Paul Watson, the “eco-pirate” who made headlines last year after freeing hundreds of bluefin tuna, risks losing the boat he used in his daring operation.

The flagship of his fleet, the Steve Irwin, named after the Australian conservationist and TV star, was impounded in Shetland after Watson’s crew allegedly damaged a fishing ship as they sprang 800 tuna from the nets off the Libyan coast.

Watson, a co-founder of Greenpeace and director of radical conservation group, Sea Shepherd, who is based in California, was about to leave Lerwick in the Shetland isles en route for the Faroes last week when the complaint was lodged against him in the Scottish courts.

The Steve Irwin was impounded by the court on 15 July and now the man described by the Japanese as a pirate has just days left to post a bond for £860,000.

Watson, 50, has managed to raise £305,000 in a Twitter campaign, but he has nine days left to stump up the remaining cash.

If he can’t, the Steve Irwin, named after the Australian conservationist, may have to be sold.

In a statement, Watson said that if the group fails to post the bond, "the Steve Irwin will be held indefinitely and possibly sold. This would not only be a financial hardship but more importantly, it could prevent us from reaching the Faroe Islands to protect pilot whales and threaten our ability to defend whales in the Southern Ocean Whale Sanctuary from the Japanese whaling fleet this December."

"Fish and Fish are claiming damages for the bluefin tuna we rescued from their nets in June 2010, fish that we believe were illegally caught after the season has closed, without an inspector onboard, or any paperwork documenting the legality of their catch".

Joseph Caruana, the claimant, denies the allegation.

He is reported to have said: “Sea ­Shepherd cannot continue behaving this way. I wanted to show that we mean business and will fight.”