What happens when the fish begins to circle?

The old man's line began to tighten when the fish began to circle, but it was a large circle. Later the fish started hitting the wire leader with its spear, something the old man worried would lead to its jumping. Then the fish began to rise higher in the water, and the old man knew the time was coming to use his harpoon. Eventually, the old man was able to harpoon the fish through its shoulder.