Some idea's that came to mind were to have his boat partially sinking or to show some signs of wear and damage. I like rcartwright's idea about the barrel, I think it makes more sense than a mini boat (unless that is part of the story). You could also include a sinking ship in the background to help create more of a story to the piece.
His left arm is a little awkward in that position. It doesn't look as though he is rowing, rather than he is just using it to help the parrot. I think having the parrot on his head (as was mentioned) and having the bird holding the sail whilst he is frantically rowing away from sharks or something else dangerous, as they both are looking behind. You could even reverse the roles and have the parrot rowing instead whilst he is drink rum and relaxing, if you didn't want to include sharks 
It might be hard to show, but it could be cool to have them a wooden leg as the oar instead of an actual oar.