Kaizoku Ouji

Kid was brought up on a small island which floats on the Carribean Sea. He lives a pleasant life with many animals as his companions. However, this changes when he learns that his dying father is not his real father. Before he passes away, his foster father reveals to Kid that his real father is actually Captain Morgan, the pirate who rules the seven seas.
Kid decides to set off in search of his real father, only to learn about his death. Other pirates began to hunger for the title of ruler, one of them being the notorious pirate Tiger Hook. In order to protect the seas, Kid became the pirate king of his father's ship.
(Source: Anime News Network)