The harbour porpoise Phocoena phocoena is one of the smallest odontocetes, rarely reaching a length of 1.8 meters. Harbour porpoises are the most numerous cetacean in the North Sea. Over the past years, the harbour porpoise population has shifted from the northern part towards the southern part of the North Sea. This increase in porpoise numbers in the southern North Sea resulted in an increase of strandings and by-catch along the Dutch coast. This increase raised concern about the conservation status of the harbour porpoise. In order to develop effective protection measures, a better understanding of the porpoises’ function within the marine ecosystem is needed. Therefore diet studies are necessary. It is not possible to study the diet of porpoises in the wild with visual observations, due to their small size and elusive behaviour. Therefore, stranded porpoises are used.