According to EU Directive 98/41 it is mandatory, for safety reasons, to list by name all passengers on every sailing.
Passengers are advised to provide their travel agency with a telephone number (preferably a mobile phone number) so they can be contacted in case of emergency, e.g. cancellation of departure due to bad weather conditions etc.
Passengers must also present their identity card or any other official documents (i.e. passport, driver's license etc.) as a proof of identity to the vessel's authorized personnel or Port Authority, during ticket control at embarkation.