Never-seen-before footage of the narwhal has revealed an aspect of their physiology which has caused much debate: the ‘horn’ protruding from their heads.

Scientists have long speculated about the reason for its existence – from use as an ice pick or weapon to sexual selection and even echolocation.

One theory of how these whales use their tusks has finally been confirmed.

Footage captured by two drones in Tremblay Sound, Nunavat, in north-east Canada found the tusks are used to stun Arctic cod by ramming into them.

This behaviour briefly immobilises the fish, making them easy prey. The video was released by WWF Canada.

Brandon Laforest, a senior specialist of Arctic species and ecosystems, told National Geographic part of the mystery of narwhals is that they are notoriously shy creatures.

He said: “They don't jump like other whales. They are also notoriously skittish."

The tusk is a canine tooth which can grow to nine feet long from the head of adult males. It contains thousands of nerve endings which allows the narwhal to sense even the slightest movement around them.

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Narwhals are one of the few creatures whose food web is dependent on sea ice, making them especially susceptible to the detrimental effects of global warming.

In addition, an increase in tourism in the region means they are in danger of being struck by ships.