Atlantic bluefin tuna are one of the world’s largest, fastest, and arguably tastiest fish. Prized for sushi as well as tuna steaks, these metallic-hued predators can weigh in at more than a thousand pounds. And the illicit market for them can mean big money.

A multi-country organized crime ring dealing in more than 2,000 tons of tuna annually, or more than 10 times the weight of a blue whale, was recently uncovered by the European Union’s law enforcement agency. Europol’s explosive findings suggest that the volume of illicit bluefin tuna sold in Europe is likely double that of the legal tuna trade.

Following a months-long investigation across Spain, Portugal, France, Malta, and Italy, Spanish officials arrested 79 people and seized more than 170,000 pounds of tuna. Police also picked up seven luxury vehicles and half a million Euros (about $575,000 dollars) in cash. Announced this week by Europol, the arrests took place in Spain at the end of June.

View Images Police examine tuna stored in the back of a transport truck. Photograph Courtesy Europol

The tuna probe was called Operation Tarantelo, a nod to a particularly valued cut from the back of the fish, says Jose Alfaro, Europol’s Environmental Crime Specialist. The operation, which was led by Europol but conducted in partnership with involved countries, concluded that these illegal activities involved multiple fishing companies, as well as a network of people who apparently forged documentation and smuggled fish across the region.

A substantial portion of the recovered tuna was dumped on the side of the road by panicked truck drivers as coordinated raids took place across Spain, Portugal, and Italy, says Alfaro.

The news has sent shock waves through the conservation community. “That there is illegal fishing taking place on such an enormous scale caught us by surprise, and it’s quite alarming,” says Paulus Tak, who leads the Pew Charitable Trusts’ delegation at the International Commission for the Conservation of Atlantic Tunas (ICCAT), the global body that sets limits on how much tuna can be fished each year and where.

Investigators believe that the tuna trafficking ring had operated for many years, netting more than 12 million Euros annually by selling up to 5.5 million pounds of undocumented fish. European authorities tracing the illegal operation also found that fish typically were caught in Italian and Maltese waters and imported into Spain from France.

This prodigious level of illegal fishing has the ability to undermine the sustainability of fish stocks, Tak warns. The revelation about the sheer scale of illegal tuna fishing will also be a key factor in future negotiations for legal bluefin tuna fishing levels, he says.

Spanish authorities first contacted Europol about a glut of bluefin tuna showing up in its seafood markets last spring. Investigators soon found that in numerous instances fishing vessels were holding their official, legal tuna catch onboard and transporting larger quantities of undocumented catch in false bottoms under the decks of their vessels. Truck drivers transporting both the illegal and legal tuna would show paperwork saying they had, maybe, four tons of fish when in reality they had 14 tons, says Alfaro, who was present when one such truck pulled up to a major fish storage warehouse in Malta.

Because many of the trafficked fish in this underground network were not stored in sanitary conditions and were not quickly frozen, they’ve caused at least eight instances of food poisoning, Alfaro says.

Bluefin tuna are commonly used in sushi and sashimi, and Japan is the largest importer. But the European market is also significant—in Spain and Italy, bluefin is commonly eaten as steaks or in chunks.

Our appetite for these fish threatens their survival. A decade ago, an ICCAT review dubbed management of bluefin tuna an “international disgrace.” At that point, tuna stocks had dropped so low that the fish were considered a potential candidate for a global trade ban under the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES), the agreement that regulates the wildlife trade.

Bluefin Tuna Caught on Film Feeding for the First Time

Yet, according to Tak, a flurry of more robust protections for the fish, including strict catch limits and better tracking through the implementation of an electronic catch documentation system, have helped them. In 2005 the adult population, estimated by weight, for the eastern stock of Atlantic bluefin tuna—the biggest group of tuna—was about 300,000 tons. It’s now estimated to be up to 530,000 tons, according to ICCAT. (Pew says those numbers come with a high degree of uncertainty.)

Tak says the new Europol findings raise questions about the extent of the bluefin tuna comeback and suggest that they’ve been more heavily fished than previously realized.

When you think of organized crime, you may not typically think of environmental crime, but this investigation makes clear that it’s happening, Alfaro says. “For me, this is the most important thing.”