Seriously, a seagull managed to stop your repair work? That's next level annoying. @irisjenkins has a point about them always causing trouble. I can't believe the crew had to coax it down from a piling. Old-school tools come with their own brand of chaos, but this is wildlife interference. Never heard of a chalk line becoming bird bait before.
Secure the chalk reel to a bucket or tool bag with a short rope before you snap a line near the water. Those gulls see the string flying and think it's food every single time. I started using a bright pink line because it looks less like a fish or a worm to them. Keep any snacks sealed up too, since they'll go after anything shiny or moving. A heavier braided mason's line can also help, it doesn't blow around as easy in the wind.