Pete Bethune, captain of round-the-world trimaran Ady Gil, boarded the whaling ship from a Jet Ski

The skipper of sunken round-the-world trimaran Ady Gil, Pete Bethune, is being held “in custody” on a Japanese whaling vessel after climbing on board under the cover of darkness to attempt a citizen’s arrest on its captain.

Bethune boarded the Japanese vessel Shonan Maru No 2 in response to a collision in January with the Japanese whaling ship that left his boat, Ady Gil, missing a large section of hull. The boat, formerly known as Earthrace, later sank.

His plan was to attempt a citizen’s arrest on its skipper for the attempted murder of the six crew on board Ady Gil at the time of the collision and present him with an invoice of $3m for its replacement.

Agy Gil

The Japanese Institute of Cetacean Research, which operates the Japanese whaling fleets in the name of scientific study, released a statement this afternoon saying that Bethune had been restrained and was “in custody”.

This photo, top, released by the institute, shows where Bethune cut through the security netting on the side of the boat to gain access.

It is claimed that in the process he cut his hand, which has been treated by the Japanese crew. Bethune told the crew that he threw the knife he used into the sea after getting on board.

“The captain of the Shonan Maru No 2… gave notice today that in line with the Japanese Mariners Act he was taking necessary measures and restrained Mr Bethune,” the statement said.

“Mr Bethune is being held in custody on board the Shonan Maru No 2. Besides the protective net tearing there is no damage to the Japanese vessel nor are there any injuries to the crew.”