(CNN) -- "Pirate" fishermen are roaming the seas along West Africa and looting marine treasure from some of the world's poorest countries.
According to the Environmental Justice Foundation (EJF) these illegal, unregulated fisherman are taking an estimated $1 billion worth of fish from African waters each year.
For countries along the west coast, such as Sierra Leone, still recovering from over a decade of civil war, fishing is a vital source of employment and food.
"The trawlers have taken all the fish from the sea," local fisherman Senesie Kamara told the EJF. "There are so many patrolling we cannot fish. They destroy everything.
"The trawlers are destroying our only means of survival," he added. "The land is no good for farming. Fishing is what we know -- it is part of us."
Domitilla Senni, consultant to the Pew Environment Group, says countries like Sierra Leone are an easy target.
"Illegal, Unreported and Unregulated (IUU) fishing is a global problem as it affects most of the world fishing areas, but regions with weak governance structures, poor management and controls may suffer more from IUU fishing activities," she explained.
The EJF says the number of foreign pirate fishing vessels has multiplied in recent years taking advantage of the Sierra Leone government's lack of capacity to monitor and control its waters.
The pirate fishing vessels most recently documented by the EJF are operated by companies based in Las Palmas and Spain on behalf of owners based in South Korea.
Andy Hickman, Oceans Campaigner for the EJF, says the demand for seafood in the EU and Far East makes it a bustling business.
"There is a very high likelihood that consumers have bought and eaten fish that has been caught illegally," he said. "The EU Fisheries Commissioner estimated that as recently as 2009, up to 16% of EU imports were coming from illegal sources."
Hickman says it's hard for consumers to know if they are eating stolen fish because the traceability standard for seafood is often very weak.
The EJF operates a surveillance vessel that responds to callouts from local communities when pirate fishermen are spotted in their waters.
Amara Kalone is in charge of running the boat and acts as a crucial link to the local fishing community. He gathers information and evidence of pirate activity that helps to build a case against them. When it's possible, the criminals are prosecuted under national and international law.
"EJF is not authorized to make arrests of illegal fishing vessels," he explained. "But by documenting and taking photographs with GPS positions we can forward it to the European Union, Ministry of Fisheries and Marine Resources and the Sierra Leone Navy for action."
Kalone says local fishermen tell him they're catching a lot less than they used to because the rogue operators are working in the Inshore Exclusion Zone (IEZ). This is an area that's supposed to be reserved for local fishermen and women.
"The artisanal fishermen set their bottom set nets or long lines and hooks in the IEZ and are cleared away by these trawlers, leaving them in absolute poverty," he continued.
Confronting the pirates is risky business for the fishermen. Kalone says that local fishermen have been injured or killed trying to protect their fishing gear from industrial trawlers
The risk of getting caught is slim. The boat operators cover up the vessel names and markings that make them identifiable. Many also fly a "flag of convenience," something the EJF is campaigning against.
A ship is said to fly a "flag of convenience" if it flies a flag other than that of its country of ownership. The EJF says some nations sell their flags to foreign-owned fishing vessels, but lack the capacity or will to regulate and patrol their activities.
Greenpeace says flags can be bought over the internet for as little as $500 from countries such as Malta, Panama, Belize, and Honduras.
Hickman also adds that the boats are able to operate thousands of miles from the authorities by rarely docking into a port.
"These vessels are able to avoid coming into port by refueling and resupplying at sea, and by transhipping their catch to larger refrigerated cargo vessels," he said.
Only fish that is deemed valuable on the international market is kept and the crew throw away the rest. The EJF says that up to 90% of fish caught is simply dumped back into the sea dead.
As well as community surveillance the EJF is also campaigning for a global record of fishing vessels. It says it would be easier to identify illegal vessels if there was information available about each country's fleet, such as where the boats are operating and who owns them.
Senni says that in 2009 the EU approved a new set of rules on IUU fishing making it harder for illegal catches from places like West Africa to make it onto the market.
But she agrees there needs to be a global response to really combat the problem.
"What is needed are international agreements that can set clear rules such as transparency of ownership, operations and catches, full traceability of products and heavy sanctions for states not fulfilling their obligations," she said.