With a source of income I would cheerfully retire to that island and become those cats new keeper.
I have to wonder what will happen to them. The human population of the island is aging and there are no younger people. As all the old folks die off they will be left alone and they are used to being fed sometimes. The wildlife isn't enough to support feeding all of them I am sure. They've already altered a few of them for population control. I think the kindest thing to do would be to capture as many as they can, neuter them, and let the colony die out eventually. There's something like 150 cats. It would not be impossible and it would be better than letting them starve to death eventually...