The operation of sea ports is prohibited to private companies and other entities of the same nature, except under concession regime. The provision of cargo handling activities to the public is also considered to be in the public interest and can be provided by the following means: public service concession to stevedoring companies; licensing; or by the port authority.Otherwise, no specific licence or authorisation is required for maritime transport, only a registration with the regulator: maritime transport can only be carried out by shipowners registered with the Directorate-General for Ports, Navigation and Maritime Transport, the regulator. The continental cabotage is free for national and communitarian shipowners with ships flying the national flag or that of a member state, provided that the ships meet the necessary requirements for admission to cabotage in the member state in which they are registered. Island cabotage is free for national and communitarian shipowners with ships flying the national flag or of a member state, provided that the ships fulfill all the necessary requirements for being admitted to cabotage in the member state in which they are registered. Other relevant source on sea ports: Decree-Law 88-A/1997 regulating the access of private initiative to some economic activities, Adopted 25/07/1997, Last modification 11/06/2013, link: https://dre.pt/dre/legislacao-consolidada/lei/1997-107684396).