The district courts of the United States shall have jurisdiction over all offenses against this chapter and of all suits of a civil nature arising thereunder, whether the infraction complained of shall have been committed within the territorial waters of the United States or on board a vessel of the United States outside of said waters: Provided, That in case such infraction is committed outside of the territorial waters of the United States the vessel on board of which it has been committed is a vessel of the United States. From the decrees and judgments of the district courts in actions and suits arising under this chapter appeals and writs of error ¹ shall be allowed as now provided by law in other cases. Criminal actions and proceedings for a violation of the provisions of this chapter shall be commenced and prosecuted in the district court for the district within which the offense was committed, and when not committed within any judicial district, then in the district court for the district within which the offender may be found; and suits of a civil nature may be commenced in the district court for any district within which the defendant may be found and shall be served with process.