Zhou. 2013. "IUCN Red List of Threatened Species" (On-line). Monodon monoceros. Accessed April 04, 2014 at http://www.iucnredlist.org/details/summary/13704/0.

Klinowska, M. 1991. Dolphins, Porpoises and Whales. The IUCN Red Data Book. Gland, Switzerland: IUCN.

Laidre, K., M. Heide-Jorgensen. 2005. Winter feeding intensity of narwhals (Monodon monoceros). Marine Mammal Science, 21/1: 45-57.

Laidre, K., M. Heide-Jorgensen, O. Jorgensen, M. Treble. 2004. Deep-ocean predation by a high Arctic cetacean. ICES Journal of Marine Science, 61/3: 430-440.

Lydersen, C., A. Martin, I. Gjertz, K. Kovacs. 2007. Satellite tracking and diving behaviour of sub-adult narwhals (Monodon monoceros) in Svalbard, Norway. Polar Biology, 30/4: 437-442.

Marcoux, M. 2008. Social behaviour, vocalization and conservation of narwhals. Arctic, 61/4: 456-460.

Marcoux, M., M. Auger-Methe, M. Humphries. 2012. Variability and context specificity of narwhal (Monodon monceros) whistles and pulsed calls. Marine Mammal Science, 28/4: 649-655.

Nielsen, M., H. Meilby. 2013. Quotas on narwhal (Monodon monceros) hunting in East Greenland: Trends in narwhal killed per hunter and potential impacts of regulations on Inuit communities. Human Ecology, 41/2: 187-203.

Nweeia, M., F. Eichmiller, P. Hauschka, E. Tyler, J. Mead, C. Potter, D. Angnatsiak, P. Richard, J. Orr, S. Black. 2012. Vestigial tooth anatomy and tusk nomenclature for Monodon monceros. The Anatomical Record, 295/6: 1006-1016.

Palsboll, P., M. Heide-Jorgensen, R. Dietz. 1997. Population structure and seasonal movements of narwhals, Monodon monoceros, determined from mtDNA analysis. Heredity, 78/3: 284.

Reeves, R., S. Tracey. 1980. Monodon monoceros. Mammalian Species, 127: 1-7.

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