Narwhals Use Their Tusk to Hunt. It Took 500 Years to Prove It.

For five centuries, the narwhal tusk was one of the most valuable objects in Europe. Sold as unicorn horn, it was believed to neutralize poison, cure disease, and detect the presence of evil. Queen Elizabeth I paid the equivalent of a castle for one. The tusk’s actual function, on the living animal in the Arctic Ocean, was a question that scientists debated for nearly as long without reaching consensus.

The leading hypotheses over the centuries included: a weapon for fighting, an ice-breaking tool, a sensory organ, a sexual display structure, and a hydrodynamic stabilizer. Most of these were proposed without direct observation of narwhals using their tusks for anything in particular, because narwhals are among the most difficult large mammals to study. They live in remote Arctic waters, spend significant time under sea ice, and are extraordinarily sensitive to disturbance.

The answer came in 2017 from drone footage captured by researcher Marianne Marcoux at Fisheries and Oceans Canada and colleagues, working with the World Wildlife Fund Canada. The footage showed narwhals using their tusks to stun Arctic cod with sharp, precise taps, immobilizing the fish before consuming them. The tusk is a hunting tool. Five hundred years of speculation, resolved by a drone.

The Tusk Itself

The narwhal tusk is a modified canine tooth that grows through the upper left lip of males, reaching lengths of up to 3 meters. It is the only straight tusk in nature, and it grows in a left-handed helix, spiraling counterclockwise when viewed from the tip. Females occasionally grow tusks, and rare individuals of both sexes grow two, but the single left tusk of the male is the defining feature of Monodon monoceros.

The tusk’s surface is covered in millions of microscopic tubules that connect to the nerve-rich pulp at the center, making it a highly sensitive sensory organ. Researcher Martin Nweeia at Harvard University has studied narwhal tusk sensory biology extensively, demonstrating that the tusk can detect changes in water temperature, salinity, and pressure. Narwhals have been observed flexing their tusks slightly in response to environmental stimuli, suggesting active sensory use.

The combination of hunting tool and sensory organ in a single structure is unusual in the animal kingdom, and it raises questions about how narwhals integrate the information from tusk sensation with their echolocation system, which they use for navigation and prey detection in the same way as other toothed whales.

Life Under the Ice

Narwhals spend more time under sea ice than any other cetacean. In winter, they move into areas of dense pack ice where leads, narrow channels of open water, provide breathing access. They navigate under ice for distances of up to 1.5 kilometers between breathing opportunities, using echolocation to find leads in complete darkness.

Researcher Kristin Laidre at the University of Washington has used satellite tags to track narwhal movements through the Canadian Arctic and Greenland, producing detailed data on how narwhals use sea ice habitat across seasons. Her work has shown that narwhals are highly faithful to specific wintering areas, returning to the same regions year after year, and that their distribution is tightly linked to sea ice conditions.

This fidelity to specific ice habitats makes narwhals particularly vulnerable to the rapid changes occurring in Arctic sea ice. Unlike some Arctic species that can shift their range as conditions change, narwhals show limited flexibility in their habitat use. Laidre’s modeling work suggests that narwhal habitat will be significantly altered by mid-century under current warming trajectories, with some traditional wintering areas becoming ice-free and therefore unsuitable.

The Population and the Hunt

The global narwhal population is estimated at approximately 170,000 individuals, concentrated in the Canadian Arctic and around Greenland. The species is listed as Least Concern on the IUCN Red List overall, though some subpopulations are considered more vulnerable.

Narwhals have been hunted by Inuit communities for thousands of years, providing meat, mattak (skin and blubber), and tusk ivory that has been central to Arctic cultures. The hunt is managed under quotas in Canada and Greenland, though the adequacy of those quotas relative to population dynamics is debated among researchers.

The tusk that was sold as unicorn horn across medieval Europe, that funded castles and decorated royal courts, that was the subject of five centuries of speculation about its function, is a hunting tool and a sensory organ used by an animal navigating under Arctic ice in complete darkness. Elizabeth I’s unicorn horn was a narwhal’s tooth. The narwhal itself is stranger than the unicorn ever was.