We had the same thing happen when fishing Swiftsure bank in Canada in about 350' of water. I hooked into something really big and it was like pulling a barndoor off of the bottom. I would reel and reel and gain a little bit. I was really working up a sweat. We had to fire up the motor a couple of times as it headed for deeper water and was trying to spool me. There was absolutely no head shaking but there were some really good runs. I got it up almost close enough to see a half dozen times and it would head back down. I was almost ready to hand the rod off as my back was killing me. I finally got it up and it went under the boat. It finally came out and exploded out of the water. It looked like a funny colored marlin and impaled its nose into the back of the boat. I had to go out on the swimstep and work it out and try not to get knocked in. I bonked it so it didn't hurt me. Here it is. And to think you are allowed 200 of these a day in BC.