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.

The basking shark is a benign behemoth. It swims at about three miles per hour with its four-foot-wide mouth gaping open, filtering through almost 500,000 gallons of water every hour for its plankton sustenance.

He found the sharks were traveling well-outside their known range, spending months in the warm waters of the Caribbean and even deep into the southern hemisphere. They also periodically dove to more than 3,000 feet, and often stayed at those depths for months at a time. One shark remained at a depth of nearly 600 feet for upward of five months.

“No one has ever seen a baby basking shark, no one’s found a pregnant shark, knows when they reproduce or what their gestation period is,” said Skomal.