The narwhal, often called the “unicorn of the sea,” is instantly recognizable by the long, spiraled projection extending from its head. This unique appendage can reach lengths of up to 10 feet. For centuries, researchers speculated about its function, proposing uses from spearing prey to breaking ice. The central question remains: what is this structure actually used for by the elusive Arctic whale?
Anatomy of the Tusk: A Tooth, Not a Horn
The narwhal’s tusk is not a horn; it is an elongated canine tooth, typically the left one, that spirals counter-clockwise through the whale’s upper lip. This tooth is found primarily in males, though about 15% of females also grow one, usually shorter. Unlike other mammalian teeth, it lacks the hard outer enamel layer above the gum line.
The tusk is covered by a porous layer of cementum and dentin, which contains microscopic channels called dentinal tubules. These tiny tubes run from the surface all the way to the central pulp cavity, which is filled with nerve tissue. The entire tusk is highly flexible and contains an estimated 10 million nerve endings that connect directly to the narwhal’s brain.
Primary Role: A Unique Sensory Organ
The primary function of the tusk is now understood to be a specialized sensory organ that allows the narwhal to monitor its Arctic environment. The tusk’s porous, enamel-less surface enables seawater to enter the dentinal tubules. This direct connection between the ocean water and the nerve endings allows the whale to detect subtle changes in the chemistry and physics of its environment.
The tusk is sensitive to variations in water salinity, temperature, and pressure. Detecting salinity changes is important in the narwhal’s icy habitat, as salt concentrations increase when seawater begins to freeze. Sensing the salt concentration helps the narwhal predict the formation of new ice, allowing them to avoid becoming trapped beneath the ice sheet.
In one experiment, scientists observed a change in a narwhal’s heart rate when alternating solutions of high-salt and fresh water were applied to the tusk. This demonstrates that the tusk acts as a direct line of communication between the ocean and the whale’s nervous system. This sensory data also aids in foraging by helping the whale locate prey concentrations. Furthermore, the tusk has been observed being used to stun fish like Arctic char before consuming them.
Social Dynamics and Display
Beyond its sensory function, the tusk plays a significant role in the narwhal’s social structure and sexual selection. The presence of a long tusk in males suggests it is a secondary sexual characteristic, similar to the antlers of a deer. Males with larger tusks are believed to be more dominant and successful in attracting mates, as tusk size may signal overall health and fitness.
Narwhals engage in a distinctive behavior known as “tusking,” where two males gently cross and rub their tusks against each other. This ritualized action is thought to be a non-aggressive way for males to assess an opponent’s qualities or establish social hierarchy. Tusking may also serve the practical purpose of helping to clean the tusk’s sensitive surface, removing algae or other encrustations.
While the tusk has been observed being used to deliver forceful movements to stun prey, the idea that it is primarily a weapon for spearing fish or jousting opponents is now considered a secondary use. Evidence like head scarring and broken tusks indicates that some fighting occurs. However, the tusk’s sensitivity and flexibility point toward its main behavioral roles being focused on display, dominance signaling, and social interaction within the pod.