The Board shall investigate conditions in which it has an interest within the Port District, the enforcement of its ordinances, rules and regulations, and the action, conduct and efficiency of all officers, agents and employees of the Port District. In the conduct of such investigations the Board may hold public hearings on its own motion, and shall do so on complaint or petition of any municipality within the District. Each member of the Board shall have power to administer oaths. The secretary, by order of the Board, shall issue subpoenas to secure the attendance and testimony of witnesses, and the production of books and papers relevant to such investigations and to any hearing before the Board or any member thereof.