GLAND, Switzerland (AFP) Illegal driftnets cast by Moroccan, French and Italian fishermen continue to kill thousands of dolphins in the Mediterranean each year despite an EU ban on the practice, the environmental group WWF warned Thursday.

An estimated 3,000 to 4,000 dolphins are caught annually in the Alboran Sea off the coast of Morocco, which comprises just three percent of the Mediterranean, according to a new WWF report that named a fleet of 177 Moroccan fishing vessels as the deadliest threat to marine life in the area.

A further 13,000 striped and short-beaked dolphins -- which were recently placed on a list of endangered species -- are ensnared around the Straits of Gibraltar and in neighboring zones, the conservation group said.

"The evidence we have gathered on the Moroccan fleet brings us to think that illegal driftnet fishing currently happening in the whole Mediterranean results in a massive slaughter of vulnerable species," said Paolo Guglielmi, head of the marine unit at the WWF Mediterranean program.

The report "Biodiversity impact of the Moroccan driftnet fleet in the Alboran Sea" also found that the boats captured about 23,000 sharks annually in the waters while another 77,500 were caught nearby. "More than 4,000 kilometres (2,500 miles) of illegal nets from the Moroccan, French, Turkish and Italian driftnet fleets are ensnaring all that gets in their way," Guglielmi said in a statement.

The slaughter is occurring despite a ban on driftnet fishing by the European Union since January 1, 2002 and a UN moratorium on large scale nets from 1992, and WWF urged the EU to implement its law.

Morocco is a non-EU country so it was not included in the EU ban, but companies from the 15-nation bloc supply Moroccan vessels with illegal driftnets, said WWF spokesman Olivier van Bogaert.

"It is illegal and that is what we are trying to denounce," he said.

About 75 French fishing boats and up to 100 Italian vessels still trawl the waters for swordfish, tuna and sea bream using the nets, claimed van Bogaert.

"They are not complying (with the law) ... the same goes for Spain but we don't have proof for this," he said.

WWF called on the European Union to monitor and prosecute all the fleets of its member states using driftnets.

And it urged the General Fisheries Commission for the Mediterranean and non-EU countries to introduce legislation banning these nets.

"The only valid way to prevent the massacre of dolphins, sharks and other marine species caused by these driftnet fleets in the Mediterranean is to make it a driftnet-free sea by enforcing a total ban on all the driftnet fisheries in the region," said Simon Cripps, WWF director of the endangered seas program.

The International Union for Conservation of Nature and Natural Resources (IUCN) added the Mediterranean short-beaked dolphin to its Red List of Threatened Species published earlier this week.

"Its population has declined more than 50 percent in the Mediterranean region over the last 30-40 years due to reduced dolphin prey in the Mediterranean because of overfishing and habitat degradation," the IUCN said.