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"Unicorn of the Sea"Successful hunters defin a narwhal in Qaanaaq, Greenland. In addition to its meat, indigenous peoples across the Arctic hunt the narwhal for its skin, which is an important source of vitamin C, and for its long tusk, which once earned the animal the moniker "unicorn of the sea."During Europe's Middle Ages narwhal tusks were worth ten times their weight in gold—and today they can still fetch hunters more than $1,000 apiece.(See National Geographic magazine's Hunting Narwhals.)Narwhal numbers across the Arctic aren't well known but the animals aren't believed to be at risk of extinction. Nonetheless the Convention on International Trade in Endangered Species (CITES) warns that future extinction could be possible if the trade in valuable narwhal ivory isn't closely monitored and controlled. Already, some regional populations are in serious trouble, including those along Greenland's west coast, where narwhals are disappearing under catch limits that many marine scientists insist are far too high.—Brian Handwerk

Photograph by Staffan Widstrand, Corbis