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Monodon monoceros Linnaeus, 1758Narwhal |
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Monodon monoceros
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By Chad Drury
Narwhals ( Monodon monoceros ) are regularly found eastwards from the Canadian Arctic to central Russia, but occur infrequently or rarely in eastern Siberia, Alaska, and the western Canadian Arctic. They mostly remain above the Arctic Circle year-round, but stragglers have been recorded around Newfoundland, Europe, and the eastern Mediterranean (Minasian, 1984).
Biogeographic Regions:
arctic ocean
(
native
).
Monodon monoceros occupies one of the most northerly habitats of any cetacean species, between 70°N and 80°N, and seems to have more specific habitat requirements, and thus a more restricted range, than other cetaceans. Narwhals are rarely found far from loose pack ice and they prefer deep water. There are large concentrations in the Davis Strait, around Baffin Bay, and in the Greenland Sea. The advance and retreat of the ice initiates migration.
During summer, narwhals occupy deep bays and fjords; the best known and probably largest narwhal population in the world inhabits the deep inlets, sounds and channels of the eastern Canadian Arctic and north-west Greenland. When ice cover is low in larger, deeper water bodies, they move to smaller water bodies, which are steep-sided and deep. These traditional summering areas at the heads of fjords are probably important areas for calving. The narwhal’s preference for deep water in summer separates them from beluga whales which spend the summer mainly in shallow estuaries and bays (Klinowska, 1991).
These animals are found in the following types of habitat:
polar
.
Head and body length, exclusive of the tusk, is 360-620 cm, pectoral fin length is 30-40 cm, and expanse of the tail flukes is 100-120 cm. According to Reeves and Tracey (1980) average head and body length is about 470 cm in males and 400 cm in females and average weight is 1,600 kg in males and 900 kg in females. About one-third of the weight is blubber. Coloration becomes paler with age. Adults have brownish or dark grayish upper parts and whitish underparts, with a mottled pattern of spots throughout. The head is relatively small, the snout blunt, and the flipper is short and rounded. There is no dorsal fin, but there is an irregular ridge about 5 cm high and 60-90 cm long on the posterior half of the back. The posterior margins of the tail flukes are strongly convex, rather than concave or straight as in most cetaceans.
There are only two teeth, both in the upper jaw. In females the teeth usually are not functional and remain embedded in the bone. In males the right tooth remains embedded, but the left tooth erupts, protrudes through the upper lip, and grows forward in a counterclockwise spiral pattern to form a long, straight tusk. The tusk is about one-third to one-half as long as the head and body and sometimes reaches a length of 300 cm and a weight of 10 kg. In rare cases the right tooth also forms a tusk, but both tusks are always twisted in the same direction. Occasionally one or even two tusks develop in a female. The distal end of the tusk has a polished appearance, and the remainder is usually covered by a reddish or greenish growth of algae. There is an outer layer of cement, an inner layer of dentine, and a pulp cavity that is rich in blood. Broken tusks are common, but the damaged end is filled by new dentine growth (Reeves & Tracey, 1980).
Some key physical features:
endothermic
; homoiothermic;
bilateral symmetry
.
Sexual dimorphism:
male larger,
ornamentation
.
The mating system of narwhals is unknown.
Monodon monoceros is a seasonal breeder. The gestation period is about 15.3 months, with mating occurring in March-May and calving in July-August of the following year. Lactation duration is unknown, but thought to be comparable to the white whale ( Delphinapterus leucas ) of 20 months. The interval between successive conceptions is normally three years. Monodon monoceros copulate vertically in the water, belly to belly. Infant narwhals are usually implanted in the left uterine horn. A single calf is often the result of gestation, yet some twins have been recorded. Birth takes place tail first (Klinowska, 1991). The newborn is born with 25 mm of blubber. Calves usually measure between 1.5 and 1.7 m and weigh 80 kg. Physical maturity is attained at a length of 4 m and a weight of 900 kg in females and 4.7 m and 1600 kg in males. This usually corresponds to 4 to 7 years of age (Reeves & Tracey, 1980).
Key reproductive features:
iteroparous
;
seasonal breeding
; gonochoric/gonochoristic/dioecious (sexes separate);
sexual
;
fertilization
(
internal
);
viviparous
.
