One of the Royal New Zealand Navy's (RNZN) Offshore Patrol Vessel's (OPV), deployment to the Southern Ocean. The Yongding and Kunlun Vessels in the same area

A boat snared poaching in the Southern Ocean was detained after docking in Thailand with 180 tonnes of toothfish.

The Kunlun arrived in Phuket on Monday and attempted to offload what it claimed was groper. Previously registered to Equatorial Guinea, it was falsely reflagged as an Indonesian vessel and renamed Taichan.

Bangkok-based New Zealand officials, police and customs officers arrived on the island soon after and have been working with Thai counterparts to hold the boat and its illegal haul.

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Its understood one of the heads of the notorious Spanish syndicate Vidal Armadores also travelled to Phuket after it became clear the boat was to be detained.

The Government worked quietly behind the scenes after the navy was slammed for failing to board two of a fleet of three vessels spotted poaching in Antarctic waters in January.

After tracking the Kunlun to Thailand, they alerted officials and passed on evidence collected by the HMNZS Wellington patrol.

Meanwhile, recent raids in Spain on Vidal Armadores-linked companies came after pressure from Wellington. Operation Sparrow - an investigation into alleged links with illegal, unreported and unregulated (IUU) fishing activities marked the first time Spain enforced a new fisheries law.

The rust-eaten Yongding and Songhua are still operating in the Southern Ocean.

Foreign affairs minister Murray McCully said he was able to confirm New Zealand authorities were working with Thai authorities. "This is a result of very good co-operation we have had with governments in a number of countries.

"I draw attention to my earlier remarks that we weren't going to put a stop to this business overnight but we were prepared to invest the necessarily energy to make sure we put them out of business at some point."

McCully previously fingered the poachers as Spanish pirates and named Stanley Management Incorporated, a Panama company and Sucre Arias Reyes, law firm, that he said provides a front for boats illegally fishing for the pricey delicacy.

Thailand is not due to pass domestic fishing laws until June, which left authorities with few legal options. "Two things were useful," a New Zealand government source said.

"Firstly, they'd declared the catch as groper, not toothfish. There is no question [it is toothfish]. It is an offence to declare your fish something different to what it is. That gave [Thailand] some capacity to hold for some time.

"Separately, the boat had gone in there identifying itself as the Tiachan, flying the Indonesian flag. Our guys were quick to establish with the Indonesians that they didn't own it. So, it is technically stateless, giving the Thai authorities a facet to keep the vessel held. We've been encouraging them to confiscate the catch, so they don't get any benefit from their misdeeds."

The source added the Vidal Amadores "have had their people on the ground trying to get their boat sprung."

The raids in Spain came "as a result of information being supplied to them on a continuing basis."

Antarctic toothfish is prized by top-end restaurants. They can grow up to 40kg in the remote and over-fished waters, and fetch around US$50 ($64) a kilo.