"The results seem confronting when you hear them up front - the thought of US$616m dollars' worth of illegal fish is staggering," FFA director general James Movick said.

He said the study would help the FFA - a Honiara-based organisation that helps regulate fishing in the waters of 17 Pacific nations - to combat the problem of illegal fishing.

Island nations typically have huge territorial waters but limited resources with which to monitor fishing activity.

Palau has only one long-range patrol boat to police an area of 500 000 square kilometres, roughly the size of Spain.

The report found the bulk of illegal fishing was carried out by trawlers which are licenced to operate in Pacific waters.

It said they either under-report their catch or transfer it to another vessel out of sight of monitors.