Australia and France will step up patrols for illegal fishing in the Southern Ocean under a new agreement signed by the two countries.

The Federal Government says the agreement includes cooperation in apprehending, seizing and investigating fishing vessels that are believed to have broken the law.

The patagonian tooth fish is among the species under threat.

French patrols will also include Australian fisheries officers, and Australian vessels will carry French officers so that each country is able to apply the laws of the other to offenders.

The area covered by the agreement stretches from Heard Island to the French territories of Saint-Paul and Amsterdam islands.