The largest-ever study of whale shark migrations, nine years in the making, shows that the hundreds of school bus-sized animals that feed in a plankton-saturated stretch off the Mexican coast come from far and wide.

The gentle giants—which can reach up to 40 feet (12 meters) or longer in length, and weigh an average of 5 tons—use mouth filters to feed on the tiny plankton and small fish or eggs.

Whale sharks are known to gather at a dozen major feeding locations around the world, from western Australia and Indonesia to Belize. But between May and September, the waters of Mexico's Quintana Roo state, on the northeastern Yucatan Peninsula, draw far more animals than other spots and attract an estimated 800