When did Karana stop counting the moons? Why do you think this happened?

From the text:

Until that summer, I had kept count of all the moons since the time my brother and I were alone upon the island. For each one that came and went I cut a mark in a pole beside the door of my house. 'There were many marks, from the roof to the floor. But after that summer I did not cut them any more. The passing of the moons now had come to mean little, and I only made marks to count the four seasons of the year. The last year I did not count those.