Kokua Line: How many feral cats live on Oahu?

Question: Does anybody know how many feral cats there are on Oahu? Does anybody count them? Sadly, we see cats that have been hit by cars, which upsets my children. There is a colony in our area, and the lady who feeds them does keep track of them and gets them fixed, but she has no idea how many cats there are on the rest of the island.