"Italy's illegal activity in the Mediterranean bluefin tuna fishery is not just a threat to this magnificent species, but also jeopardises the future of those trying to fish this resource in a sustainable and legal way," said Michele Candotti of WWF, formerly the World Wildlife Fund.

Italy has launched legal proceedings against the European Commission for curtailing the hunting season and says it did not reach its tuna quota this year due to the European ban which also applies to Cyprus, France, Greece, Malta and Spain.

The EC said in June that some Italian tuna fishing vessels exceeded their quota by between 100 and 240 percent this year.

Bluefin tuna are known for their huge size, power and speed, with maximum weights recorded in excess of 600 kg (1,300 lb). Since last year, market prices for the delicacy have tripled: in Japan a single fish can cost up to US$100,000.

WWF analysed trade data and used aerial surveys to monitor Italian fishing activities. It says spotter planes were reularly used to help fish the tuna -- a practice which has been outlawed, and that many Italian tuna catches were not recorded.

WWF said it would present its findings to the Commission and to the International Commission for the Conservation of Atlantic Tunas (ICCAT), which sets quotas and is due to meet next in November to review conservation measures.

WWF is calling for a moratorium on bluefin tuna hunting to allow stocks to recover from what it says are levels that endanger the species' survival.

It is also asking consumers, retailers and restaurants to boycott the fish which is a prized delicacy, especially in sushi and sashimi dishes where cuts are often known as toro or maguro. (Reporting by Robin Pomeroy; Editing by Louise Ireland)