Updated 1.39pm: Sea Shepherd activists are driving one of the two illegal fishing ships that were pursued by the Navy last month out of the Southern Ocean.

The Sam Simon has narrowly avoided collisions with both boats during separate pursuits in the last two days

Captain Sid Chakravarty says the boats have become aggressive when they've been contacted.

He says one of the boats came within five metres of the Sam Simon.

Sid Chakravarty says while they're pursuing one of the ships, they're both driving them away and preventing them from fishing.

"They can be pretty certain they would be better off just leaving these grounds and not resuming fishing."