1 of 5 2 of 5

Last summer, Vancouver-based writer and photographer Isabelle Groc travelled to Baffin Island in Nunavut, to track narwhals, one of the most elusive species in the world. She joined a two-week narwhal research expedition, and reports on her Arctic journey and close encounters with the "sea unicorn".

This article is the sixth in a 10-part series. Read part five here.

Scientists define the narwhal as a toothed whale, but technically it has no teeth in its mouth. Instead the male (and rarely the female) develops a long spiral tooth that protrudes two to three meters out of the upper left jaw. This is the tusk, the most fascinating narwhal feature and the source of the unicorn myth.

Males usually have a single tusk though they sometimes have two tusks. Double-tusked narwhals are most commonly males although females can also have them. They are rare, and it is estimated that approximately 1.5 percent of narwhal are double tusked. Just before leaving for Tremblay Sound, we visited a hunter in Pond Inlet who had recently caught a double-tusked narwhal.

The narwhal tusk has always been a mystery. For years, persevering scientists have tried to understand the purpose of the tusk and have proposed several explanations: breaking ice, sword fighting, spearing fish for food, showing off to attract females.

None of these theories have been proven, and more than 10 years ago, a Connecticut-based dentist started investigating nature’s largest tooth.

Martin Nweeia, a professor at the Harvard School of Dental Medicine and a Smithsonian Institution researcher became passionately curious about the function of the tooth. “Why would an animal devote all its tooth growing potential to grow this huge thing? Why do that from an evolutionary standpoint? It had to be something compelling,” he told me while we were watching the net. “There are multiple aspects to the whale that defy evolution. Everything I learned in dental school, these guys break the rule.”

To solve this mystery, Nweeia turned to the Inuit elders and hunters who had lived close to the narwhal for thousands of years. Learning from their traditional knowledge that narwhal tusking was not a sign of aggression, Nweeia went on a different path and examined tusk specimens with a microscope.

He discovered that the narwhal tusk had millions of tiny nerves reaching from its surface to the central core and, ultimately, the whale's brain. Nweeia’s discovery was a turning point. It was the first time that anyone had ever considered the tusk as a sensory organ, capable of detecting changes in the ocean environment.

Nweeia joined our field research expedition to validate his theory and run more tests on live whales in the ocean environment. It was impressive to watch him carry out his experiments on the tusks of the two male narwhals we captured during the trip.

In order to measure the narwhal’s response to salinity, he exposed the tusk to different saltwater and freshwater solutions and used a Holter to monitor the whale’s heart activity. The changes in the heart rate allowed Nweeia to assess the whale’s sensitivity to saltwater. “We needed a variable that was visual, readable, understandable, and something that we could reproduce,” he explained.

Nweeia’s long-term passion for uncovering the secrets of this extraordinary tooth was obvious. He was running his experiments with the focused precision that one would expect from a dentist.

While the scientists were at work, I had a close look at the tusks of the two males we caught in the net. They looked strong but also surprisingly fragile. One of the tusks had a broken tip.

Meanwhile, James Simonee, the Inuit captain on our expedition, had an entirely different perspective on narwhal tusks. Before we left Pond Inlet for our expedition, he proudly showed us the tusk of a narwhal he had recently caught.

James Simonee displays a 2.5-metre tusk. Isabelle Groc

Simonee, who sells the tusks from the narwhals he hunts, had never caught an animal with such a long tusk before— 2.5 metres. “My father was jealous when I showed him the tusk I got,” he said.