Fragile shark populations are being devastated by a “wall of death” laid by European fishermen, Westcountry scientists and conservationists have warned.
Up to four million sharks, mainly blues and makos, are estimated to be caught every year in the north Atlantic as fishermen target migratory routes to and from British waters.
It is feared long-line fishermen from Spain and Portugal are targeting sharks after a collapse in tuna catches.
The extent of the problem has been revealed by researchers from Plymouth’s Marine Biological Association (MBA) which tagged and tracked 100 sharks and compared their movements with those of almost 200 long-line vessels.
David Sims, professor of marine ecology at the MBA, said they had identified areas which attracted both sharks and fishermen.
“We found that the sharks are congregating where warm and cool currents meet,” he said. “These are highly productive areas that attract fish and that attracts sharks too.
“However, it also attracts fishing vessels and we found many long lines laid in exactly the places where sharks concentrate. It is a wall of death for sharks.”
The scale of shark catches – some 100 million are thought to be killed around the world every year – has long concerned conservationists.
Many shark species take years to mature, have a long gestation period and give birth to few young.
It has meant populations have been dropped alarmingly, with the species being unable to repopulate after being targeted for its meat and fins.
One species – the porbeagle – is thought to have decreased by more than 90 per cent since the 1930s.
With populations in the north-east Atlantic and Mediterranean listed as critically endangered, porbeagles now have protection under the Convention on International Trade in Endangered Species.
However, the commercial fishery, which uses baited lines strung out for up to 60 miles long, is largely unregulated. One major market is in the Far East where shark fin soup is an expensive delicacy.
“We know shark populations are plummeting but we didn’t know why,” Prof Sims said. “Was it fishing or something else?
“We needed to know how much their range overlapped with fishing boats. what we found was a 76% overlap, so it is clear that these long-liners are having a major effect.”
Data from satellite tags fixed to sharks’ fins was set against information from the log books of two Spanish fishermen over the last 16 years. Ship movement data was also provided by the Spanish and Portuguese governments.
Ali Hood, director of conservation for the Plymouth-based Shark Trust, said landings of blue sharks reported by the EU fleet had tripled since 2003, with Spain responsible for more than 80%.
While the EU is introducing management for some of the most vulnerable species, she said, blue shark, shortfin mako, smoothhounds and catsharks could all be caught in unlimited amounts.
“Seeing the intensity of the long-line fleet’s activity mapped out is shocking, but unfortunately does not come as any great surprise”, said “The EU fleet has increasingly focused its efforts on the Atlantic, now the source of over 88% of reported EU shark landings.”
“As landings increase year on year, and with no science-based catch limit in place – it is imperative that those countries responsible for these landings and the associated regional fisheries management organisations seek to control shark fishing now,” said Hood.
“The trust believes that when the public understands the sheer scale of mortality they will want to add their voice to this campaign – No Limits? No Future.”