The prospect of producing a steady—and highly profitable—supply of fatty Mediterranean bluefin set off a cascade of events that has proved disastrous. The Mediterranean fleet has increased its fishing effort threefold, with the bluefin flotilla now totaling 1,700 vessels, including 314 purse seiners. Compounding the problem, the advent of tuna ranching made it difficult for the European Union and national governments to enforce quotas. Bluefin are netted at sea, transferred into cages at sea, fattened offshore, killed offshore, and flash-frozen on Japanese ships. As Masanori Miyahara of the Fisheries Agency of Japan, and a former ICCAT chairman, told me: "It's kind of a black box."

The spread of tuna ranching means that bluefin are being wiped out at all stages of their life cycle. In Croatia, for instance, the industry is based almost entirely on fattening juveniles for two to three years, which means fish are killed before they spawn. Elsewhere, in places such as the Balearic Islands, large females, capable of producing 40 million eggs, are being wiped out. In just ten years, bluefin populations have been driven down sharply.

"What's happening is a bit like what happened to cod," said Jean-Marc Fromentin, a marine biologist and bluefin expert with IFREMER, the French Research Institute for the Exploitation of the Sea. "You don't see the decrease right away because you have had a huge accumulation of biomass. But it's like having a bank account, and you keep taking much more out than you're putting in."

At the heart of the fishing activity is Francisco Fuentes and his Cartagena-based company, Ricardo Fuentes & Sons, which, according to industry experts, controls 60 percent of the giant bluefin ranching business in the Mediterranean, generating revenues of more than 220 million dollars a year, according to industry sources. (A Fuentes spokesman said revenues are roughly half that.) In partnership with the Japanese giants Mitsui, Mitsubishi, and Maruha, the Fuentes Group—with the help of EU and Spanish subsidies—has bought the sea cages, tugs, and support boats needed for large-scale fattening operations. Fuentes & Sons also formed partnerships with French and Spanish companies that owned 20 purse seiners—five-million-dollar vessels equipped with powerful sonar systems and nets that can encircle 3,000 adult bluefin.

With the Fuentes Group and its partners leading the way, the bluefin fleet methodically targeted the fish in the spawning grounds close to Europe, then turned its attention to untouched areas. The richest of these de facto reserves was Libya's Gulf of Sidra. "It was the tuna aquarium of the Mediterranean," recalled Roberto Mielgo Bregazzi, a tuna ranching consultant who first visited the Gulf of Sidra six years ago. "I've never seen anything like it. The average size of bluefin was 600 pounds [270 kilograms]. It was one of the last tuna Shangri-las."

Mielgo Bregazzi, a dapper Spaniard and former professional diver who heads Advanced Tuna Ranching Technologies, has been on a mission to expose IUU—illegal, unreported, and unregulated—bluefin fishing. Drawing on a wide network of inside sources, as well as published information, he has written lengthy reports detailing the IUU bluefin business. Using arcane data such as the capacity and schedules of Japanese freezer vessels, he has shown that the Mediterranean tuna fleet has been seizing almost double its annual legal quota.

Mielgo Bregazzi said Ricardo Fuentes & Sons and a French partner have worked with a Libyan company, Ras el Hillal, to catch giant bluefin in Libyan waters. Mielgo Bregazzi said that Seif al Islam Qaddafi, the son of Libyan leader Muammar Qaddafi, has a financial interest in Ras el Hillal and has earned millions of dollars from the bluefin fishery. Mielgo Bregazzi calculated that, for the past four years, bluefin fleets netted more than 10,000 tons of bluefin annually in Libyan waters. Some of the catch is legal under quotas for Libyan, Spanish, and French boats, but much of it appears to be caught illegally.