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To supply the world's sushi markets, bluefin tuna are fished from the Mediterranean at four times the sustainable rate.

They are then fattened up in 69 ranches (here, fresh from the wild in a pen off the San Pedro del Pinatar, Spain) that have sprung up in the Mediterranean over the past decade. 'Bluefin tuna continue to grow throughout their long lives, crisscross entire oceans annually and are capable of swimming nearly from the equator to the poles,' says Brian, who describes them as 'one of the most incredible animals that has ever lived.' But their populations are crashing through overfishing, legal and illegal, and despite calls for a temporary ban on global trade to let numbers build up, tuna continue to be hunted - probably to extinction in the very near future.