I've seen a lot of seagulls too. These looked like something that fits the broad category of gull or tern... a large, grey and white salt water coastal bird.
That's the thing... Marine coastal birds aren't migratory. The V-formation thing is a migrating habit.
Like when the swallows are carryin' coconuts from the tropical regions suspended with a bit of string... the African swallows, mind you, not the European swallows.