I hope those cats are getting enough vitamins/minerals in there diets. One would think an all-seafood diet wouldn't be rich in certain vital amino acids, and there can't be that many rodents or small birds in a place with that many cats. Also, with cats being the territorial creatures with the habit of killing even more when they're well fed, I would think that a true "cat heaven" would give them more space than that. I also kinda hope that at least a certain amount of the population is getting neutered/spayed, I mean, with such a high population already and no predators the resources can't likely sustain many more than what the fishermen are already giving them...
Oh, god! I just imagined a dead cat attracting crows...Which didn't last long themselves.
...Leave it to me to look at the downside of such a wonderfully magical place and ruin the mood.
I'd been sorta planning a trip to Japan next summer, I think need to visit this place while there if it's at all possible.