The technique, in its most simple iteration, consists in setting up net barriers so as to trap the tuna when they migrate into the Mediterranean Sea from the Atlantic Ocean (February to July), on their way to spawn and
until recently, on their return journey, ("al revés"); the bycatch contains, among others, bullet tuna (auxis rochei), little tunny (euthynnus alletteratus), Atlantic bonito (sarda sarda), bigeye tuna (thunnus obesus) and swordfish (xiphias gladius).
A similar technique exists in Sicily known as mattanza (a borrowing from the Spanish word matanza, meaning 'slaughter'), introduced either by the Moors during Sicily's own Islamic period or by the Spanish afterwards.