The card's objective is: "Control more Ports than each other player"

So, do i have to have a ship in the port or do i simply need to control the area that the port belongs to no matter if my port is empty of ships?

How do you interpret this while playing?

Controlling the adjacent land area is how you control the port, doesn't matter if you have ships in port or not.

http://www.boardgamegeek.com/thread/1187839/mercantile-ventures-objective

Thank you for the reply. That's how we currently play, but we were a little unsure.