BARBATE, Spain — The fishing boats, swaying in the narrow strait that connects the Atlantic to the Mediterranean, maneuvered one recent morning around an intricate architecture of nets they had laid as a trap. Then the fishermen lifted just one section from the water, heavy with their prize.

Dozens of bluefin tuna rose to the choppy surface, thrashing wildly until, exhausted and asphyxiated, the fish gave up the fight, and the fishermen hoisted them onboard by the tail.

This trap-fishing method, known as almadraba in Spanish, is considered the oldest form of industrial fishing in the world, dating 3,000 years to the Phoenicians.

Even if the tuna’s final struggle and killing with a knife can appear violent, the almadraba has been praised as a sustainable way of fishing. While the boats and nets have been modernized, the method itself has remained largely the same over millenniums.