The Australian crew of the Sea Shepherd have come to the rescue of an illegal fishing vessel sinking off the coast of West Africa.

The Melbourne-based crew of the Bob Barker responded to a distress signal from the pirate fishing vessel the Thunder, the very ship they had been chasing for the past 110 days.

The sinking ship Credit:Simon Ager

Speaking on a satellite phone from the deck of the Bob Barker, Captain Peter Hammarstedt said he received the mayday signal about 6am local time on Monday and immediately responded to the call.

"We sent out our own crew to assist straight away. It was clear the ship was sinking," Captain Hemmarstedt said.