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:
|A meeting of basking shark specialists in August aims to kick-start worldwide photo-identification and DNA profiling of the sharks to help to establish the extent of their migrations. The work may solve another mystery. Scientists had believed that there were four species of basking sharks, but the new discoveries, published yesterday in the journal Current Biology, suggest the global population of about 10,000 may be a single species.
The news that the sharks may be a single population has dramatic implications for their conservation. Although basking sharks are protected in European waters, shark liver oil is still used in cosmetics, lubricants and traditional Chinese “medicine”, while fins are taken for shark-fin soup.
A six-tonne basking shark can yield a two-tonne liver. When that is combined with the price of their fins — up to $50,000 on Asian markets — the need for an international shark management plan is clear.
*The largest fish is the whale shark.