Young narwhals are capable of swimming soon after birth. They are nursed and protected by their mothers for extended periods after birth.
Parental investment:
precocial
; pre-fertilization (provisioning, protecting: female); pre-hatching/birth (provisioning: female, protecting: female); pre-weaning/fledging (provisioning: female, protecting: female); pre-independence (provisioning: female, protecting: female); extended period of juvenile learning.
Monodon monoceros may live up to 50+ years in the wild, yet attempts at captive breeding have been unsuccessful. Upon reaching the captive establishment, M. monoceros have only survived from 1 to 4 months. Considering the adult male can grow to 7m long, the species is usually too big to keep in captivity except at the largest of establishments (Klinowska, 1991).
Monodon monoceros is a gregarious species commonly found in pods of six to twenty individuals, though most groups tend to have three to eight individuals. These groups are often segregated by sex, with pods of male 'bachelors' being common. The smaller groups tend to gather together during migration seasons to form herds of hundreds or even thousands.
Monodon monoceros remains in the vicinity of pack ice throughout the year. Breathing holes are maintained through sheets of ice by thrusts of their thick melon, sometimes by several animals at once.
There are various hypotheses for the function of the tusk. Monodon monoceros may use it like male deer, for male-male competition. It also may be used to spear food. During deep dives, the tusk may be helpful in stirring up food from bottom sediments. Since most females are tuskless, the most likely hypothesis is that the tusk is a secondary sexual characteristic and may be the result of sexual selection by females (Reeves & Tracey, 1991).
Narwhals have a varied diet, feeding upon squid, fish and crustaceans. With few functional teeth this animal is thought to use suction and the emission of a jet of water to dislodge prey such as bottom-living fish and molluscs. Their highly flexible necks aid in scanning a broad area and the capture of more mobile prey.
Foods eaten include: Polar cod, Greenland halibut, flounder, salmon, herring, crustaceans and cephalopods (octopuses and squids).
Primary Diet:
carnivore
(
piscivore
, eats non-insect arthropods,
molluscivore
).
Animal Foods:
fish; mollusks; aquatic crustaceans.
Some have suggested that the tusk is used for anti-predatory functions, this is unsupported by evidence. Nonetheless, the tusk, which can grow to 3 m, would be a formidable weapon.
Narwhals harbour several species of commensal animals such as whale lice and certain nematodes. They act to limit the populations of their prey species.
There are no known adverse affects to humans.
Historically narwhals were a staple food source of many Arctic peoples. Arctic people used the narwhals body for a number of other uses. The blubber can be rendered for oil, the sinew used as thread, and the tusks traded and carved.
Ways that people benefit from these animals:
food
;
ecotourism
; research and education.
IUCN Red List:
[link]
:
Data Deficient.
US Federal List:
[link]
:
No special status.
CITES:
[link]
:
Appendix II.
Monodon monoceros is listed as CITES Appendix II and IUCN Data Deficient. As in most ivory bearing mammals around the world, destruction of individuals for their ivory is a constant threat. ( Klinowska, 1991 )
Narwhals are hunted from the ice, from boats and from kayaks in Canada and Greenland. The Inuit people prize them for their skin (known as mattak or muktuk), which is eaten in the traditional way - raw with a thin layer of fat. The tusk of the Narwhal is also prized, this time as a money-earner: tourists and collectors pay handsomely for the sea-unicorn's horn.
Estimated Current Population: 25,000-45,000 animals (Klinowska,1991).
Find Monodon monoceros information at
Chad Drury (author), University of Northern Iowa.
Jim Demastes (editor), University of Northern Iowa.
To cite this page: Drury, C. 2002. "Monodon monoceros" (On-line), Animal Diversity Web. Accessed February 09, 2010 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Monodon_monoceros.html.
Disclaimer: The Animal Diversity Web is an educational resource written largely by and for college students . ADW doesn't cover all species in the world, nor does it include all the latest scientific information about organisms we describe. Though we edit our accounts for accuracy, we cannot guarantee all information in those accounts. While ADW staff and contributors provide references to books and websites that we believe are reputable, we cannot necessarily endorse the contents of references beyond our control.
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