It may not even be food related but simply that they may be attracted to the movement of the boat or they may confuse it with a big fish--pretty much like dogs barking at and running after cars. In Spanish we say that dogs run after cars because they have a "cat" in the trunk. The word cat in Spanish is the same as the word for jack.aargh57 said:Free Chile,
Just wanted to point out that most birds have a very poor sense of smell, so while they may very well be attracted to a fishing boat for the other reasons you mentioned (sounds and sight of the baits(although I think they probably recognize the boats themeselves as you will see gulls flying towards boats from a distance that they couldn't see the baits, not to mention the fact that often times the fishermen aren't putting the baits out yet and the gulls are still hanging around)) the smell is probably not one of them.
http://www.earthsky.com/shows/shows.php?t=20041002
I'm just thinking of other possibilities besides the next meal idea. The simple reality is that we don't know why animals behave in a particular way in many cases.