Mystery Solved: Where a Giant Basking Fish Winters

Basking shark. Photo by Chris Gotschalk
Every autumn and winter the world’s second-largest* fish, the basking shark, pulls a disappearing act. The sharks, which can grow to be 40 feet long, were thought not to stray beyond the temperate waters of the Atlantic and Pacific oceans. So scientists had no idea where the filter-feeding creatures wintered—though some posited that they hibernated on the seabed. Now, scientists have made a startling discovery: The sharks actually make long migrations, traveling from feeding areas off the coast of New England to the Caribbean, even crossing the equator and into the Southern Hemisphere. Once they reach their southern destination, they plunge to depths exceeding 3,000 feet, where they remain for weeks or months.

Using satellite-tracking tags and a novel geolocation technique, researchers traced basking sharks and uncovered their secret seasonal migrations. Led by Gregory Skomal, of the Massachusetts Division of Marine Fisheries, the team tagged 25 basking sharks off the coast of Cape Cod during the summer with a special kind of device that automatically falls off the animal and pops up to the surface, relaying its movements for an average 203 days. They published the findings in the current issue of Current Biology.

The IUCN lists basking sharks as vulnerable, one step from endangered, and notes that they are extremely sensitive to overfishing, in large part because of their slow growth rate (the sharks themselves subsist entirely on plankton). The Times explored the conservation implications of the findings:

*The largest fish is the whale shark.