Any county in the State of Mississippi bordering on the Mississippi Sound or the Gulf of Mexico in which county there is or may hereafter be located a municipality having a harbor or port of entry where commodities are exported to foreign nations, and where there is or may hereafter be maintained a channel and/or harbor or port to a depth of not less than twenty (20) feet, and where the board of supervisors of such county shall find and determine that public necessity and convenience requires the same, as evidenced by a resolution adopted and entered on the official minutes of such board, shall have a port authority to be known as the county port authority, but in any such county having four (4) incorporated municipalities therein, such county port authority shall be called and known as the development commission of such county. The county port authority shall be composed of seven (7) resident citizens of such county, who shall be qualified electors therein, but in any such county where a county development commission has been created, such county development commission shall be composed of twelve (12) resident citizens of such county, who shall be qualified electors therein. Such county port authority or county development commission shall have jurisdiction over the ports, terminals, harbors, channels, and passes leading thereto, and all vessels, boats, and wharves, common carriers and public utilities therein, using the same within the county, and not under the jurisdiction of any municipal port commission and exclusive of the jurisdiction of the port commission of any municipality in which a port of entry is located. But by joint resolutions adopted by the governing authorities of the county and the municipality, such county port authority or county development commission may be vested with joint and concurrent jurisdiction over all or any part of said port of entry, or the channels, harbors, or passes leading thereto, outside of the corporate limits of such municipality, and within such county.