I haven't found any references to Japan fishing in the Mediterranean, the only thing I could find is illegal fish farms in Croatia that farm fish to be exported to Japan and potentially "launder" illicitly caught Libyan fish [1].
While that is bad, it still is only a case of your typical piece of Balkan corruption - and actually being a Croatian citizen, I can only say one thing to these particular arseholes: jebo vam pas mater - and nowhere near comparable to what China is doing.