On a warm July morning, in the sapphire-colored waters west of the Spanish island of Ibiza, six purse-seine boats from three competing companies searched for giant bluefin tuna. The purse seiners—named for their conical, purse-like nets, which are drawn closed from the bottom—were guided by three spotter aircraft that crisscrossed the sky like vultures.
In the center of the action was Txema Galaz Ugalde, a Basque marine biologist, diver, and fisherman who helps run Ecolofish, one of 69 tuna ranching, or fattening, operations that have sprung up throughout the Mediterranean. A small company, Ecolofish owns five purse seiners. Its main rival that morning was the tuna baron of the Mediterranean, Francisco Fuentes of Ricardo Fuentes & Sons, whose industrial-scale operations have been chewing up giant bluefin stocks.
I was with Galaz on La Viveta Segunda—a 72-foot (22 meters) support vessel that was part of the fleet of dive boats and cage-towing tugs following the purse seiners. Around 11 a.m., the spotter planes spied a school, setting the purse seiners on a 19-knot dash. The stakes were high. Even a small school of 200 bluefin can, when fattened, fetch more than half a million dollars on the Japanese market. Galaz watched through binoculars as an Ecolofish seiner reached the school first and began encircling it with a mile-long (1.6 kilometers) net.
"He's fishing!" Galaz shouted. "He's shooting the net!"
It was not an unalloyed victory. Before Ecolofish's boat could complete its circle, a Fuentes seiner rushed forward and stopped just short of the unfurling net. Under one of the few rules that exist in the free-for-all for Mediterranean bluefin, this symbolic touch entitled the competing boat to split the catch fifty-fifty.
Over the next several hours, Galaz and his divers transferred the fish—163 bluefin, averaging about 300 pounds (135 kilograms)—from the purse-seine net into the sea cage, a large holding pen about 160 feet (50 meters) in diameter, with a sturdy plastic frame supporting a heavy mesh net. As the pen, already brimming with a thousand bluefin caught in the days before, was aligned with the purse-seine net, Galaz invited me into the water.
Swimming with the tuna was mesmerizing but unsettling. Giant bluefin are, as Galaz put it, "like missiles, prepared for speed and power." Their backs were battleship gray topped with a saw-toothed line of small yellow dorsal fins. Their sides had the look of battered chrome and steel; some bore the streak of an electric blue line. The larger fish, weighing more than 500 pounds (230 kilograms), were at least eight feet (two meters) long.
One giant bluefin—some 300 pounds (135 kilograms) heavier and two feet (0.6 meters) longer than most of the others—caught my eye. It was not swimming endlessly with the school in a clockwise gyre. Instead, it darted in different directions, sullen and aggressive, nearly brushing against me as it scanned me with large, black, disk-shaped eyes. There was something else: a stainless-steel hook embedded in its mouth, trailing a long strand of monofilament line. In recent weeks, this fish had lunged at one of the thousands of baited hooks set by a longline vessel. Somehow, it had broken free.
After untying the large mesh gates on the pen, Galaz and his divers began herding fish. Peeling off from their gyre, the bluefin whizzed into the cage like torpedoes. The fish with the hook in its mouth was one of the last to leave, but eventually it shot up from the depths and into the cage, dragging a diver who had hitched a ride on the line.