To celebrate World Oceans Day, we"re swimming through a shoal of jack fish just off the coast of Baja, California, in Cabo Pulmo National Park. This Mexican marine park in the Sea of Cortez is home to the northernmost and oldest coral reef on the west coast of North America, estimated to be about 20,000 years old. Jacks are clearly plentiful here, but divers and snorkelers in Cabo Pulmo can also come across many other species of fish and marine mammals, including several varieties of sharks, whales, dolphins, tortoises, and manta rays.