The climax of a story is when the action reaches the highest point of tension. In The Old Man and the Sea, the climax occurs when Santiago kills the marlin and ties it to his boat as he heads to shore. As he heads home, sharks devour his marlin. This is the point at which the action, which has been heading towards Santiago's capture of the marlin after many fruitless days at sea, is at its height. Santiago has gotten what he wanted, but he loses it quickly, as the sharks quickly devour the marlin, leaving only a skeleton. When Santiago arrives home, he falls fast asleep. When Manolin, his young friend and former fishing partner, awakens Santiago, they agree to fish together again. This returns the story to the beginning of the action.
The climax of the novel is when Santiago kills the fish. This is when his fortunes take a turn for the worse. The sharks start to attack the fish, leading to the resolution (denouement) of the novel where Santiago must watch helplessly as the sharks strip the fish of its meat. Santiago then experiences the revelation that he will fish successfully again. He recognizes his skill as a fisherman for the first time, and this brings him hope.
The climax of The Old Man and the Sea occurs as the marlin circles the skiff while Santiago slowly reels him in. Santiago nearly passes out from exhaustion but gathers enough strength to harpoon the marlin through the heart. For Santiago, this is the ultimate accomplishment of vitality before dying.