What PinWheel means in regards to tuna fish:

​Once the Tuna Fish develops high levels of hypoxia, it will change its fighting tactic, coming to the surface and then going deep again. With the ensuing fatigue, it can no longer maintain an upright orientation and will begin to succumb to line pressure by laying over. This results in a circling swimming motion, which is the first indication of a tired fish. if you can create a slight heads-up attitude by pumping the rod, the fish will swim itself in circles toward the surface. ​