Foreign fishing vessels, many from China, prowl the waters off West Africa every day. They capture millions of fish — catches that used to go to local boats. The fish are then shipped to China, Europe and the United States, satisfying a global demand for seafood and fueling a multibillion-dollar industry.

The foreign vessels make life hard for West African fishermen.

Foreign trawlers from Asia and Europe have cost West Africa's economy 300,000 jobs and $2 billion in income, according to John Hocevar, a marine biologist with Greenpeace.

However, what to do about the problem — and possible damage to regional fish populations — has eluded experts and officials.

Overfishing in West African waters has depleted st FILE - Overfishing in West African waters has depleted stocks of high-quality fish in Senegal, May 29, 2017. (R. Shryock/VOA) FILE - Overfishing in West African waters has depleted stocks of high-quality fish in Senegal, May 29, 2017. (R. Shryock/VOA)

Chinese presence

Exact numbers are difficult to come by, but experts agree no single country has a greater presence off the coast of West Africa than China.

In a 2015 report, Greenpeace estimated that, two years earlier, China had 426 distant water fishing vessels off Africa's West Coast.

Between 2000 and 2011, 64 percent of China's average annual catches, valued at more than $7 billion, came from that area, according to The Pew Charitable Trusts.

Fishing isn't a big part of China's economy, representing less than one percent of total gross domestic product. But for many in China's coastal provinces, it's both a livelihood and way of life, according to Haibing Ma, the China program manager for the Worldwatch Institute, a nonprofit group that researches sustainability.

Chinese fishers have traveled to Africa because their own fish stock has nearly run out. "Overfishing has destroyed the sustainability of China's inshore fisheries," Ma said.

Greenpeace reveal new cases of bad fishing practic FILE - After witnessing several irregularities involving local and foreign fishing vessels in West Africa, Greenpeace called for a regional fisheries management body in the region. FILE - After witnessing several irregularities involving local and foreign fishing vessels in West Africa, Greenpeace called for a regional fisheries management body in the region.

Lack of oversight

Fishing practices are inherently difficult to monitor and regulate. Oceans are vast, vessels are hard to reach, and a mix of local and international laws and regulations complicates enforcement.

Domestic laws regulate waters up to 200 miles off the coast, and international laws control waters past that, according to Todd Dubois, assistant director of the National Oceanic and Atmospheric Administration Fisheries Office for Law Enforcement.

This complex environment has led to a variety of creative ways to maximize profits without breaking the law.

For example, legislation in Guinea-Bissau has kept large industrial fishing vessels away from its coast. So, fishing companies have deployed small boats that don't need licenses from nearby countries such as Senegal. Those boats will fish in Guinea-Bissau and return their catches to a large "mothership," which in turn takes its bounty back to Senegal to be traded.

In other cases, "floating factories" — large, nearby vessels used for processing and packaging catches — have enabled other boats to catch small pelagics, such as mackerels and sardines, quickly and on a massive scale for prolonged periods.

And bottom trawls, a kind of gear that contributes to overfishing, were installed on most Chinese vessels studied by Greenpeace in 2015.

Many see international fishing off Africa's West Coast as an exploitation of local resources by foreign powers. But some of the most damaging practices occur within the law, and local African economies sometimes benefit from illegal fishing.

In Mauritania, for example, a Chinese company made a secret deal with the local government to build a fish-processing factory and bring 80 large vessels to the coast in exchange for a $100 million investment in the country.

That deal may have benefited both countries, says Andre Standing, an adviser at the Coalition for Fair Fisheries Arrangements, but it has had a profoundly negative impact on small-scale fishermen.

FILE - Chinese fishing trawlers anchor off the coa FILE - Chinese fishing trawlers anchor off the coast of Freetown, Sierra Leone, Nov. 18, 2012. FILE - Chinese fishing trawlers anchor off the coast of Freetown, Sierra Leone, Nov. 18, 2012.

Responsible practices

Fishing, even when done on a massive scale, can be sustainable, provided there's adequate planning and reporting. That means understanding the vulnerability of local fish populations and managing catches accordingly.

"Some reproduce very fast and can handle quite heavy fishing, such as tuna, and some of the small pelagics like the sardines," Standing said, but other fish, such as sharks, develop very slowly. "We're already seeing across Africa and across the world that industrial fishing and long line fishing in particular, they've decimated populations of the other types of fish."

Standing cautions against drawing conclusions about the entire Chinese fishing industry. Individual fishing companies need to be judged on their own merits, he said. There are good Chinese companies, just as there are bad European companies.

China's presence off Africa's west coast shows no signs of shrinking, though. The Chinese government has enabled the industry to expand far beyond the country's own shores. In 2013, the government gave the fishing sector about $6.5 billion in subsidies, according to a brief Standing wrote for the Africa Center for Strategic Studies.

Whether considering the actions of China, the European Union, or local African governments and businesses, the root of the problem comes from a lack of focus on long-term sustainability, according to Standing.

"In many areas, there really isn't this careful, precautionary approach to managing fishing intensity," he said. "A lot are being driven by short-term profit, and that's really at the heart of the unsustainable nature of fisheries."