After half a century of searching, scientists have finally discovered what happens to the world’s second largest shark every winter: It has a Caribbean hideout.

Basking sharks, which can grow up to 33 feet long and weigh more than a Hummer H1, spend the late spring, summer and early fall in the temperate regions of the world’s oceans. But then they pull their great disappearing act, eluding scientists throughout the winter months.

“It’s been a big mystery for the past fifty years,” said Greg Skomal, an aquatic biologist at the Massachusetts Division of Marine Fisheries and lead author of the study in Current Biology May 7. “For a while people thought they were hibernating on the sea floor, even though hibernating is not really something sharks do.”