Protected by British and international conservation agreements, basking sharks are regularly seen off the coast during the summer, but very little is known about where and how they live for the rest of the year, researchers at the University of Exeter said.
More than 81,000 were killed in the northeast Atlantic Ocean between 1952 and 2004, hunted largely for their liver oil.
University researchers, along with the Marine Conservation Society, Cornwall Wildlife Trust and Wave Action, analyzed 20 years of public sightings -- a total of 11,781 records -- and boat-based basking shark surveys to complete the largest study of its kind.
Sightings from the 1980s through to the 2000s revealed an increase in the proportion of medium and large-sized animals, suggesting an increase in the number of older sharks. Basking shark populations are believed to recover slowly from over-exploitation due to their slow growth to maturity and the relatively few offspring they produce in comparison to other fish species, researchers said.
Analysis of sightings suggests long-term protection may well be paying off, they said, with British basking shark populations showing increasing body size, a classic sign of recovery for over-exploited fish stocks.
"Our research shows that basking sharks could be recovering from the extensive hunting that took place in the 20th century," Exeter researcher Brendan Godley said. "Anyone who has had the experience of seeing a basking shark from our coastline will know what awe-inspiring creatures they are and our research suggests that more of us may be fortunate enough to see them in the future."