The Government could explore the legal opportunity in the Maritime Crimes Act 1999, to release New Zealander Pete Bethune, the Green Party said today.

"Minister of Foreign Affairs Murray McCully has conceded jurisdiction in this case to Japan, but Japan's claim is arguably invalid. All the talk of the Government not being able to interfere with the Japanese legal system is a farce. The New Zealand legal system could be dealing with this issue," Green Party Oceans Spokesperson Gareth Hughes said.

New Zealand citizen Pete Bethune of the Sea Shepherd Conservation Society boarded the Japanese vessel Shonan Maru No 2 while in the high seas to make a citizen's arrest of the captain. The captain of the Shonan Maru No 2 allegedly rammed and destroyed the Ady Gil - a New Zealand registered vessel captained by a New Zealand citizen.

Australian based lawyer working in this field, Ronald Browne, has advised that New Zealand is a signatory to the Rome Convention for the Suppression of Unlawful Acts Against the Safety of Maritime Navigation.

This Convention was incorporated into New Zealand law through the Maritime Crimes Act 1999. Section 8 (1) of the Act specifies extra-territorial jurisdiction - that New Zealand law applies to acts committed against a ship in the high seas if that ship is registered in New Zealand.

Consequently, the captain of the Shonan Maru could be charged under New Zealand law for a crime punishable by up to 14 years in prison.

"I am surprised that the Government has so readily conceded jurisdiction, rather than exploring this legal opportunity," Mr Hughes said.

Mr Hughes said the crime was reported to the NZ Police by the Sea Shepherd Conservation Society, and the Police referred the case to the Maritime New Zealand. That was almost two months ago and there has been no word from NZ authorities.

"Mr Bethune did what our Government should have been doing which is standing up to illegal whaling. New Zealand needs to stand up for Mr Bethune and stand up for the whales," Mr Hughes said.

"Our Government's silence is disturbing. That it was silent on the ramming of the Ady Gil, and that it is silent on the plight of Pete Bethune illustrates a pervasive soft touch towards Japan's whaling industry. The Government is selling New Zealander's principles to the pro-whaling Japanese Government.

"John Key's Government must assert a claim of New Zealand jurisdiction in this case and bring Pete home. If John Key maintains a weak stance towards Tokyo, the only remaining option will be to take Mr Bethune's case to the International Court of Justice," Mr Hughes said.