What did the decline of porpoise (e. g. dolphins) bones in garbage piles indicate

This indicated that the area on Easter Island had become less populated and people were no longer thriving there at that time. The palm tree had become extinct because it had been harvested too much. This is also probably due to an over population of rats, which ate the seeds of the palm. Once the palm tree was extinct, the people no longer had wood to build boats and necessary tools to thrive. The people on Easter Island lived off a diet of porpoise, and when the people declined, they were no longer there to eat the porpoise thus the decline of bones in garbage piles.