Is this the end of the bluefin tuna?

They are among the most legendary and majestic fish in the sea – and beyond doubt the most valuable. A decision taken this week, however, means that the bluefin tuna of the Mediterranean are probably now also the most endangered fish in the sea, with overfishing pushing the stock towards the brink of collapse.

Celebrated since the time of Homer, the mighty and meaty bluefin these days have ardent admirers on the other side of the world: the Japanese, who prize them above all other fish for use in sushi and sashimi. But so great is the Japanese demand that it is driving catches well beyond what scientists consider to be safe limits and towards commercial extinction.

Earlier this week, however, a vital opportunity to pull the bluefin back from the brink was missed when the official body charged with preventing the stock from collapsing agreed to allow catch quotas for 2009 far higher than its own scientists recommended.

Amid a chorus of protests and dismay from conservationists, the International Commission for the Conservation of Atlantic Tunas (ICCAT), meeting in Marrakech, Morocco, endorsed a total allowable catch (TAC) of 22,000 tonnes for next year – while ICCAT's own scientists had recommended a TAC ranging from 8,500 to 15,000 tonnes per year, warning there were real risks of the fishery collapsing otherwise.

The scientists also urged a seasonal closure during the fragile spawning months of May and June, but the meeting agreed to allow industrial fishing up to 20 June.

The decision, which was branded "a disgrace" by the World Wide Fund for Nature (WWF) and fiercely attacked by other conservation bodies, was driven by the European Union, amid allegations that the EU had threatened developing nations with trade sanctions if they supported lower catch limits and extended closed seasons. During the meeting, the names of some countries appeared and disappeared from the more scientifically based proposals.

The EU is representing the interests of several countries who have big fishing fleets hunting the multi-million-dollar bonanza that the annual catch represents. In the lead are the French, with about 600 tuna boats, followed by the Italians, who have a fleet of about 200 vessels. It is thought that half the Italian fleet may be unlicensed boats, especially those from Calabria in southern Italy, and Sicily, where Mafia connections to some of the fishing operations are strongly suspected. Algeria, Croatia, Greece, Libya, Malta, Spain, Morocco, Tunisia and Turkey are other countries with tuna fishing fleets.

The hunt is based around the spawning habits of a specific subspecies of the bluefin tuna, the eastern Atlantic bluefin, which swims every May from the Atlantic, where it spends the winter, through the Straits of Gibraltar to spawn in June and July in the warmer waters of the Mediterranean. The migration takes place in huge schools of fish which, in the past, were miles wide and millions strong – and even with today's depleted numbers it can still be a remarkable spectacle. Spawning sites, where the females releases millions of eggs at night, are scattered from one end of the Mediterranean to the other.

Intercepting the huge shoals has been done for thousands of years but, in recent years, advances in fishing technology, as well as demand, have made the contest entirely one-sided. ICATT has established rules for the fishery but conservationists claim they are being consistently broken by the hunters. For example, the use of spotter aircraft to locate the tuna shoals has been banned in the month of June since 2001 but such spotter planes have been seen operating from Libya, Malta and Italy. Similarly, drift nets have also been banned but Italian fishermen have been found to be using them.

But the most serious and frequent malpractice is exceeding catch quota limits, which is thought to happen with all countries involved in the fishery. For example, the French this year had a quota of 4,300 tonnes but are thought to have caught about 7,000 tonnes. Most of the catching is done with purse-seines, which are very large bag-like nets capable of scooping up an entire tuna school. The purse-seines allow the tuna to be taken alive and transported to tuna ranches – there are about 40 scattered about the Mediterranean – where they are fattened for the Japanese market. The greater the fat content of the fish, the higher the price the Japanese will pay. They are slaughtered in the autumn and freighted to Japan.

The tuna ranching is driven by Japanese demand, which in turn, say conservationists, is driving the overfishing. The meeting at Marrakech had a chance to bring the fishery back under control, but the decision, taken by politicians with powerful fishing groups in their constituencies, went the other way. It was fiercely attacked by groups such as WWF. "This is not a decision, it is a disgrace which leaves WWF little choice but to look elsewhere to save this fishery from itself," said Dr Sergi Tudela, head of the WWF's Mediterranean fisheries programme.

The Green Party group in the European Parliament also lashed out at the decision. "The ICCAT quotas are a death sentence for the bluefin tuna," said the Green Party MEP Raül Romeva, who attended the meeting. "It is completely unacceptable that the body responsible for managing stocks has set a TAC that is 50 per cent higher than the scientific advice. The EU had pressed for even higher catches. It is morally bankrupt for [the EU Fisheries] Commissioner Joe Borg to make noises about the need to conserve bluefin tuna before the ICCAT meeting, when the European community then proceeds to use strong-arm, bullying tactics to try to impose a maximum total catch two-thirds higher than the scientific advice.

"The EU has bankrolled the decimation of bluefin stocks by subsidising the new large fishing vessels that are responsible for overfishing, to the detriment of certain traditional fishing fleets. When the stocks are gone, the same ship owners who lobbied to overexploit bluefin tuna will come cap in hand for more EU money. This must not be allowed to happen."