The wife of a New Zealand anti-whaling activist being held on a Japanese whaling boat is repeating her call for government intervention.

Peter Bethune boarded the Shonan Maru No 2 in Antarctic waters in a bid to make a citizen's arrest in relation to the sinking of his own vessel, the Ady Gil, which was involved in a collision with the whaling ship. He wanted to charge the Japanese captain with the sinking and attempted murder of six activists. He also intended to present a bill for the boat.

However, he is now being held on board the Shonan Maru No 2 and is expected to be taken to Japan and charged with trespass. Bethune could face up to three years in a Japanese prison.

His wife, Sharyn, says it should not have got this far. She says the New Zealand Government has to step in because her husband was only trying to get justice for the deliberate ramming of the Ady Gil and the threat to its crew.

Mrs Bethune says her husband can stand up for himself but has not been in such a situation before.