Rare yellowfin tuna makes second ever visit to British shores

In a week when 6ft swordfish and porbeagle sharks have arrived off the Northumberland coast, further evidence of Britain's warmer waters has arrived with the landing of only the third bigeye tuna to be caught off British shores.

The 40lb specimen, one of the most highly prized species of tuna, is usually found off the coasts of Hawaii and Australia where it is generally preferred to the almost indistinguishable yellowfish tuna by discriminating purveyors of sashimi and sushi. But this one was caught by a Penzance-based fishing vessel in the Atlantic - 70-miles off Land's End and 2,000 miles adrift of its usual habitat. It was promptly sold for £90 to a fish dealer at Crowlas, on the Cornish coast.

The only other known bigeye catches have been at Newlyn harbour in Cornwall, where a 15-year-old boy fished one out in 1985, and at Christchurch Bay in Dorset in 2004. But the south-western tip of England is becoming accustomed to new arrivals. Giant ocean sunfish were recently recorded for the first time by scientists who counted 19 of the species while conducting an aerial survey of coastal marine life in the area around Land's End from Falmouth to Newquay. Basking sharks have also ventured closer to land than ever before, attracted to an abundance of algae, jellyfish and smaller fish which thrive in the warm waters. Experts are even debating the existence of great white sharks off the Cornish coast. A BBC documentary last weekend reported alleged sightings by a number of holidaymakers and fishermen.

The bigeye (thunnus obesus), which is commonly mistaken for the yellowfin because of the similar yellow markings on its fin, exists in tropical and subtropical waters of the Pacific, Indian and Atlantic oceans where the surface temperature exceeds 17C (62F). The nearest areas to Britain in which it is commonly found are the Azores - though the world's biggest suppliers are Japan, Taiwan, Spain and Korea.

"It certainly is very, very rare and it is one of a number of sightings of unusual warm-water species, which is very interesting," said Matt Slater, curator at the Blue Reef aquarium in Newquay. "There was a fleet of tuna boats that used to fish out of Newlyn but they used to fish a long way down in southern Spain and the Atlantic. There is a huge amount of evidence to show that the warmer water species are coming up here. Water temperatures are rising."

Douglas Herdson, of the National Marine Aquarium in Plymouth, said: "Global warming is often raised as the cause for the sightings but, to be honest, we don't really know why it has come to these waters. When there is just the one fish turning up it is more likely that it has just wandered off course from its shoal in the search for food."

The trade buyer, Julian Smart, expected to make a handsome profit from the fish, which will make 50 meals when passed on to a distributor in London. "It was a lovely specimen," he said. "There was no damage from the net, it was bright eyed and very firm. It is good to be able to provide our customers with something different because there is that rarity value."

But restaurants' demand for the bigeye - which has a dark metallic-blue back, a grey-white belly and iridescent blue bands running along each flank - have made it one of many species considered by Greenpeace to be vulnerable and under immediate threat of over-exploitation.

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