Superfish

Marine biologist-filmmaker Rick Rosenthal documents billfish (marlins, sailfish and swordfish), whose numbers have dwindled over the past 50 years from overfishing. Included: off Mexico's Contoy Island, he finds thousands of sailfish feasting on sardines; and along Australia's Great Barrier Reef, he swims with a "grander" (a marlin over 1000 pounds).