The image (atmosphere) looks too washed out. Dolfins have shining skin and a lighter color. Logically the water would be in a movement, so that the man cannot stand relaxed in his boat; they are not in a dolfin show but far in the sea. The water drops would spring much highter.

Do some real water splashes (big ones). I have a tutorial for it, see link at bottom.
Give more highlight to the dolfins and change the black Poser highlight to white. Give some reflection. Use terrains (dunes) for the water. Equilibrate the light in creating some shadowless square spots coming from the opposite side to the sun. Make the light in the atmosphere editor a bit darker.

I can send you the above scene (without the dolfin, of course, but with the spot)if you like to study it.

Guitta

tutorials for beginners