What about this for an idea: Every boat must have onboard video (CCTV) facing the deck and other important places, which transmits live images via satelite to Wellington. Just like webcam pictures. Each picture would be encoded with GPS data so they could see what was being caught, where and when.
I don't know what it costs in wages etc to put observers on a boat, but surely the cost of video surveillance wouldn't be far off, and it never sleeps...