97 MILES OFFSHORE FLORIDA — The scientist outstretches his arm as he rushes toward the largest fish in the sea. He keeps a white-knuckle grip on his camera, his dive fins thrashing, propelled by what he knows is a razor-thin window to pull off this scientific mission: Swim to, then keep pace with, the feeding whale shark just long enough to document the unique patterns on its body. But the shark is moving quickly — up to 3 mph, fast for a human fighting waves and currents.