The three foreign ships caught poaching toothfish in the Southern Ocean are not flagged to Equatorial Guinea as they claimed.
The navy ship, HMNZS Wellington, was shadowing the vessels but has now left the area, after its crew was refused permission to board.
Foreign Minister Murray McCully spoke with his counterpart in Equatorial Guinea today, who revealed the illegal ships were not registered there.
Mr McCully said two of the vessels claimed to be owned by a likely-shell company, Stanley Management, which shared an address with a law firm in Panama.
He said New Zealand officials have contacted authorities in Panama about investigating that link.
Mr McCully said New Zealand was also working closely with Spanish authorities as two of the vessels also had links to the Spanish-based syndicate, Vidal Armadores.
HMNZS Wellington had intercepted two foreign fishing boats in the area last week - the Kunlun and the Songhua.
The Wellington also caught another ship this week - Yongding - which was thought to be part of the same fishing syndicate.