Earlier this year, whale hunters and environmentalists clashed in the Southern Ocean.

A high-speed environmentalist vessel, the Ady Gil, and a Japanese security vessel collided, in a culmination of weeks of tension over whale hunting.

After the incident, the captain of the damaged trimaran, Pete Bethune, boarded the Japanese ship, Shonan Maru 2, to deliver a letter of protest.

He was then held on board the vessel for just under a month, taken back to Tokyo and arrested by Japanese authorities on Friday morning.

The New Zealander is expected to be charged with trespass.

[Tatsuro Shinjo, Japan’s Coast Guard Sub Chief]:
"Well, he readily nodded in agreement when we presented him with the charges, but it's hard to say that he truly agreed, as we need to ask him properly and get a verbal answer. But that in general is how he acquiesced to be escorted to the police station."

Crowds of media awaited his arrival on the pier, along with a handful of pro-whaling demonstrators who voiced their demands.

[Shuhei Nishimura, Whaling Supporter]:
"We want the Japanese government to punish the activist as severely as possible under Japanese law and ask the New Zealand government to take away the Ady Gil vessel's ship registry."

Sea Shepherd's attempts to block the annual whale hunt have sparked irritation in Japan, where the government says whaling is an important cultural tradition.

Commercial whaling was banned under a 1986 moratorium, but Japan still hunts for what it says are research purposes.