DAKAR (Reuters) - West African countries have detained seven Chinese ships for fishing illegally and the boats’ owners could be subject to millions of dollars in fines, environmental group Greenpeace and government officials said.

Inspectors from Guinea, Sierra Leone and Guinea-Bissau boarded the ships off their coasts that they found to be violating regulations on catching protected fish and using nets with small holes to facilitate bigger hauls.

The arrests came after a two-month regional patrol on a Greenpeace ship, the Esperanza, that carried inspectors from the West African countries in a bid to supplement national efforts often hamstrung by budget and technology constraints.

“This is a surprisingly high amount of arrests, especially considering that the vessels knew about our patrols in advance,” Greenpeace’s Pavel Klinckhamers said on Tuesday.

West Africa has some of the richest waters in the world, but stocks are being depleted as industrial trawlers, some operating illegally, comb the oceans from the seabed to the surface, Greenpeace says.

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

The Esperanza patrol found 11 vessels in breach of regulations out of 37 stopped, and reported the breaches to local authorities, who towed them back to port.

Some of the ships were released after fines were paid. Others remain under investigation.

Two other foreign vessels were found to be non-compliant, including a European ship with shark fins aboard, and further investigations are under way, Greenpeace said.

Chinese Foreign Ministry spokesman Geng Shuang said China consistently opposes all forms of illegal fishing, and demands that firms operate legally and protect the maritime environment.

“China hopes that the relevant countries can enforce the law in a civilized manner, handle it in accordance with the law and protect the legal rights of the relevant Chinese companies and their employees,” Geng said.

An EU official in Dakar was not immediately available for comment. The EU, which imports around 874 million euros ($954 million) of fish products each year from West Africa, is subject to fishing quotas and pays compensation to local governments. It has also provided funding to crack down on illegal fishing.

Guinea’s fishing minister, Andre Loua, confirmed the detentions and added that it needed more money and boats to effectively control illegal fishing.

Sierra Leone Minister of Information Mohamed Bangura said three Chinese vessels had been detained and fines paid, without giving details. A Guinea-Bissau fishing official said fines were still being negotiated for some of the seized vessels.

(This version of the story has been refiled with Greenpeace correcting number of ships detained to 7)