Stopping illegal fishing requires a combination of satellite surveillance, DNA-based seafood testing, international policy agreements, and closing the regulatory loopholes that let bad actors hide. Illegal, unreported, and unregulated (IUU) fishing costs the global economy an estimated $10 to $23.5 billion annually, with illegal and unreported catches making up 13 to 31% of the world’s total fish harvest. The problem spans from small artisanal boats operating without permits to massive industrial fleets exploiting weak oversight on the open ocean.
Why Illegal Fishing Is So Hard to Police
The ocean is enormous, and most of it falls outside any single country’s jurisdiction. Industrial fishing vessels can stay at sea for weeks or months, transferring catches between ships to obscure where fish were actually caught. Artisanal fishing boats, which number in the thousands in many coastal regions, often aren’t equipped with tracking systems and aren’t required to carry them. In Ecuador, for example, more than 5,500 small fishing boats operate with lines and surface gillnets, and none are required to transmit location data. That makes it nearly impossible for authorities to know where these boats go or what they catch.
Industrial fleets present a different challenge. They typically target high-value species like tuna, but genetic sampling has shown they routinely catch many other species that go unreported. Crew members often share lower-value bycatch with port workers and family, meaning it never enters official records. The gap between what’s reported and what’s actually pulled from the water is one of the core problems that fuels IUU fishing worldwide.
Flags of Convenience and Regulatory Gaps
One of the biggest enablers of illegal fishing is the “flag of convenience” system. Any vessel must be registered in a country, and that country’s flag determines which laws apply onboard. Some nations compete to attract vessel registrations by charging fees while offering little oversight or inspection. Ships registered under these flags operate under lax safety, environmental, and labor standards, and many fail to comply with international maritime conventions. The Marshall Islands is one of the most commonly used flags of convenience. Malta is another frequently cited example.
This system creates a loophole where fishing vessels can register in a country with minimal enforcement, then operate anywhere in the world with little accountability. These “shadow fleet” vessels may operate entirely outside the constraints of international law, making them effectively invisible to regulators. Closing this gap requires countries to hold flag states accountable for the behavior of vessels flying their flags, something that international agreements have been slowly pushing toward but that remains inconsistent in practice.
Satellite Tracking and Vessel Monitoring
The most powerful tool for detecting illegal fishing at scale is satellite-based tracking. The Automatic Identification System (AIS) broadcasts a vessel’s position, speed, and identity, and platforms like Global Fishing Watch compile this data into publicly accessible maps that show where fishing activity is happening in near real time. Researchers and enforcement agencies can trace a vessel’s entire voyage. One tracked industrial vessel, for instance, was followed across a 35-day fishing trip, while another was traced over 76 days before making port in Manta, Ecuador.
The limitation is that AIS can be switched off. Vessels engaged in illegal activity routinely go dark, disabling their transponders when entering protected waters or restricted zones. Some vessels never carry AIS at all. Combining AIS data with synthetic aperture radar (SAR) from satellites, which can detect vessels regardless of whether they’re broadcasting, helps fill this gap. Patrol aircraft, drones, and even machine learning algorithms that flag suspicious movement patterns are increasingly part of the enforcement toolkit.
DNA Testing to Catch Fraud in the Supply Chain
Illegal fishing doesn’t just happen at sea. A significant portion of it is laundered through the seafood supply chain, where illegally caught fish are mislabeled and sold as legally sourced products. DNA barcoding has become one of the most effective tools for catching this fraud. The technique works by sequencing a short section of a fish’s genetic code and matching it against reference databases that catalog thousands of species. Because the genetic differences between species are large and consistent, even processed or cooked fish can be identified down to the species level.
In a survey of 78 seafood products from markets and supermarkets in southern Italy, DNA barcoding revealed that about 6.4% were mislabeled, meaning the species on the label didn’t match the species in the package. Globally, mislabeling rates tend to be higher, sometimes exceeding 20% in certain markets. Two major databases, the Barcode of Life Data Systems (BOLD) and GenBank, allow researchers and inspectors to cross-reference results. If one database doesn’t return a match, the other often can. This kind of testing is relatively simple and cost-effective, making it scalable for port inspections and retail audits alike.
Marine Protected Areas Under Pressure
Marine protected areas (MPAs) are designed as refuges where fish populations can recover, but they only work if poaching is controlled. Data from one MPA studied over five years showed a dramatic spike in illegal fishing during the COVID-19 pandemic. Total illegal catch inside the protected area jumped from 56 kilograms before 2020 to over 1,140 kilograms afterward, a 20-fold increase. Across the entire study area, including waters outside the MPA, total confiscated illegal catch more than doubled from 853 kg to 1,922 kg.
The pandemic reduced enforcement patrols and economic pressures pushed more people toward poaching, but the pattern reveals a broader truth: MPAs need active enforcement to deliver conservation benefits. Without regular patrols, monitoring systems, and consequences for violations, designating a protected area on paper does little to protect the fish inside it.
International Agreements and Import Controls
The most significant international tool is the Port State Measures Agreement (PSMA), which requires countries to inspect foreign fishing vessels entering their ports and deny entry to those suspected of IUU fishing. By cutting off access to ports where illegal catches can be offloaded and sold, the PSMA targets the economic incentive behind illegal fishing. Over 70 countries have ratified the agreement, though enforcement varies widely.
On the import side, programs like the U.S. Seafood Import Monitoring Program require documentation tracing certain seafood products from the point of harvest to the U.S. border. The European Union has a similar catch certification scheme. Multilateral bodies including the Asia-Pacific Fishery Commission and the Southeast Asian Fisheries Development Center are working to build expertise in monitoring, control, and surveillance across regions where enforcement capacity is weakest. The goal is to make it financially unviable to sell illegally caught fish by blocking the main markets where it’s consumed.
What Consumers and Communities Can Do
Individual choices won’t solve IUU fishing, but they can shift market incentives. Buying seafood certified by organizations like the Marine Stewardship Council (MSC) supports fisheries that meet traceability and sustainability standards. Asking retailers where their fish comes from and how it was caught normalizes supply chain transparency. In coastal communities, reporting suspicious fishing activity to local marine authorities helps fill enforcement gaps, especially in and around protected areas.
Supporting policies that fund coast guard and fisheries enforcement, expand vessel tracking requirements, and strengthen import controls has a larger impact than any individual purchasing decision. The countries and regions that have reduced illegal fishing most effectively have done so by combining technology, regulation, and political will, not by relying on any single approach.