Anti-whaling activist Pete Bethune arrived home to lash out at the organisation claiming to have secretly supported him through his ordeal.

Bethune, at his Torbay home yesterday, said he was angry and had been given only "half the story" by Sea Shepherd International.

The organisation claimed to have dumped him - then came out after sentencing to say it was a ploy to help win a lighter sentence.

It emerged yesterday that Bethune and his family were never told the dumping was a ploy.

He said: "There's some things I'm heavily upset about. But I've only got half the story at the moment, and that's my half. I feel like I'm in a black hole ... an information vacuum."

Bethune's anger came following five months in a Japanese jail after he boarded Japanese whaling ship Shona Maru II and attempted a citizen's arrest.

The charges included obstructing commercial activities, trespass, vandalism and carrying a knife. On Wednesday he was sentenced to two years in prison - suspended for five years - and released to return to New Zealand.

Bethune's anger came as Sea Shepherd International president Lawrence De Goot flew into New Zealand to meet with Bethune. He admitted last night keeping Bethine and his family in the dark to make the "dumping" look real.

"We needed a genuine reaction from his family. There's no need for him to be angry. We had to do it that way."

Sea Shepherd New Zealand boss Bill Watson accused the international arm of a "serious ethical breach" over the deception.

"It was unfortunate the way it was handled. Pete and his family and the New Zealand Sea Shepherd were not told of what they were doing when they disowned him. As far as I'm concerned that was a serious ethical breach."

Bethine said he had gone through a terrible time during his five months in prison.

"I'm a different person already. You don't do a lag like that without it marking you. Spending all that time with killers and drug addicts who are having to go cold turkey, it's affected me.

"The worst thing is having no idea when you're going to get out, and the solitary confinement. It's going to take me some time to process what I've been through."

He enjoyed an upgrade for his flight home on Air New Zealand. "I had a coke, which was my first bit of caffeine in five months. Then I had eye fillet ... every time the steward went past with food I'd have more."