I would use the same plan I use for other critters--put some attractive
food in the same place every day (or several times a day). When
somebody comes and gets is soon after it is placed, start placing and
move a little ways away, and work on getting closer over time.
Don't ever do anything suddenly and don't do anything that looks like a
threat.
I wouldn't think it would take long--my limited experience with gulls is
similar to my more extensive experience with 'Jays--the ones that are
acclimated to humans will steal what you are eating, given half a chance.
Here is an article I pointed to a while ago--in the first 'graph you can
sort of imagine what must have gone on.
http://creagrus.home.montereybay.com/corvids.html
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