gday mate,
a FAD_ is a Fish aggregating device, as you said it is basically a bouy attaced to the bottom which floats on the surface. when the warm currents run down the coast pelagics and species like dolphin fish follow and they are attracted to floating objects and congregate around them as do bait fish, kings etc. people usually troll the vacinty, cast lures and baits and come up with fish its a very simple way to get dolphin fish and other species (not at the moment in sydney though as the warmer currents havent arrived and stayed around, the 22 degree mark water temp is ideal while the water is approx 18-20 in some areas so not warm enough.) hope this helped oh and the coordintes for fads are on fisheries websites , usually the wider fads hold the better quality fish and there are also many private fads around for you to find (just floating objects really).
hope this helps
cheers pk