I'm pretty sure you can seek the wake being left by the boat which is towing the line and shark fin in a couple of those shots. Look for the white water in front and to the left of the shark fin.
Hawaiian life-guards. It was really bad but in one episode they did this thing where they used their surf boards like rafts and took them to a nearby island. A shark followed them the whole way and one of the guys fell in. Nothing happened but it reminded me of this.