South African fisheries inspectors hurled thunderflashes at a fleeing vessel fishing illegally with gill nets off Mozambique before boarding it by ramming their inflatable boat into the vessel's stern and grabbing hold of the handrail.

This is the second illegal fishing vessel to be arrested this month in a joint operation by South African and Mozambique fisheries authorities operating from Marine and Coastal Management's patrol vessel Eagle Star.

The Chinese vessel, Nong Jyl Lih, was using illegal industrial gill nets, called "walls of death" because of the underwater destruction they cause, and had between 20 and 30 tons of giant guitarfish on board

Giant guitarfish are listed as a "vulnerable" species by the World Conservation Union and have been targeted intensively for their fins, regarded as a delicacy in Asia.

The Eagle Star was patrolling Mozambican waters at the request of the Mozambique government, with fisheries staff from both countries on board, when they arrested the vessel on March 11 about 80 nautical miles from Beira.

Marcel Kroese of Marine and Coastal Management said in a telephone interview from the Eagle Star yesterday that the patrol vessel had investigated all fishing boats they had come across.

Kroese said: "The Nong Jyl Lih fled as soon as we came within a mile of it. They cut their nets and steamed off and ignored all our calls on the radio to stop. They were going at full speed.

"We had a rubber duck which we launched from the Eagle Star with a team on board. The guys rammed the rubber duck up the stern of the vessel so one of them could grab the railing and climb on board. The others threw a rope over and he pulled a rope ladder up and the rest boarded.

"I don't think the crew even knew they were on board, because when they didn't stop we had thrown a few thunderflashes at the vessel and the crew had run below.

"The Mozambicans then ordered the captain to stop for an inspection." Kroese said they found tons of frozen fins of several other shark species in the hold, while the giant guitarfish were frozen whole. The Chinese vessel had a licence to fish in Mozambican waters, but not to use a gill net.

The vessel was taken to Beira where the Mozambicans are preparing charges.

Giant guitarfish fins are among the most valuable of any species and the fish has been heavily targeted, particularly by Indonesian fishermen. This species occurs in the Western Indian Ocean from the Red Sea to South Africa.

There have been substantial declines in catches of giant guitarfish and there is virtually no effective management of the species.

Shark expert Len Compagno, of the Iziko Museum, said some guitarfish species in South America were critically endangered.

"Guitarfish are very vulnerable because they occur almost exclusively in inshore waters less than 100 metres deep and so are easily accessible," Compagno said.

"This practice is going to continue and it's a big problem." On March 10, the Eagle Star arrested an Indonesian vessel, the Shin Iu Peng, in Mozambican waters. It was also fishing with banned gill nets.