Updated on April 10, 2014 at 9:45 a.m. EDT.

Part of our special eight month series "The Future of Food".

Do you know if the fish on your plate is legal? A new study estimates that 20 to 32 percent of wild-caught seafood imported into the U.S. comes from illegal or "pirate" fishing. That's a problem, scientists say, because it erodes the ability of governments to limit overfishing and the ability of consumers to know where their food comes from.

The estimated illegal catch is valued at $1.3 billion to $2.1 billion annually and represents between 15 and 26 percent of the total value of wild-caught seafood imported into the U.S., report scientists in a new study in the journal Marine Policy.

Study co-author Tony Pitcher says those results surprised his team. "We didn't think it would be as big as that. To think that one in three fish you eat in the U.S. could be illegal, that's a bit scary," says Pitcher, who is a professor at the fisheries center of the University of British Columbia in Vancouver.

To get those numbers, Pitcher and three other scientists analyzed data on seafood imported into the U.S. in 2011. They combed through government and academic reports, conducted fieldwork, and interviewed stakeholders.

The scientists report that tuna from Thailand had the highest volume of illegal products, 32,000 to 50,000 metric tons, representing 25 to 40 percent of tuna imports from that country. That was followed by pollack from China, salmon from China, and tuna from the Philippines, Vietnam, and Indonesia. Other high volumes were seen with octopus from India, snappers from Indonesia, crabs from Indonesia, and shrimp from Mexico, Indonesia, and Ecuador.

Imports from Canada all had levels of illegal catches below 10 percent. So did imports of clams from Vietnam and toothfish from Chile.

View Images NG STAFF. SOURCE: P. GANAPATHIRAJU, ET AL., MARINE POLICY

In response to the study, Connie Barclay, a spokesperson for the National Oceanic and Atmospheric Association (NOAA) Fisheries, said, "We agree that [pirate] fishing is a global problem, but we do not agree with the statistics that are being highlighted in the report." Barclay says data are too scarce to make the conclusions verifiable.

But, she adds, "NOAA is working to stop [pirate] fishing and the import of these products into the U.S. market." She points to recent increased collaboration with other law enforcement agencies and improved electronic tracking of trade data.

Pirate Fishing

The U.S. is important to consider when it comes to fishing because it is tied with Japan as the largest single importer of seafood, with each nation responsible for about 13 to 14 percent of the global total, says Pitcher. Americans spent $85.9 billion on seafood in 2011, with about $57.7 billion of that spent at restaurants, $27.6 billion at retail, and $625 million on industrial fish products.

However, what few Americans realize, says Pitcher, is that roughly 90 percent of all seafood consumed in the United States is imported, and about half of that is wild caught, according to NOAA.

Pirate fishing is fishing that is unreported to authorities or done in ways that circumvent fishery quotas and laws. In their paper, the authors write that pirate fishing "distorts competition, harms honest fishermen, weakens coastal communities, promotes tax evasion, and is frequently associated with transnational crime such as narcotraffic and slavery at sea." (See: "West Africans Fight Pirate Fishing With Cell Phones.")

Scientists estimate that between 13 and 31 percent of all seafood catches around the world are illegal, worth $10 billion to $23.5 billion per year. That illegal activity puts additional stress on the world's fish stocks, 85 percent of which are already fished to their biological limit or beyond, says Tony Long, the U.K.-based director of the Pew Charitable Trust's Ending Illegal Fishing Project.

"The ocean is vast, so it is very difficult for countries to control what goes on out there," says Long. He explains that pirate fishers are often crafty, going to remote areas where enforcement is lax. They may leave a port with a certain name on the boat and the flag of a particular country, engage in illegal fishing, then switch the name and flag and unload their catch at a different port.

In Marine Policy, the authors wrote that their paper "does not suggest that importers, distributors, retailers, or consumers of fish in the USA or elsewhere are aware of this situation." They added, "Seafood supply chains are notoriously opaque such that consumers and vendors of fish are generally unaware of the role they play in buying and selling illegally caught products."

