Narwhals are medium-sized Arctic whales, 4-5.5 meters (13-18 feet) long and weighing 800-1,600 kg (1,800-3,500 lbs). Calves are born grey-brown, adults become mottled grey and white, and the oldest animals turn almost completely white.
Their most famous feature is the tusk, which is actually a tooth. The left upper canine grows straight through the lip in a counter-clockwise spiral and can reach 3 meters (10 feet). Nearly all males have one, a few females do, and very rarely a narwhal grows two. The tusk is packed with nerve endings and is thought to sense changes in the water, as well as to signal status among males.
Narwhals have no dorsal fin, which helps them swim beneath sea ice, and a thick layer of blubber that can make up a third of their weight. They live around 50 years.
Narwhals live further north than almost any other whale, in the Arctic waters of Canada, Greenland, Svalbard and Russia. In summer they gather in shallow coastal bays and fjords. In winter they move offshore into Baffin Bay and the Davis Strait, where they live under dense pack ice, surfacing to breathe through cracks and small openings.
They are among the deepest-diving mammals, regularly reaching 800 meters (2,600 feet) and sometimes more than 1,500 meters (5,000 feet).
Narwhals eat Greenland halibut, Arctic cod and polar cod, along with squid and shrimp. They have no functional teeth in their mouth, so they suck prey in whole.
Most of their feeding happens during the dark winter months on the deep seabed, and far less during the summer. Researchers have filmed narwhals using the tusk to stun fish with a quick tap before eating them.
Narwhals travel in groups of 10-20, and in summer these groups join into gatherings of hundreds or even thousands. They are slow, careful swimmers and are easily startled, which makes them hard to study.
Males sometimes rub their tusks together at the surface, a behaviour called tusking that is probably a way of sorting out rank. Like other toothed whales they use clicks to echolocate and whistles and knocks to communicate.
The narwhal, Monodon monoceros, shares the family Monodontidae with just one other species, the beluga. Its name means "one tooth, one horn". In medieval Europe narwhal tusks were sold as unicorn horns and were worth many times their weight in gold.
The IUCN lists the narwhal as Least Concern, with a population of roughly 170,000. Even so, narwhals are considered one of the Arctic mammals most at risk from climate change, because they depend on sea ice, follow fixed migration routes and are very sensitive to noise. Expanding shipping, oil and gas exploration, and orcas moving north into ice-free waters are all growing pressures. Inuit communities in Canada and Greenland hunt a regulated number each year.
