The Royal New Zealand Navy has discovered a third fishing vessel with illegal catch in the Southern Ocean.
Foreign Minister Murray McCully said this afternoon that the HMNZS Wellington had intercepted a ship called the Yongding to the west of the Ross Sea near Antarctica.
It was believed to be linked to two other fishing vessels which were intercepted by the navy yesterday, the Songhua and the Kunlun.
Defence Force officials have gathered photographic evidence of the ships using banned fishing methods.
The Songhua and the Kunlun vessels were also on an illegal fishing blacklist set up by the Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR).
Mr McCully said the three ships claimed not to be part of a group but had been observed operating alongside each other.
"This strongly suggests they are part the same illegal fishing syndicate," he said.
The minister said two of the vessels had previously been linked to the Spanish-based syndicate Vidal Armadores SA.
All three of the ships claimed to be flagged to Equatorial Guinea.
Government has contacted that country's government to "convey its concerns" and to request permission to board the vessels but has so far had no response.
Environmental activist group Sea Shepherd, which was also conducting patrols around Antarctica, has reported that there were six ships currently poaching toothfish in the precious, strictly regulated Southern Ocean fishery.
CCAMLR set quotas for the fishery and regulated how and where fish could be caught. The Songhua and the Kunlun had been blacklisted for breaching these rules.