Description
These are medium-sized whales, being around the same size as a beluga whale. Total length in both sexes, excluding the "tusk" of the male, can range from 3.95 to 5.5 m (12 ft 12 in to 18 ft 1 in). Males, at an average length of 4.1 m (13 ft 5 in), are slightly larger than females, at an average of 3.5 m (11 ft 6 in). Typical adult body weight can range from 800 to 1,600 kg (1,800 to 3,500 lb). Males attain sexual maturity at 11 to 13 years of age, when they are approximately 3.9 m (12 ft 10 in) long, and females attain maturity at 5 to 8 years old, when they are 3.4 m (11 ft 2 in) long. The pigmentation of the narwhal is a mottled pattern, with blackish-brown markings over a white background. They are darkest when born and become whiter in color with age, with white patches developing on the navel and genital slit at sexual maturity. Old males may be almost pure white.
The most conspicuous characteristic of the male narwhal is its single extremely long tusk, a canine tooth that projects from the left side of the upper jaw and forms a left-handed helix. The tusk seems to grow slightly throughout life from 1.5 to 3.1 m (4 ft 11 in to 10 ft 2 in). Despite its formidable appearance, the tusk is hollow and weighs only around 10 kg (22 lb). About one in 500 males has two tusks, which occurs when the right canine, normally small and less straight, also grows out. A female narwhal has a shorter, and straighter tusk. She may also produce a second tusk, but this occurs rarely, and there is a single recorded case of a female with dual tusks.
The most broadly accepted theory for the role of the tusk is as a secondary sexual characteristic, similar to the mane of a lion or the tail feathers of a peacock. This hypothesis was notably discussed and defended at length by Charles Darwin, in The Descent of Man, and Selection in Relation to Sex (1871). It may help determine social rank, maintain dominance hierarchies, or help young males develop skills necessary for performance in adult sexual roles. Narwhals have rarely been observed using their tusk for fighting, other aggressive behavior or for breaking sea ice in their Arctic habitat. Some narwhals have a second, small tooth in their mouths, but are essentially toothless.The tusk may be a sensory organ.
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