BARBATE, Spain, Oct 1 (Reuters) Fishermen like Diego Crespo have trapped the giant tuna swarming into the warm Mediterranean for over 3,000 years, but he says this year may be one of his last.
Japanese demand for its fatty flesh to make sushi has sparked a fishing frenzy for the Atlantic bluefin tuna -- a torpedo-shaped brute weighing up to half a tonne that can accelerate faster than a Porsche 911.
Now a system of corralling the fish into 'tuna ranches' has combined with a growing tuna fishing fleet to bring stocks dangerously close to collapse, warn scientists from ICCAT -- the body established by bluefin fishing countries to monitor the stock.
''There are plenty of signs that we might be seeing the start of the collapse,'' said Susana Sainz, a fisheries officer with campaign group WWF.
The environmental impact would be catastrophic, she said: ''The bluefin is a top predator so the whole ecology of the Mediterranean would be destabilised.'' Tuna has become a big business throughout the Mediterranean, and the lure of up to ,000 for the best and biggest fish attracts dozens of new boats to the industry every year -- many controlled by Asian and Italian mafias, sources say.
That in turn depresses prices and compels fishermen to break catch limits.
''IT'S OVER'' Over-exploitation, pollution and climate change have devastated many of the world's commercial fish stocks and campaigners say a UN agreement to restore them by 2015 fails to set strong enough targets.
Some campaigners say it may already be too late to save the bluefin after high-tech fleets -- many guided by illegal spotter planes -- this season converged on an area near Libya that had been considered one of its last refuges.
''It's over, that's my gut feeling from both a stock point of view and a business point of view,'' said Roberto Mielgo Bregazzi, a fisheries consultant who set up the first 'tuna ranches' 10 years ago.
The ranches -- giant underwater cages where freshly caught tuna are fattened on squid and sardines -- have revolutionised the industry.
The innovation allows fishermen to scoop up shoals of spawning tuna, transfer them to the 50-metre-wide cages and return to fish until the last is caught.
Deep-frozen and shipped to Asia, the bulbuous carcasses are sold in auction rooms like Tokyo's Tsukiji market before the red meat is sold for up to 75 dollars per 100 grams when served in the city's best restaurants.
Crespo said he soon felt the impact of tuna ranching on his and other fixed trap nets known as 'Almadrabas' -- a labyrinth of nets that fishermen have anchored in the shallows of Spain's south Atlantic coast since pre-Roman times.
''For the last seven or eight years we've seen a drought in the catch,'' Crespo said as he walked between mountains of net and cable spread about his warehouse in the fishing town of Barbate, on the Costa de la Luz, south of Cadiz.
His employees spend two months setting up the complex system, then wait for the tuna to arrive in April. Every few days fishermen corral the net and hoist it to the surface, while others jump into the thrashing mass of silvery fish to hook and haul them aboard.
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