herring feed by gulping in seawater as they swim and filtering out minuscule zooplankton. They will search thousands of miles for these drifting beds of food, which means that a spot that had always been teeming with herring may suddenly one day be devoid of a single one, and they might not return to that spot for years. For the peoples of northern Europe who depended on herring, this could be a cataclysmic event, often blamed on the sins of the village folk. In the Middle Ages, adultery was thought to be a major cause of the herring leaving.
