UNABLE TO BOARD: HMNZS Wellington and the vessel Kunlun in southern waters.

The navy was barred from boarding two boats fishing illegally for toothfish in Antarctic waters, which then tried to get away.

Captains of the Yongding and the Songhua have refused to let the crew board. The navy was attempting to verify the flag status of the Equatorial Guinea-flagged vessels after the Government gained permission from the central African nation overnight.

The Wellington's crew also wanted to gather evidence to use in any future prosecution after shooting video of the fishermen hauling aboard their illegal catch.

Supplied TOOTHFISHING: A crew member on the Kunlun.

In the past week they have busted three ships - linked to Spanish pirates - poaching in the Southern Ocean.

Foreign Minister Murray McCully said the Wellington's crew had a "legitimate right" to board "but the vessels refused to co-operate".

"Due to the conditions and the evasive tactics of the masters it was not possible to safely board these vessels," he added.

"While this is disappointing, it is important that we keep the safety of the New Zealand crew as our paramount consideration."

The boats are thought to be working in the freezing and remote waters for a notorious Spanish syndicate, and two of the ships have been internationally blacklisted.

The waters of the Southern Ocean, which were previously overfished, leading to the ban, are strictly regulated by the Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR).

The delicacy, prized by top-end restaurants around the world, fetches about $70 a kilogramme.

McCully says the Government will share "considerable evidence collected so far" with other countries, Interpol and CCAMLR.

"We will also work with INTERPOL to take action against those aboard the ship, encouraging other countries to take legal action against the company which purportedly owns the vessels, and most importantly working with the Spanish authorities to investigate the links between the vessels and the Spanish-based syndicate, Vidal Armadores SA," he added.

Asked how the two fishing boats, which appear rusty and in poor repair, managed to evade the offshore patrol boat, a defence spokesman said: "Ask MFAT [Ministry of Foreign Affairs and Trade]."

All questions to the navy on the operation have been referred to the foreign affairs ministry.

A spokeswoman for MFAT said: "It was an operational decision made for safety reasons."

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