Mammals
Narwhal
Monodon monoceros · also called narwhale, unicorn of the sea
The narwhal is the unicorn of the sea — a medium-sized Arctic whale whose males carry a single long, straight, spiralled tusk. It lives farther north, dives deeper, and depends more completely on sea ice than almost any other whale, and it spends the darkest months of the year under the frozen ocean.
Overview
Narwhals live year-round in the high Arctic, in the fjords and offshore waters of Canada, Greenland, Svalbard, and the Russian Arctic. They are highly migratory within that range, spending summer in coastal bays and inlets and moving out in autumn to deep offshore areas along the pack-ice edge, where they overwinter in small openings (“leads”) in nearly complete ice cover. They are social, travelling in groups of a few to several dozen that gather into aggregations of hundreds or thousands on migration.
The tusk
The narwhal has only two teeth, both in the upper jaw, and in males the left one erupts through the lip and grows into a tusk — straight, tapering, up to about three metres long, and always spiralling anticlockwise. It is one of the few straight tusks in nature and the inspiration for the medieval “unicorn horn,” which was sold across Europe at enormous prices.
Its purpose is debated but increasingly understood as both a sexual signal and a sensory organ. Larger-tusked males have more mating success and spar with their tusks; at the same time the tusk is highly innervated and porous, and narwhals seem to read information about their environment — and to stun fish — with it.
A deep-diving specialist
In winter darkness, narwhals feed mainly on Greenland halibut and Arctic cod near the bottom of deep basins, making some of the deepest and longest dives of any marine mammal. They have no functional teeth for chewing, so prey is caught by suction and swallowed whole.
Reproduction
Narwhals mate in spring and, after a gestation of around 14 months, females give birth to a single grey calf in summer. Calves nurse for over a year and stay with the mother longer still. Females may not breed until 8 or 9 years old, and calving intervals are about three years, so the population grows slowly.
Threats and conservation
The narwhal is listed as Least Concern, but it is widely regarded as one of the Arctic species most exposed to climate change. Its reliance on predictable sea ice, its narrow diet, and its limited behavioural flexibility make it vulnerable as the ice retreats: killer whales are moving into newly open water and preying on narwhals, shipping and resource extraction bring noise and disturbance to once-inaccessible areas, and shifting ice raises the risk of mass entrapments, where groups become trapped by rapidly forming ice and drown or starve. Subsistence hunting by Inuit communities is managed under quotas in Canada and Greenland.
Narwhal: common questions
What is the narwhal's tusk actually for?
It is an enlarged tooth — almost always the left upper canine — that grows straight through the lip in a left-handed spiral. Its main function appears to be display and male-male competition — bigger-tusked males father more calves, and males "tusk" each other and cross tusks at the surface. But the tusk is also a genuine sensory organ, with around 10 million nerve endings connecting its core to the outside, and narwhals can apparently sense water salinity, temperature, and possibly prey through it. Occasionally females grow one, and rarely a male grows two.
Do narwhals use their tusk to hunt?
Not to spear prey, but drone footage from the Canadian Arctic has shown narwhals using the tusk to tap, stun, and manipulate fish before eating them, and possibly to flush prey from the seabed. It is not their primary hunting tool — they catch most food by diving deep and sucking fish into a toothless mouth — but it is not purely ornamental either.
How deep can a narwhal dive?
Among the deepest of any marine mammal. In winter, narwhals in Baffin Bay make repeated dives past 1,500 metres — sometimes to nearly 1,800 — to feed on Greenland halibut near the seafloor, staying down for around 25 minutes. Their bodies are adapted for it, with a compressible ribcage, high concentrations of oxygen-binding myoglobin in the muscle, and the ability to shut down blood flow to non-essential organs.
Are narwhals endangered?
They are currently listed as Least Concern, with a global population of roughly 120,000. However, narwhals are considered one of the Arctic marine mammals most vulnerable to climate change. They are extreme specialists — tied to specific ice-edge habitats and a narrow diet, and slow to adapt behaviourally — and the loss of sea ice exposes them to killer whale predation, shipping noise, and industrial activity in waters that used to be sealed off by ice for much of the year.