Ric O'Barry, an anti-dolphin-hunt campaigner was detained in the town of Shingu in western Japan on Tuesday after being arrested the previous night for not carrying his passport.
He was 75-year-old star of “The Cove,” also Oscar-winner on documentary about Taiji's dolphin hunt in 2009.
Initially, police said they received an information that O'Barry might be drunk while driving. After he passed a breath test, he was then arrested after he was not with his passport.
Lisa Agabian, a spokesperson for Sea Shepherd, said by email that in previous years the group's activists have been followed and harassed by the police.
O'Barry was stopped and detained while going to his hotel from dinner at a restaurant, his son and his supporter activist Lincoln O'Barry said over the phone from Los Angeles.
In Japanese law, foreign visitors are to carry their passports or any official sort of ID.
O'Barry, an American, trained dolphins for the 1960s, known famously in "Flipper" TV series, but had a change of ambition and now campaigns against both capturing and killing the dolphins.