Tuesday, 28 December 2010

Narwhal: Unicorns of the Sea

Image showing four narwhals tusking
Male Narwhals
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Cetacea
Family: Monodontidae
Genus: Monodon
Species: Monodon monoceros
Conservation Status: Near Threatened
Common Name(s): Narwhal

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The Narwhal, or the unicorn of the sea as it is sometimes called, is a medium-sized toothed whale and one of the two surviving representatives of the Monodontidae family. The other member is the beluga whale (Delphinapterus leucas).

As you can see on the article's images and videos, these magnificent creatures are best known for the long straight tusks that male individuals feature. Let's learn more about these magnificent creatures.

Distribution
Narwhals occur predominantly in the Atlantic and Russian areas of the Arctic Ocean. They are commonly sighted 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). Lands falling under this strip include Svalbard, Franz Joseph Land, and Severnaya Zemlya. The northernmost recordings of narwhals come from the north of Franz Joseph Land, at about 85° North latitude. Most individuals are concentrated in the fjords and inlets of Northern Canada and western Greenland.

Narwhals can reach depths of 1,500 m (~4921 ft).

Map showing the distribution of Narwhals
Frequent (solid blue) and rare (striped blue) sightings of narwhals


Description
Narwhals are medium-sized whales, with their body length ranging from 3.3 to 5.5 m (~13 to 18 ft). Generally, males are slightly larger and heavier than females. Males have an average length of 4.1 m (~13.5 ft 5) and females an average length of 3.5 m (~11.4829 ft). Males have an average weight of 1,600 kg (~3,527 pounds) whereas females have an average weight of 1,000 kg (~2.204 lb).

Adults have a bluish-gray cylindrical body with white blotches. Newborns are darkest when born, becoming whiter and whiter as time passes and become whiter with age.  Old males are almost entirely white.

The species has no dorsal fin, most probably an evolutionary adaptation that allows them to swim under the ice with greater ease. In narwhals, the neck vertebrae are jointed,  instead of being fused like most whales. These traits are shared by the closely related beluga whale. The tail flukes of females have front edges that are swept back, and those of males have front edges that are more concave and lack a sweep-back. This adaptation is assumed to reduce drag caused by the tusks.

The head is round, featuring a small mouth and a blunt snout. The narwhal’s compact body shape, along with their thick layer of blubber (fat) helps them to retain heat in the icy Arctic waters they inhabit.

Males reach sexual maturity at 11 to 13 years of age, when they are about 3.9 m (~13 ft) long whereas females attain sexual maturity when they are 5 to 8 years old, at a length of about 3.4 m (~11 ft). Narwhals have a maximum lifespan of 50 years.

Photo of male narwhal captured and satellite tagged.

Tusks and Their Purpose
The long, hollow tusks that males feature are the most unique and distinctive trait of these strange animals. Each tusk is essentially an enlarge, canine tooth that protrudes from the left side of the upper jaw, through the lip, forming a left-handed helix spiral. They grow throughout life, commonly reaching lengths ranging from 1.5 to 3.1 m (~5 -10 ft).

The right incisor typically stays small. Interestingly, in about one in every 500 males the right canine grows as well, and the male gets to have two tusks! In rare occasions, females also have a tusk, which however is shorter and less-spiraled. It's possible for females two have two tusks as well, although there has been only one recorded dual-tusked female as of today.

The exact purpose(s) of the tusks has yet to be unveiled, although there are some good theories on the table. In most animals horns, tusks and other similar structures are a secondary sexual characteristic used by males to attract females (like a sign of manliness) and to assert dominance among other male competitors. Asserting dominance is probably excluded, since males rarely use them for fighting or other aggressive behaviors. However, they may help determine social rank, maintain dominance hierarchies, or help young males develop skills necessary for performance in adult sexual roles.

In the past, it was hypothesized that tusks are used for breaking the ice. But similarly to fighting, this occurs very rarely.

Recent research has shown that the tusk is an innervated sensory organ with millions of patent nerve endings connecting the external ocean waters with the brain. We still don't know what kind of information narwhals get through their tusks. One assumption is that they can sense changes in water temperature, pressure, and
salinity gradients.


Great Narwhal-footage by National Geographic



Diving
Narwhals are capable of really deep dives, among the deepest compared to other marine mammals, like mammals and dolphins. They routinely go 800 meters (~2,625 ft) deep, 15 or more times per day. Occasionaly, they will go even deeper,  reaching recorded depths of at least 1,500 meters (~4,921 feet). These deep dives last for about 25 minutes, including the time spent at the bottom and the transit down and back from the surface.


