This photo of a freshly cut dorsal fin from a scalloped hammerhead shark (Sphyrna lewini), was taken in 2006 on a long-lined fishing boat in Cocos Island, 300 miles off the Pacific coast of Costa Rica. Cocos was declared a UNESCO World Heritage site and is the home to one of the world's richest shark populations. It has also become a major target for long-lined shark fishing.

Every year, humans kill an estimated 100 million sharks. The threats we pose are many. By-catch: the accidental killing of sharks in fishing gear intended for other species. Illegal poaching and hunting: selling shark fins for soup and sportfishing for shark-jaw trophies. Nets: placed along coastlines to keep sharks away from beaches.  Removing sharks in large numbers can have ripple effects that throw entire ecosystems out of balance.

Discover more about shark biology, habitat, and status in the Great White Shark section, and check out the Smithsonian Ocean Portal's Top 5 Reasons you should Revere, Not Fear, the Shark.