The unicorn of the sea
Narwhals are whales. They live year round in the cold waters in the Arctic Circle.
Like all whales, they are mammals. This means they are warm-blooded and give birth to live babies.
Males can be 5 metres long and weigh up to 1,600kg. Females are usually 3.5 metres long and weigh around 1,000kg.
They feed on fish, squid and shrimp, beneath the Arctic pack ice. They are hunted by killer whales, polar bears and people.
What makes narwhals unusual is that the males have a long tusk. It is a long ivory tooth between 2 and 3 metres long.
This tooth sticks out like a horn, making the animals look like unicorns.
Narwhals have lungs and breathe air just like you do. However, they can hold their breath much longer than we can.
When hunting for fish, the mammals can dive to 1,500 metres below the surface of the sea. They can stay underwater for 25 minutes at a time. They sometimes make more than 15 dives a day.
By the numbers
Scientists think there are about 75,000 narwhals in the world.
The Inuit people in Greenland and Canada kill more than 1,000 every year. They give the meat to their dogs, and make money by selling the tusks. Many tusks are used in traditional Chinese medicine.
Climate change and pollution are also taking their toll on narwhals.
Another problem is that the animals are slow breeders. Females give birth for the first time when they are six or seven years old. Their calves live with them for the first year.
The narwhal is not officially endangered. However, scientists say too many are being killed. If you want to help the narwhal, don't buy traditional medicines made from their horn.
In medieval times, narwhal tusks were sold as unicorn horns. They were very expensive but people bought them just the same because they thought they had magical powers.
The tusks were believed to cure many illnesses. People also thought that the tusks could make poison harmless so some kings and queens even had drinking cups made from them.
One narwhal horn cup that belonged to Queen Elizabeth I of England cost GBP10,000 - the same price as a castle at the time.
How the narwhal got its horn
The Inuit people who live in the Arctic Circle have a legend that explains how the narwhal got its tusk.
Once upon a time, they say, a woman went fishing. She used a long harpoon, a kind of spear.
Yet she was careless and fell into the sea. As she splashed about, a beluga whale came up to see what was happening.
When the whale got close, the woman speared it with her harpoon. The spear stuck in the whale's nose.
That is how the first narwhal got its horn.
The tusk that baffles scientists
All male narwhals have long tusks. Some females have tusks, but most don't. Some have two tusks. The tusk is an overgrown tooth.
Scientists don't really know why the narwhal grew a tusk. Some think it is just for show. Long ago, scientists thought the tusk was used to spear fish. Others think it's used to fight.
But they have discovered that the tusk is very sensitive. The whales don't use their tusks for fighting. When they do touch tusks it is very gently.
The whale's tusk is the only straight tusk in the world. Elephant and other tusks usually grow curved.
Male narwhals are called bulls. Females are cows. Babies are calves.
A group is called a gam, pod, herd, or school.
Narwhals belong to the toothed whale family. The other branch of whales do not have teeth. They have baleen plates which are like giant hair brushes. They squeeze sea water through the hairs and catch tiny sea animals called plankton to eat.
Narwhals love to communicate. They make lots of sounds, including squeals, trills, whistles, and clicks.
Scientists are recording these sounds and hope to learn soon what each signal means.