There's not too much to comment on this, but I have a few suggestions.
The first is to check out several images of killer whales. It seems you've got a decent grasp as to how one looks, but everything seems a bit too bubbly and warbly at the moment. Fish are smooth and curvy, but they are also streamlined in an aerodynamic fashion. This is, of course, so they can swim proficiently.
Secondly, you might want to rethink the image entirely. The pose is pretty boring, and it might make incorporating new things to the image a bit more difficult. Is the whale going to be tiny or will it be gigantic? What are you going to put in the image to give the viewer that impression? Is the image going to have any perspective or is it going to be flat planed like a 2d platformer? Those are all questions you should be asking yourself before you go all gung-ho on the whale its self.