bugger.
Are you sure it was them though ? As you said I'd have thought any one with an country background would have just had the lot away - for himself or his mates.
Could there be someone mink watching ? or whatever it would be called. We had a chap round by us, university professor, who was studying mink and we suspected that he'd released some near the pens so that they'd have a good food supply to get established.
Need to hide your traps a bit better mate - particularly for a while as they'll be looking for more. Try building a few 'dummy' ones and see what happens.