When anglers target large bluefin tuna for the purpose of selling them, they usually use a 130 class rod and reel,fished out of a swivel rodholder. (This 130 class equipment is too heavy for a stand-up angler to use with a belt and harness.)
The 130 means the reel is designed to use 130 lb test line although most anglers will use heavier line on the reels. The drag settings (40 lbs in strike and higher in full drag) are so high that you would be pulled out of the cockpit if you were directly connected to the rod and reel with a harness and belt, thus the gear is fished from a swivel rod holder.
Because the rod can't be used to pull the fish back to the boat,since the rod is in the holder, the reel is used as a "winch" to retrieve the line under tension. It is common practice to assist the reel by pulling the line from the first eye toward the reel to take off some of the pressure on the reel.
You are in less danger fighting a tuna this way than you would be in fighting one on lighter stand-up gear. - tom
That’s good info - thanks very much (and to the others posting answers as well). In the case of Marlins, I recognize that while they are fighters, they are also one-third the size of this monster tuna... so for me it was a question of sheer leverage.