In what Australian officials called an outrageous fraud, Japanese fishers probably used a series of disguises for the overcatch and international investigations have found.

The fishers described southern bluefin tuna as a different species and evaded any inspection on shore, underreported the amount of the fish they caught, and imported it as different tuna either transhipped at sea from foreign vessels or in containers. In a review that the Japanese government has vetoed from public release, investigators found the fraud extended to consumer markets.

While diplomats meeting in Canberra in October heard that Japan's figures still do not add up and that the estimated total overcatch is probably at 10 per cent more, Tokyo keeps stonewalling attempts to regulate fishing of the critically endangered species.

Attempts to introduce a catch documentation scheme and a binding international paper trail to track all catches has made very little progress at the conservation commission. No agreement could be reached on a satellite tracking system for southern bluefin boats or on having independent observers on board.