WASHINGTON, May 25 (UPI) -- Whale sharks, long thought to be solitary animals feeding in the open sea, have been recorded in huge groups feeding in coastal waters, U.S. researchers say.

While aggregations, or schools, of whale sharks ranging from several individual sharks to a few dozen have been seen in the past, new research by scientists at the Smithsonian Institution -- using both surface and aerial surveys -- has revealed an enormous aggregation of whale sharks, the largest ever reported, with as many as 420 individuals off the coast of the Yucatan Peninsula in Mexico.


Food is bringing them together in such large groups, a Smithsonian release said Wednesday.

"Whale sharks are the largest species of fish in the world, yet they mostly feed on the smallest organisms in the ocean, such as zooplankton," Smithsonian biologist Mike Maslanka said. "Our research revealed that in this case, the hundreds of whale sharks had gathered to feed on dense patches of fish eggs."

The research team also examined a nearby, less dense aggregation of whale sharks off the northern tip of the Yucatan Peninsula.

"With two significant whale shark aggregation areas ... the northeastern Yucatan marine region is a critical habitat that deserves more concerted conservation effort," Maslanka said.

Whale sharks, the heaviest and longest of all fishes at more than 40 feet long, are listed as "vulnerable" with the International Union for Conservation of Nature and Natural Resources.