IMAGE shows a swimmer with a basking shark—a harmless plankton feeder—off the Cornish coast.

The basking shark (Cetorhinus maximus) is the second largest fish in the world, while the equally harmless whale shark (Rhincodon typus) is ranked as the world’s largest fish. These large sharks are slow-moving filter feeders, and both species are threatened by overfishing, since “they have a lengthy maturation time, slow growth rate and a long gestation period.”

Basking sharks can “attain lengths of at least 10 meters, but the average size is 7-9 meters and may live up to 50 years, [and] it is a highly migratory species.” Until now, data regarding the seasonal movements of basking sharks were incomplete. From the Washington Post:

Basking sharks were easy to spot in summer and fall. Many cruised near the surface off New England, filtering water through an impossibly wide mouth.

But then, in winter, the sharks vanished from these waters, and scientists couldn’t find them anywhere else. One guess was that they sank to the bottom and hibernated, waiting out a food shortage. But nobody knew for sure: The basking shark became a reminder of the unsolved mysteries of the oceans.

Last week, however, a group of researchers from Massachusetts and Maine said they had found the answer.

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Soon, the tags began popping up in places that nobody expected a basking shark to be: near the Bahamas, off Puerto Rico, even the mouth of the Amazon River in Brazil. The sharks had remained undetected because they stayed so deep, between 650 and 3,300 feet, that they were not caught in fishing gear.

There is more plankton in warmer waters, scientists said — but it would be abundant enough off Florida, so there would be no reason to visit Brazil. Gregory B. Skomal of the Massachusetts Division of Marine Fisheries said there could be another reason drawing the sharks south. Female sharks could be giving birth and raising young in tropical waters.

“We’ve never seen pregnant females, and we’ve never seen a newborn basking shark,” he said — and that could be because they haven’t been looking in the right place. Skomal said the data could be used to add protections for the sharks in the newly discovered habitat.

Remember, the third week of July is “Shark Week” on The Conservation Report

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