There are expected to be further investigations into a number of boats following a region-wide maritime surveillance operation in which three were apprehended.
A total of 24 vessels were identified in Operation Kurukuru as being involved in suspicious activity.
11 countries participated in the surveillance with patrol boats and planes investigating more than 220 boats operating in the Pacific's exclusive economic zones.
Commander Bill Triffit of Australian Maritime Surveillance says Tonga co-ordinated the operation and it was kept secret in order not to alert fishing fleets.
He says many boats were complying with the law but a significant number weren't.
"Out of the roughly 220 vessels that we looked at, we found that about 24 of them were potentially conducting illegal activities and of those, about 12 of them were of real concern. So, I suppose we have found, so far about 5 percent of the vessels at least so it is a significant problem."
Commander Bill Triffit.