Narwhals: Photos Show Decline of "Unicorn" Whales

Digital snapshots from above the Arctic have helped a researcher spot declining narwhal populations. The narwhal—a small Arctic whale known for its six-foot-long (1.8-meter-long) tusk—has dropped in numbers by an average of 6 percent per year during the last 17 years.

The narwhal's tusk, a spiraling extension from a male narwhal's lip and upper jaw, is actually an overgrown tooth. While the tusk's primary use may be to attract or impress females, researchers have also witnessed males jousting with their tusks. There are also theories that the tusk may be used by narwhals as a way to sense sound or electromagnetic waves.

The narwhal has often been associated with another one-horned creature, the unicorn. In medieval times traders would pass narwhal tusks off as unicorn horns, thought to have magical disease-curing powers. Queen Elizabeth I reportedly paid 10,000 pounds for a single narwhal tusk in the 16th century—that's about what it would have reportedly cost to build an entire castle at the time.