DAKAR (Reuters) - Senegalese authorities have detained seven Chinese trawling vessels for illegally fishing in its waters, the country’s navy said on Saturday.

A Senegalese patrol boat intercepted the vessels off the coast of Senegal’s southern Casamance region on Friday, naval Captain Karim Mara, head of the patrol mission, told Reuters by telephone.

“The trawlers were caught in the flagrant offence of fishing without authorisation in Senegalese waters,” Mara said.

West Africa has some the richest fish stocks in the world, but they are being rapidly depleted by industrial trawlers, some operating illegally.

A study in the journal Frontiers in Marine Science estimates West Africa’s annual losses from illegal and unregulated fishing at $2.3 billion.

Chinese fishermen, as well as employees from Guinea-Bissau and Guinea were aboard the boat, Mara said.

Last month environmental group Greenpeace said West African countries have detained eight Chinese ships for fishing illegally and that the boats’ owners could be subject to millions of dollars in fines.