"Japan absorbs between 90 and 95 percent of catches of red tuna and the Mediterranean version is especially appreciated," explains Jose Luis Garcia, head of the WWF oceans section.

The price of a prize red tuna can top 50,000 euros (60,000 dollars) on the Japanese market.

"In opening new markets, exploitation (of stocks) has been pushed even further," Garcia said, alluding to the growing international taste for sushi.

Ecologists want to highlight the threat in the run-up to a meeting in Croatia of the International Commission for the Conservation of Atlantic Tunas (ICCAT).

And they have made common cause with small-scale fishermen who see industrial-scale practices ravaging the stocks on which they base their livelihood.

The international commission is to reevaluate annual fishing quotes for the first time since 2002, which are currently fixed at 32,000 tonnes for the "western Atlantic" zone.

Prior to the November meeting ICCAT scientists are going to meet in Madrid from June 12 to 18 to draw up a list of recommendations.

Greenpeace and the WWF hope to make their own voices heard.

"In 2002, scientists recommended 22,000 tonnes, but ICCAT decided to give 10,000 tonnes more," says Garcia.

Even this generous quota has been exceeded, say environmentalists, who claim the overall catch in 2005 hit between 40,000 and 50,000 tonnes due to fishermen overraiding stocks.

"This time we want to see the quotas come down enormously in response to the crisis," says Garcia.

The environmentalists are not targetting the small-scale fishermen who use nets according to local custom, but industrial flotillas and their high-tech operations.

With boats guided by satellite and planes that circle above banks of tuna during the breeding season, they capture thousands at one go before taking them to tuna farms to be fattened.

The centres, which receive large-scale EU subsidies, are farms in name only as they do not practise any kind of aquaculture, red tuna being unable to reproduce in captivity.

In contrast, the traditional fishermen in the Bay of Cadiz of southwestern Spain practice an age-old system of netting migratory tuna.

"Almadraba" is a spectacular method dating back more than 3,000 years to Phoenician times. The fishermen set out from the beach to cast out nets that go down as far as 23 metres (yards).

When the tuna appear in sufficient number on their migration across the Strait of Gibraltar to reproduce in the Mediterranean, the fishermen draw up the nets and haul their enormous catch aboard.

Many of the Almadrabas fishermen have today disappeared from the Mediterranean, environmentalists note, lamenting the demise of a method which respects the sea and its fauna.

Those fishermen who do remain have joined forces with the ecologists after being made victims of overfishing.

In the Strait of Gibraltar and the local ports of Barbate, Zahara de los Atunes, Tarifa and Conila, the tuna season which opened in April is about to come to an end.

It has not not been a prosperous one.

By late May only 3,787 tuna had been caught, down from 8,390 in 2000 -- "a disaster," according to Marta Crespo, who manages the local fishing organisation.

Only the best-placed survive around Cadiz, where the tuna hug the coast to avoid the strong currents common to the middle of the strait.

At Barbate, freezer ships from Japan come to load up the merchandise directly. The choicest pieces, such as the exquisite flesh from the tuna's stomach, will be dispatched by plane from the tiny local airport, to be served up as a delicacy, only hours later and across the world.

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