Large numbers of harbor porpoises are caught in fishing nets, because the porpoises feed on schooling fish such as herring and mackerel, in relatively shallow coastal waters. They are also affected by increasing pollution in coastal waters, and are considered vulnerable or threatened in many parts of their range. Learn more about the Phocoena phocoena, more commonly known as a Harbor Porpoise, in this easy-to-read species overview by the Smithsonian's National Museum of Natural History.