A German court on Monday ordered Paul Watson, the founder of marine conservation group Sea Shepherd, to remain in custody a day after his arrest on a warrant from Costa Rica.
The veteran anti-whaling campaigner, a Canadian national, was detained in Frankfurt on Sunday on charges stemming from a high seas confrontation over shark finning in 2002.
He is accused of having "put a ship's crew in danger" in the incident, a Frankfurt prosecutor said.
Watson's lawyer Oliver Wallasch said that after Monday's court hearing that his client must remain in custody until the Costa Rican extradition request is considered, adding that he did not know how long the process would take.
"My client is shocked," Wallasch said.
A media report in Australia, citing Costa Rican reports, said Watson, 61, also faced an outstanding warrant for attempted murder during the same incident.
"The German police have said that the warrant for Captain Watson's arrest is in response to an alleged violation of ships traffic in Costa Rica, which occurred during the filming of 'Sharkwater' in 2002," Sea Shepherd said.
The specific "violation of ships traffic" incident took place in Guatemalan waters when Sea Shepherd encountered an illegal shark finning operation, run by a Costa Rican ship called the Varadero, it added in a statement.
"On order of the Guatemalan authorities, Sea Shepherd instructed the crew of the Varadero to cease their shark finning activities and head back to port to be prosecuted," the group said.
It claimed that while escorting the Varadero back to port, the tables were turned and a Guatemalan gunboat was dispatched to intercept the Sea Shepherd crew.
"The crew of the Varadero accused the Sea Shepherds of trying to kill them, while the video evidence proves this to be a fallacy," said the group, which was set up in 1977 to campaign against the slaughter of ocean wildlife.
"To avoid the Guatemalan gunboat, Sea Shepherd then set sail for Costa Rica, where they uncovered even more illegal shark finning activities in the form of dried shark fins by the thousands on the roofs of industrial buildings."
The 61-year-old Watson was passing through Frankfurt on his way to France to attend conferences when he was arrested, said a member of Sea Shepherd's German branch Olav Jost who was with Watson during the first hours of his detention.
"He was extremely surprised at being stopped since he has visited Germany and elsewhere in Europe in the past without any problems," Jost said.
Watson was being assisted while in custody by European Parliament members Daniel Cohn-Bendit and Jose Bove, Sea Shepherd said.
"Our hope is that these two honourable gentlemen can set Captain Watson free before this nonsense goes any further," the group said.
Cohn-Bendit told AFP that "I am going to try to intervene with the German government to try and resolve the situation."
Sea Shepherd is best known for its annual pursuit of the Japanese whaling fleet in Antarctica, using increasingly militant ways to halt the hunt.
This year, after setting off from Australia, the group hurled stink bombs at the boats on the high seas and used ropes to try to tangle their propellers in a series of exchanges which saw the whalers retaliate with water cannon.
The whaling fleet killed less than a third of the animals it planned to because of the sabotage attempts.
Watson, whom Sea Shepherd members affectionately call "the captain" and who looks the part with a thick shock of white hair and beard, has said that his organisation was the only navy in the world that defends the oceans.
"Our goal is to protect the oceans because if they die, we will all die," he told AFP in a 2010 interview.