TOKYO (AFP) - Japan plans to propose a 50 per cent cut on catches of young bluefin tuna in the Western and Central Pacific, officials said on Tuesday, in a historic shift aimed at safeguarding the at-risk species.

Tokyo - the world's biggest consumer of tuna - has been reluctant to reduce catches, despite mounting scientific evidence that stocks are near collapse.

But in what it called "an epochal move towards more thorough regulation", Japan plans to propose during an upcoming regional fisheries conference that the amount of young fish that can be caught is slashed to half the 2002-2004 average.

Japan said it would propose members of the Western and Central Pacific Fisheries Commission (WCPFC) adopt a 10-year recovery plan for Pacific bluefin tuna, beginning in 2015.

The plan would see the amount of young tuna - defined as those weighing less than 30kg - that Japan is able to catch cut to around 4,000 tons a year.

During a four-day meeting scheduled to take place in Fukuoka, western Japan, from September 1, Tokyo will also suggest a warning system intended to help stem overfishing.

Under the system, warnings or alerts will be issued to local fishermen as soon as authorities notice that bluefin tuna catches are approaching pre-set ceilings, the officials said.

When the catch reaches 95 per cent of the alloted amount, the government will ask fishermen to suspend operations, the officials said.

"Bluefin tuna is virtually the main resource in waters around Japan. Japan must take the lead in protecting that resource," said Masanori Miyahara, president of Japan's Fisheries Research Agency, during a meeting with tuna fishermen in Tokyo.

The shift in Japan's policy towards more radical conservation comes after an international independent assessment found last year that stocks of bluefin tuna, prized by sushi lovers, had fallen 96 per cent from their original levels.

Young fish form the majority of specimens now being caught, pushing the species closer to extinction, it said.

"We give credit to the Fisheries Agency for finally taking serious action as it had done virtually nothing beforehand," Greenpeace Japan's Wakao Hanaoka, an expert in marine ecology, told AFP.

"But we have to say that its actions are still not enough because bluefin tuna could make the list of endangered species any time."