Well, the jokes are really quite bad that have been featured there so far, way beyond groaner level. Anyhoo, with this particular one I think the 'joke' is that Dutch people are so 'economical' (? I can't really find a good translation for 'zuinig') that they even won't dump fishwaste overboard, or something :-?. Therefore not attracting seagulls?
In jokes Dutch people have this characteristic in common with Scots, i.e. not willing to spend money and stuff. As I said, this particular one isn't remotely funny.
Oh and 'herkennen' is indeed 'to recognise'.
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Hang on: © 2004 Moppen.be. It's Belgian humour, no wonder it's not funny :-P.