Anti-whaling activist Pete Bethune says he fully supports the Sea Shepherd Conservation Society, despite the organisation "booting him out" during his trial in Japan.

Mr Bethune was banned from the Sea Shepherd for having a bow and arrows on board his boat the Ady Gil when it collided with the Japanese Shonan Maru 2 and sank in Antarctic waters.

He told media today that he had felt betrayed by the organisation when he heard the news from a journalist while inside a Japanese prison.

The 45 year-old described it as a low point during his four months behind bars while he waited for sentencing.

Mr Bethune was sentenced to two years' jail, suspended for five years, for assaulting a whaler by hurling a rancid butter stink bomb during a high-seas confrontation, carrying a knife and disrupting commercial activities.

He returned to Auckland on Saturday and told media he had been in an "information vacuum" about the Sea Shepherd's reasons behind the ban.

Today he told journalists he was fully committed to the organisation and believed the Sea Shepherd's explanation that the ban was only a ploy.

"I think it could have been handled better. I still don't understand the Japanese legal system, so I don't know if it helped my case or not," Mr Bethune said.

He put the communication problems down to the organisation's growth over the last year.

Mr Bethune said he has seen an email from Sea Shepherd leader Paul Watson which he said proved that the ban was only a ploy.

"I firmly believe what the Sea Shepherd stands for and I will always be opposed to Japanese whaling," Mr Bethune said.

He said he did not know if he would be back in Antarctica for the next whaling season and wanted to spend time with his daughters Alycia and Danielle.

Former Ady Gil crew member and Sea Shepherd spokesman Laurens De Groot said Mr Bethune was a hero and was welcome to take part in future protests.

He said few people were told of the real reasons behind banning Mr Bethune, in order for the reaction to be "genuine".

"We knew he was never going to have a fair trial there, it was a political trial. In order for us to convince the judges, we knew we had to take a drastic measure," Mr Der Groot said.

He said he thought the ploy had worked.

Mr De Groot said Mr Bethune's lawyers had been informed of the ploy but the word had not got through to Mr Bethune and that was unfortunate.

Asked if the ploy may have damaged the integrity of the organisation amongst supporters, Mr De Groot said people donate to help the organisation protest in the Antarctica.

"They can still trust us," Mr De Groot said.