The sight of a basking shark’s brooding silhouette gliding through the waters off western France is more than just a rare treat for sailors — it is a boon for scientists trying to trace its secretive migrations across the globe.
It may be the world’s second largest fish, growing to more than 10 metres, but the basking shark, or Cetorhinus maximus , is an enigma for scientists eager to help preserve the plankton-eating giant after centuries of overfishing.
Hunted voraciously for its massive fin — highly prized for sharks’ fin soup in China — as well as its oily liver and meat, global population of basking shark declined precipitously during the 20th century. The species has struggled to recover because of slow reproduction rates.
While the sharks have captured the imagination of sailors for hundreds of years — some think early seafarers mistook the massive sharks swimming in single file for sea monsters — crucial details about their behaviour remain elusive to researchers.
“It’s a shark that remains very mysterious,” said Alexandra Rohr of the research group APECS, which is based in the Brittany town of Brest and dedicated to the study of sharks, skates and rays.
Tagging the sharks
Even population estimates, the age of sexual maturity and where and when the sharks reproduce are not known for certain, Mr. Rohr said.
They are spotted more frequently during the summer months while in winter they all but vanish from view, leading to theories that they migrate to warmer regions or dive down into the ocean depths.
Using new tracking technology, APECS researchers monitoring sharks when they are near the water’s surface have discovered evidence of a much greater migratory range than previously thought.
One tagged female was tracked off the coast of northern Scotland on September 20, 2016, and then resurfaced four months later south of the Canary Islands. By May 2017 the shark was back in the Bay of Biscay, south of Brittany.
APECS also relies on crowd-sourced information from divers, sailors and other members of the public. Alain Quemere sighted a basking shark during a fishing trip in the Glenan archipelago and reported details to APECS, enabling a research team to track and fit it with a satellite tracker.
