Massive shark turnout near Yucatan sets record

So much for the previous assumption that whale sharks were solitary denizens of the deep. As many as 420 - count `em - 420 whale sharks crowded into a 7 square mile patch of ocean off the coast of Mexico's Yucatán Peninsula in 2009 - the largest such sighting ever recorded.

Not a lot is known about whale sharks, which can reach 40 feet in length and weigh more than 79,000 pounds. But a new report, citing this spectacular gathering - as well as other evidence compiled by researchers - suggests that the creatures actually "are gregarious and form seasonal aggregations in some coastal waters."

So what brought so many whale sharks to this one locale - a gathering, known as an "afuera" (Spanish for "outside") - at a single time? In a word, food.

"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," said Mike Maslanka, biologist at the Smithsonian Conservation Biology Institute and head of the Department of Nutrition Sciences. "Our research revealed that in this case, the hundreds of whale sharks had gathered to feed on dense patches of fish eggs."

Marine biologists began to take an interest in the area following anecdotal reports provided by local fishermen as far back as 1991 of large whale shark gatherings. That led to 34 aerial surveys over the Afuera between 2005 and 2009. The scientists' findings are published in the April edition of the scientific journal PLoS ONE.