This photo is about 100 milli seconds from being perfect. i think if the seagull's head was visible then it would be so much better than it is now. So close.
But great work on getting that image. It is most definately a difficult task to shoot a bird in flight, either with a camera, a gun or in the case of a seagull, a chip.
Perhaps consider straightening the horizon and a tighter crop as well.
Well done.