Figures reported to the United Nations Food and Agriculture Organization put the number at 0.4 to 0.6 million tonnes a year.
“Our findings confirm that a far larger number of sharks are being caught every year than current databases indicate. The fin trade is continuing to expand and thus the pressure on shark populations is constantly increasing,” said Dr Shelley Clarke of Imperial College London.
Species most at risk are the blue shark, hammerheads and silky sharks, according to the researchers.
They said official estimates of the number of sharks killed each year may not reflect the true figure because many fish are caught by unregulated fisheries which do not report the catch.
The findings reported by the scientists in the journal Ecology Letters, are based on an investigation of shark fins sold at auction in Hong Kong, which is the world’s largest fin market.
The World Conservation Union says 65 out of 373 known shark species are threatened, largely because of the trade in shark fins. Some experts think the number is higher.
Several countries have banned the slaughter of sharks for their fins following public outcries.
Sharks are among the ocean’s most threatened animals mainly because of over fishing. They grow slowly, mature late and produce few young which makes them particularly vulnerable, according to the Shark Alliance, a coalition of non-governmental organisations dedicated to shark conservation.
Image: A grey shark at the Sea Life aquarium in Roquetas del Mar, southern Spain. REUTERS/Francisco Bonilla