The captains of two Korean fishing vessels and their on-shore manager are to be fined $360,000 for filing false catch reports.
The Korean boats were working under a permit issued to a Tauranga-based company.
The Ministry of Fisheries says it decided to look into the matter after discovering irregularities in the vessels' usual fishing patterns.
Investigations late last year found the commercial boats had been fishing off one part of Stewart Island and then reporting the catch as having been made in another area.
The ministry says its analysis of the first suspicious trip revealed that six previous catches had also been falsely reported.
It says the practice, known as 'trucking', is common, and has a huge effect on the sustainability of fish stocks.