Hammerheads school in enormous numbers. Coral reefs ripple with color by day but at night turn into killing grounds for packs of whitetip sharks. Pristine waters brim with tuna and dolphins in hot pursuit of clouds of fish. Isla del Coco, or Cocos Island, appears as a tiny dot on a map in the Pacific Ocean more than 300 miles off the coast of Costa Rica, and is home to one of the greatest concentrations of predators on the planet. Dive
