The Costa Rican government has officially confirmed its demand for the extradition from Germany of hardline conservation leader Paul Watson.
German authorities queried the status of an arrest warrant for Mr Watson, a Canadian, after he was detained at Frankfurt airport, Sea Shepherd spokesman Peter Hammarstedt said.
Costa Rica replied that he was wanted over an alleged navigation offence a decade ago, Mr Hammarstedt told Fairfax online.
"There is no other allegation against him," Mr Hammarstedt said, dismissing suggestions that Mr Watson faced claims of attempting to kill seamen aboard a Costa Rican fishing boat in 2002.
Mr Watson has been held in custody at Frankfurt airport since last Sunday, and in his most recent tweet said: "might have to stay one more night until we clear this up ... "
He is due to appear in a closed hearing again tonight, Australian time.
The case stems from a collision between Mr Watson's then ship, Farley Mowat, and the Costa Rican shark fishing boat Varadero in April 2002.
At the time, Sea Shepherd was campaigning in the central Pacific against shark finning.
After apprehending the Varadero in Guatemalan waters on what Sea Shepherd said were orders from Guatemalan authorities, Mr Watson was prosecuted when he went to Costa Rica.
Initial charges were dismissed, but with a renewed prosecution looming, Farley Mowat fled.
Mr Hammarstedt said an arrest warrant for Mr Watson had lapsed before it was reactivated last October.
This coincided with the commencement of a prosecution against Sea Shepherd by Japan's Institute of Cetacean Research in the US District Court in Seattle, he said.
Costa Rica has a recent record of voting against whaling in the International Whaling Commission.
Mr Hammarstedt said fishing interests from Japan, Taiwan and other countries maintained a strong presence in central American waters.
Costa Rican environmentalists say that, although shark finning is banned there, a trade in dried shark fins from other central American countries passes through its ports.
Interpol, the international co-operative policing agency, released a statement in which it said it refused in March to publish a Red Notice seeking Mr Watson's arrest because its Office of Legal Affairs was not satisfied the request complied with Interpol's constitution and rules.