Environmentalists and tuna fishers manoeuvering at sea

Environmentalists on the Mediterranean sent a small launch this morning to inspect a sea cage to determine whether it was holding tuna, but fishermen attacked them with debris, forcing a return to the mother ship.

Three Tunisian fishing boats circled the cage to protect it — and, presumably, the fish inside. They also deployed two small dinghies of their own to chase the launch sent by the environmental group, the US-based Sea Shepherd Conservation Society.

The environmentalists returned without being able to inspect the cage. Those in the boat said the Tunisians threw large metal rings at them, but none landed in the launch.

Bluefin tuna are a prized delicacy in top Tokyo restaurants, where a thin slice prepared as sushi can fetch 2,000 yen (£15). Most of the catch is flash frozen and flown to auction at the Japanese capital's vast Tsukiji market. One large specimen fetched a record 32.49 million yen, nearly £250,000, in January.

Sea Shepherd, which has no official enforcement powers, is trying to disrupt illegal fishing for bluefin tuna. The stock of the fish is dwindling to the point where experts fear its collapse.

The Tunisians radioed the French military today to say the Sea Shepherd divers were in the water trying to attack their net. That was not the case. But a French fighter jet soon appeared and flew extremely low over the Tunisian boats and the Steve Irwin, the Sea Shepherd ship.

A spokesman for the environmentalists said two of the Tunisian boats are not allowed to fish legally, according to a list prepared by ICCAT, the International Commission for the Conservation of Atlantic Tunas. But it was not clear if the other boats in the area are permitted.

Divers on the Steve Irwin are standing by, prepared — if they can — to go into the water and cut the net to free any tuna caught illegally.

In this case, the group did not deploy divers, as it did not appear safe due to the aggressive actions of the Tunisian fishermen.