Diet
These specialized Arctic predators have a relatively restricted diet, primarily based on Greenland halibut (Reinhardtius hippoglossoides), Arctic cod (Boreogadus saida), cuttlefish, shrimps and armhook squid. Additional items researchers have found in their stomachs include:
  • Wolffish
  • Capelin
  • Skate eggs

Rocks have also been observed, probably accidentally ingested by feeding near the bottom.


Skull of a rare double-tusked narwhal

Predators
Humans excluded, narwhals have very few natural enemies, with predation accounting for a relatively small number of deaths. Polar bears sometimes swipe young narwhals at breathing holes whereas orcas can group together to hunt and kill a single narwhal. Additionally, Greenland sharks and walruses prey occasionally on juveniles and wounded or ill adults.

When it comes to escaping aquatic predators like killer-whales, they prefer to use their prolonged submergence to hide under the ice rather than relying on speed

Behavior
Narwhals usually stay in groups of five to ten individuals. During the summer, many groups come together and form even larger aggregations, ranging from 500 to over 1000 narwhals. Male narwhals are known to rub their tusks every now and then. This activity is called tusking and possibly functions as a means of maintaining social dominance hierarchies.

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, usually 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 leads.[24] As spring comes, these leads open up into channels and the narwhals return to the coastal bays.[25] 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.[23] Feeding in the winter accounts for a much larger portion of narwhal energy intake than in the summer.[23][24]

Reproduction
Very little is known about the reproductive patterns of the species. reproduction. This is because it is done in remote and hard to reach by humans areas. Mating occurs from March to May with the gestation period lasting for 10-16 months with new born calves being brown with no spots. They are 1.5 meter (5 feet) long and weigh 80 kg (175 pounds). They are weaned after 4 months after birth.

Females start bearing calves when six to eight years old. Adult narwhals mate in April or May when they are in the offshore pack ice. Gestation lasts for 14 months and calves are born between June and August the following year. As with most marine mammals, only a single young is born. Newborn calves average 1.6 metres (5.2 feet) in length and are dark grey. The 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. This long lactation period gives calves time to learn the skills they need for survival. Mothers and calves stay close and when travelling, the calf stays by its mother's back for assistance in swimming.

Conservation status and threats
Currently narwhals are listed by the IUCN as not threatened, with their total population estimated to be about 75,000 individuals. They have been traditionally hunted by Inuit people for more than a thousand years and this activity doesn't seem to threaten them. However they are believed to be particularly vulnerable to climate changes due to their narrow geographical range.

In captivity
As of now, no narwhals are kept in captivity as they tend to die very quickly from unknown reasons.

Narwhal and the myth of unicorns
According to many the myth of unicorns may originate from this species. During medieval times many Europeans believed that narwhal tusks are actually unicorn horns. It wasn't until the Age of Exploration that their true origin begun to unfold as explorers and naturalists began to visit Arctic regions.

Other Interesting Facts About Narwhals
- The word narwhal (pronounced NAR-wall or NAR-way-l) is said to derive from old Norse for "corpse whale," apparently because the animal's mottled, splotchy coloring recalled the grayish, blotched color of drowned sailors.
- Mortality often occurs when the narwhals suffocate after they fail to leave before the surface of the Arctic waters freeze over in the late autumn. Open water is formed in ice-covered water by fracturing events induced by strong winds, but when these conditions are absent ice can quickly form. The last major entrapment events occurred when there was little to no wind. The events can trap groups as large as 600 individuals. Most entrapment events occur in narwhal wintering areas such as Disko Bay. In the largest entrapment in 1915 in West Greenland, over 1,000 narwhals were trapped under the ice.

References

6 comments:

  1. best animal in the world

    ReplyDelete
  2. I used to think they were mythical creatures and that they didn't exist. people should be more aware of there awesomeness

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  3. narwhals are so legitiment i love them so much

    narwhals narwhals swimmin in the ocean causin a cmotion cuz they are so awesome narwhal narwhals swimmin in the ocean pretty big and pretty white theyd beat a polar bear in a fight

    animal taken by Kristin F

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  4. These animals are like unicorns that live in the ocean but are like whales

    ReplyDelete
  5. Magical unicor of the sea!

    ReplyDelete