Hi Graham,
Sometimes all it takes to improve a photo is just the slightest movement.
In this instance I would have suggested moving downwards with the camera about 10 centimetres and that would have improved the photograph rather considerably.
As I look at the two gulls my eyes are constantly drawn to the dark mass of weed and rock behind them. If you had moved down the slightest amount the background would have been less distracting and, at a guess, the image might have become more engaging.
Never be shy to move about with camera; remember, the background is often just as important as the subject.
Cheers,
Anthony