New Zealand marine activist Pete Bethune's case against the Sea Shepherd and its founder Paul Watson begins in court today in the US.

Mr Bethune took a case to force Sea Shepherd to pay US$500,000 (NZ$616,600) he says he is owed for the initial purchase of his boat, the Ady Gil.

The boat was rammed by a Japanese whalers while taking part in a Sea Shepherd campaign in the South Ocean whale sanctuary in 2010.

Paul Watson will be a witness in court despite him having just skipped bail from Germany where he was being held following an extradition order issued by the Costa Rican authorities.


"I am extremely sad that I have been forced to bring this case to court against an organisation that I loved and a man that I had great respect for," said Bethune in a statement before the case.

"I sacrificed a year of my life to Paul and the Sea Shepherd, including five months locked up in a maximum security prison in Japan resulting from actions I took under the captaincy of Paul."

Mr Bethune was expelled from the Sea Shepherd while he was in jail in Japan.

He said its treatment of him publicly and privately since his time in jail had been a disgrace.

"The Japanese at least treated me with dignity and respect," he said.

"Sea Shepherd in contrast has treated me like a used condom, throwing me away once I'd served its purpose," said Mr Bethune.

"Not only has the court case taken up a lot of my time, but the financial difficulties I have faced because of the money Sea Shepherd owes to me have also been a huge concern."

"At least in court, the case will be decided based on merit, rather than lies and half truths. I am looking forward to seeing an end to it all and being able to concentrate on the mountainous challenges to our marine environment rather than my mountainous debts."

Mr Bethune has set up his own marine conservation organisation called Earthrace Conservation.

He next plans to tackle illegal fishing off the coast of Africa.

The case begins arbitration today in Annapolis, Maryland.