The Grocery Manufacturers Association declined to comment for this article. Gavin Gibbons, a spokesperson for the National Fisheries Institute, the leading trade group for the U.S. seafood industry, says his organization has taken action to crackdown on pirate fishing and calls the new study "fundamentally flawed."

Gibbons says the report relies too much on anecdotal evidence and fails to recognize price signals. On the former point, the study overestimates the amount of salmon from China that had Russian origins, and on the latter, the study fails to explain why some fish would get labelled as less valuable product, such as from higher-priced Atlantic cod to lower-priced haddock, he says.

But Pitcher says the biggest source of illegal imports is processing plants in China, which handle the majority of seafood consumed in the U.S. "In many cases there is no documentation there, so illegally caught stuff can be deliberately or inadvertently mixed in," says Pitcher.

View Images These Chinese boats were captured by the South Korean coast guard for alleged illegal fishing in South Korean waters in November 2011. PHOTOGRAPH BY DONG-A ILBO, APF/GETTY

Doing Things Differently

David Pilat, the global seafood buyer for Whole Foods Market, says his company combats pirate fishing in a number of ways. The store chain buys products that are certified by the independent Marine Stewardship Council, which has strict chain-of-custody requirements that prohibit illegal fishing. Whole Foods also sends buyers directly to docks to pick up fish when it is brought in, before it gets into a system of distributors and processors.

Finally, Whole Foods uses a software program called Trace Register that tracks seafood at every step of the supply chain. "We want our customers to know exactly where their seafood comes from, and to feel confident they're getting exactly what they paid for," says Pilat. (See: "Entrepreneurs Fight for the Future of Fish—Beginning With the Bottom Line.")

Other U.S. companies have started adopting similar measures in recent years, including Costco, Trader Joe's, Darden (owner of Red Lobster, Olive Garden, and other chain restaurants), and many independent restaurants.

Such verifiable supply chain documentation is a great way to combat illegal fishing, says Pramod Ganapathiraju, a co-author of the Marine Policy study who is also at the University of British Columbia.

Ganapathiraju says the U.S. government should also take a more active role in preventing imports of illegal seafood. More resources should be dedicated to port inspections and verification of documentation, he says. (See: "Can Technology End Pirate Fishing?")

Long adds that he would like to see universal tracking numbers for all commercial fishing vessels so that crews can't get away with changing boat names or flags to evade detection.

When it comes to the processing industry in China, Pitcher says companies there already spend a considerable amount of money and effort on making sure products meet health and safety standards. "So if demand for documentation was as rigorous, I don't think the industry would find that too difficult or expensive," he says.

View Images Whole Foods Market takes several steps to combat pirate fishing, including using a software program that tracks seafood at every step of the supply chain. PHOTOGRAPH BY RICK BOWMER, AP

Government Action

The U.S. government made a strong step forward on April 3, says Long, when the Senate ratified the international Port State Measures Agreement, which would empower port officials to prohibit foreign vessels that are suspected of illegal fishing from receiving port services and access. That would hit pirate fishers in their pocketbooks, says Long.

The treaty was adopted by the United Nations in 2009 and will go into effect when 25 countries ratify it. The U.S. was the 11th party to do so.

The U.S. government should also pass the proposed Safety and Fraud Enforcement for Seafood Act, says Ganapathiraju. That would require traceability throughout the seafood supply chain, improve inspections, and provide more information to consumers at the point of purchase.

The U.S. could also take a tougher stance on nations that fail to curtail pirate fishing, says Long. The European Union recently banned seafood imports from Belize, Cambodia, and Guinea as a result of those nations' fishery policies, he notes. (See: "Passenger Ship Spots Illegal Activity.")

"The federal government can and must use its existing authority to shut our borders to illegally caught seafood and level the playing field for honest fishermen and seafood businesses," says Beckie Zisser of Oceana, who supports passage of the proposed safety and fraud act.

In the meantime, companies and consumers can "ask the right questions" about the source of their seafood, says Long. If suppliers can prove that their fish was caught legally, it raises the value of their product, he says.