A senior Australian fisheries official said Japan had illegally taken A$2 billion ($1.53 billion) of prized southern bluefin tuna over the past 20 years in breach of quota restrictions, local media reported on Saturday.
An investigation found Japanese fishermen and suppliers from other countries caught up to three times the Japanese quota each year for 20 years, the Sydney Morning Herald reported the official as saying.
Australian Fisheries Management Authority managing director Richard McLoughlin made the comments in a seminar to students at the Australian National University on August 1, which was later posted on the internet, the paper said.
"It's just been revealed that ... on a 6,000-tonne national quota, Japan's been catching anything between 12,000 and 20,000 tonnes for the last 20 years, and hiding it. And that has probably killed the stock," the paper quoted him as saying.
Quotas for each season's southern bluefin fishing are allotted by the Commission for Conservation of Southern Bluefin Tuna, comprising Japan, Australia, New Zealand, Taiwan and South Korea. The total 2005 quota was 14,080 tonnes, while Japan's quota was 6,065 tonnes.
The newspaper said the overfishing figures were contained in a report that was presented at an international meeting in Canberra in July, but which remained confidential.
One of the world's most expensive fish, southern bluefin migrate around the temperate waters of southern Australia and grow to about 200 kilograms. McLoughlin later told the newspaper he had nothing to add to his comments.