Common dolphins, once a frequent sight in the Mediterranean, may soon be extinct in Greece's Ionian Sea due to overfishing, according to environmentalists.

WWF and a dozen other environmental organisations said research showed numbers of dark-grey, white-bellied dolphins had decreased from 150 to 15 in 10 years in protected areas in the Ionian, between Greece and Italy.

"It is called the common dolphin but the problem nowadays in the Mediterranean is that it's not common at all anymore. It is endangered. It is about to be extinct," WWF Greece-based expert Giorgos Paximadis said.

"Overfishing has caused the destruction of the marine environment and the dramatic decrease of common dolphins," said Dr Paximadis, adding that it deprived the dolphins of their food.

The environmental groups urged Greece to take measures, including the adoption of larger mesh size for all bottom-set nets, restrictions on trawling and on recreational fishing as well as stronger penalties for illegal fishing.

The common dolphin population in the Ionian Sea is one of the last in the Mediterranean, Dr Paximadis said. "As they are on the top of food web, it shows that the rest of the marine web is not healthy," he said.

Three other species of dolphins in Greece, including the bottlenose dolphin, are considered vulnerable but not yet in danger of extinction, he said.