In the days when the population around the Mediterranean was too small to make an impact and there was no rampant Japanese market the Mediterranean Sea had vigorously healthy tuna stocks. The fish would enter the Straits of Gibraltar in late spring and fill larders from Andalucia to Sicily and beyond. On the coast of Catalonia tuna fishing was an activity in which whole communities would participate. Villages were often built slightly inland on raised ground but when the tuna came the population would decamp to the beach and set up shop for the duration.
The method of fishing was called 'Almadrava'* and the technique was as follows. At a chosen beach a net would be set diagonally with respect to the land, with one end fixed to the sand and the other rowed out to sea and anchored. The fast swimming fish, entering the net, would find themselves forced ever nearer the beach until they reached the inevitable cul-de-sac. Here the villagers would wade in with harpoons while others in boats would attack the fish from behind. The word 'Almadrava' comes from Arabic and means 'place of battle'. Almadrava fishing was nothing short of a massacre. The moment of thrashing silver fish, wild water, sunlight, bronzed limbs and gushing blood is vividly depicted in Salvador Dalí's 'la pesca del atún' (Tuna fishing) painted on the Costa Brava over the summers of 1966 and '67 and capturing on canvas one of the last seasons of almadrava fishing.
Almost all of this abundant harvest of tuna would be conserved in olive oil. Originally in glass jars and later in tins. The fish tripe, salted and dried, would sustain the population over the winter. Nowadays, while you can buy tuna flesh in tins very cheaply and indeed, it's not enormously expensive even fresh, the dried tripe, tasty though it is, commands a price far beyond its worth. But such is the madness of the world we have made for ourselves.
*In Southern Spain tuna is still fished with a method called 'almadraba' (note the b rather than v that distinguishes the Catalan). The Andulucian almadraba is set at sea, as opposed to from the beach, the nets forming a maze that leads the fish to a central area. Boats converge and a net floor is raised bringing the tuna to the surface where they are killed and hauled aboard. Again it is a place of battle.