Five tuna species are classed as "threatened" or "near threatened" with extinction due to overfishing, according to the Red List of Threatened Species, prompting environmental groups to plea for fewer industrial-scale boats.

As big players in the multi-billion dollar industry gathered for a trade conference in Bangkok, Greenpeace urged tuna brands to source fish sustainably and end "destructive" fishing methods that see other marine life caught.

"It's an urgent situation. There are simply too many boats... there needs to be a radical cut if we are going to reverse the decline in stocks," Sari Tolvanen, a campaigner with the environmental group, told AFP.

"You would think the industry would be concerned about declining stocks, but it's sitting on its hands."

Greenpeace says tuna populations can rebound if they are given adequate protection.

The group wants a ban on "fish aggregating devices" that lure marine life into vast bucket-like nets with the result that 10 percent of each catch is made up of species other than tuna.

The tuna industry -- from the factory-sized boats to supermarkets -- says it recognises the problem of dwindling stocks and follows quotas limiting catch to mature fish in waters where stocks are abundant.

The Atlantic bluefin species, which can live until they are 40 years old and grow to more than four metres (13 feet) long, is in the gravest danger of disappearing.

It is so highly prized by sushi-loving Japanese that a 269-kilogram (592-pound) fish went for a record 56.49 million yen ($737,000 at the time) in January auctions.

International agreements to tighten fishing controls are coming into effect, with the European Union, whose waters provide 60 percent of the global haul, this year pledging to protect the endangered bluefin by slashing quotas.

But they can do little to prevent illegal fishing of at-risk species, which also include bigeye, classified as vulnerable, along with yellowfin and albacore, both ranked as near threatened.

Five main species of tuna make up the annual worldwide catch of 4-4.5 million tonnes.

Destined mainly for supermarket shelves, the abundant skipjack accounts for 60 percent of the total.