No mercury in Billfish, and it is delectable-and you suck if you kill one to eat it. 2400 feet is pretty deep, and I don't have the charts for the area, but I will assume there are some pretty sharp rises in the immediate area. I wouldn't be surprised if they caught a 2,000# mamma-blue in that area; they are there.
BTW, when I was fishing the tourny circuit, most of the tournaments had prize pools over well over a half a mil, with at least 2 going over 1 million bucks, back in the early 80's when a million dollars was worth something. Never did win one, though, although we placed in the money a couple of times.
edit-here are some pics of that size fish:
http://www.bigmarinefish.com/photos_blue_marlin_pg1.html