Odd sight - a seagull catching a fish

You don't see it that often at sea - but today I saw a seagull catch a pretty decent sized fish in the Regent's Canal, and swoop up to a nearby roof garden to try to eat it. A couple of other people stopped to wonder at ... well perhaps that there actually are any fish in the canal in the first place - and perhaps also how a seagul managed to spot it. But then I guess that's what seagulls do ...