Conservation group Sea Shepherd suspects crew from a poaching vessel may have deliberately scuttled their ship off the west coast of Africa.
It says its vessel Bob Barker received a distress call from the Thunder yesterday that it was sinking. The group claims the Thunder had been poaching toothfish, and had been pursuing it for 110 days, since it was flagged by Interpol as a ship that was operating illegally.
All 40 crew members were rescued by the Bob Barker and another Sea Shepherd vessel, the Sam Simon.
Bob Barker captain Peter Hammarstedt suspected that as a final act, the Thunder's crew sank their boat.
When the ship went down the captain of the vessel was seen cheering and applauding from a lifeboat, said Mr Hammarstedt.
"I would not be surprised that the captain of this vessel, knowing that his ship is going to be arrested coming into port, would consider sinking his ship in order to destroy the evidence."
Mr Hammarstedt said the fishing vessel sank to a depth of 3800 metres, which wold destroy all evidence of poaching. He said the Bob Barker's chief engineer inspected ship before it sank, and all hatches were left open, pointing to the sinking as incredibly suspicious.
The crew of the Thunder will be handed over to authorities in Sao Tome.