But four years ago a few Cornish fishermen joined the French and Irish in purchasing drift-nets and seeking shoals of the migratory fish in the Bay of Biscay.
The Basque fishermen of Spain had been fishing the tuna for years using long lines hung off rods with baited hooks attached. According to a European Commission report they took 28,000 tonnes in 1987, while the embryonic French and Irish drift-net fleet caught just 150 tonnes.
By 1992, the Spanish catch had sunk to 18,100 tonnes while the French and Irish took just under 5,000. When the tuna migrated into the bay this summer, the Spanish resorted to violence.
Their boats blockaded their own northern ports for four days last month, and also blockaded a French border port. The action disrupted ferry traffic with Britain, stranding or delaying more than 3,000 tourists.
So far, the British boats have got off relatively lightly. Last month, the French trawler La Gabrielle was rammed and pelted with petrol bombs after 60 Spanish boats surrounded five French vessels 450 miles out to sea.
The Spaniards say they have acted each time because the other fishermen have been using drift-nets longer than the 2.5 kilometres (1.6 miles) which European Union law has allowed since 1991. Until the beginning of this year, the French had reserved the right to use longer drift-nets although they have now come into line with the rest of the EU.
There is intense mistrust between the rival fleets. Each nation's own government inspectors are meant to ensure the rule is being complied with; the Spanish believe the French, Irish and British inspectors are turning a blind eye to cheating.
Two weeks ago, EU fishery ministers agreed to give the commission's own small force of fishery inspectors greater powers to check for overlong drift-nets. This move does not seem to have ended the mistrust.
Alan Laurec, a fisheries conservation official with the commission, said yesterday that the four inspectors deployed in the North East Atlantic were not allowed to stay on fishing boats nor to measure drift-nets directly. Instead they go on the member government's fishery patrol vessels. 'They inspect the inspectors. This year infringements have been shown for some French vessels and one Irish boat.
'The risk is that if the rules are not implemented the fishermen who say they are suffering will do the policing themselves. That's what has been happening.'
There is an irony in the Spanish crying foul. Along with the Portugese, they are regarded as pirates with a cavalier attitude towards the rules. Their deep-sea fleet ventures thousands of miles from home, exploiting one stock after another.
The Cornish fishermen turned to tuna and invested tens of thousands of pounds in drift-nets after quotas and the incursions of foreign boats - including Spanish ones - had undermined the profits from their traditional white-fish catch. Up to 10 boats participate and they landed 780 tonnes last year.