cod has fallen on hard times in the baltic sea all too often they have fallen victim to overfishing the result test fishing vessels come back with empty nets the institute of baltic sea fisheries in the north german city of rostock operates three research vessels which spend sixty days a year out at sea in a large scale experiment the scientists in rostock measured and weighed five thousand cod they then injected them with a fluorescent dye before putting them back into the baltic. if analysts or fishing trawlers catch one of these marked cards they're supposed to send them to the institute in return they get twenty euros per fish the first specimens of began arriving in rostock. here bones known as bottle