Nobu keeps endangered bluefin on the menu but asks diners to choose an alternative

The concession comes after a lengthy campaign by environmentalists to persuade the global chain of Japanese-South American fusion restaurants to stop selling bluefin tuna dishes.

In response, Nobu, whose London branches in Park Lane and Berkeley Street sell bluefin in a variety of forms, in dishes costing up to £32 each, has now put a footnote on its menus and website saying: Bluefin tuna is an environmentally threatened species please ask your server for an alternative.'

Highly prized by sushi fans, bluefin tuna commands stratospherically high prices, particularly on the Japanese market, where one fish can sell for $100,000. But demand is such that stocks in the Atlantic and the Mediterranean have fallen dramatically in recent years.

WWF, the former World Wildlife Fund, which estimates that breeding stocks could disappear by 2012, has criticised Nobu's move. Giles Bartlett, its senior fisheries policy officer was reported as saying: They shouldn't sell endangered species. They should change their menu to incorporate a fish that's sustainable and not one that's critically endangered.''

Nobu is one of the few major restaurants that continues to sell bluefin, although it still does not specifically state on its London menus that its tuna is bluefin, despite a commitment to do so by one of the chain's backers.

Last year, Greenpeace investigators were told by serving staff in London that their tuna was not bluefin, but tests on samples smuggled out of the restaurants proved otherwise.

Richard Notar, the chain's New York-based managing partner is quoted in a new film about endangered fish species saying it was "unacceptable" that customers were not being told the truth.

He said that he would like to take bluefin off the menu, but it was being resisted by his Japanese chefs. The company is also exploring using bluefin farmed in Australia.

Mr Notar said that in future its menus would distinguish between bluefin and less endangered species of tuna like yellowfin. This is now the case in its American outlets, although they do not carry the advisory footnote.

The restaurant's novel way of dealing with the issue features in documentary The End of the Line, based on the book by environmental journalist Charles Clover, which is released next month.

Mr Clover has spent several years trying to persuade Nobu to speak about its policy on sustainability. Among a range of tuna dishes it sells o-toro tuna sushi – the most prestigious cut of meat – for £8 for a single piece.