Source: The Great Interpretation of Dreams (Ibn Sirin)
A seagull in a dream is a merchant man who travels by sea. Seeing it indicates travel and sustenance.
Source: Perfuming Humanity in the Expression of Dreams (Al-Nabulsi)
A seagull indicates a man who travels frequently. Whoever sees himself catching one will gain sustenance from travel.
Source: Signs in the Science of Expressions (Ibn Shaheen)
A seagull is interpreted as goodness. Whoever sees himself owning one will attain goodness.