When the seagulls follow the trawler, it's because they think sardines will be thrown in to the sea.
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Eric was, of course, correct about gulls (although he let himself down by referring to "seagulls"):
But its worth noting this behaviour may well pre-date trawlers of all kinds. The gulls certainly weren't shy about following these guys whilst they were feeding either:
I was hoping on our whale watching trip to bag a few interesting pelagic birds too but alas it did not go so well. Yo can certainly make out a few different species working around this humpback though. The bulk of them look to be big American herring gulls but I think I can make out a ring-billed at the bottom right. We also had a few gannets plummetting into the mix from time to time. I'm not sure what the little white chap in the middle is but there is defo a shearwater of some species immediately above the whale's head. What species can you see?