Mariners of old believed that an albatross following their ship signified good luck, but fishermen illegally trawling the Indian Ocean now have cause to be wary of the majestic seabirds.

Some 250 albatrosses are being equipped with tiny transceivers that will automatically pick up trawlers’ radar signals.

Their locations will be transmitted to the French navy, which will use the data to identify vessels fishing in prohibited waters in the Indian Ocean, off the remote French islands of Crozet, Kerguelen and Amsterdam. France is responsible for patrolling some 260,000 square miles of the southern sea.

Vessels fishing illegally generally switch off their automatic identification system (AIS) to avoid being tracked by satellite, but they cannot navigate safely without emitting low-level radar signals which the birds’ transceivers can detect as they fly over the ships.

Sailing without radar in the rough waters of the Indian Ocean would be extremely reckless. “Radars mean safety, especially for illegal ships that have to detect and avoid naval vessels,” said Henri Weimerskirch of the Chizé Biological Research Centre in western France. “Half of the boats we detected [during trials] did not have their AIS switched on.”