Peter, you are right about the traditional kapu practices, and indeed this is not just a Hawaiian feature, but now a common feature of nearly all Pacific island cultures.  The other critical component to traditional area management is a chief or designee whose job it is to know the health of the system by moving about and observing it and speaking with folks, so that appropriate and adaptive behavior can be set forward by the chief.   Such practices are not that uncommon now in modern fisheries, and on a much larger scale as well, plus there are kapu zones for the aquarium fishery in Kona that are now called "Fish Replenishment Zones".  

When there were fewer people, more observant chiefs, and a benign world, this highly flexible system probably worked just fine.  However, as you yourself point out, we are in a different world now.  There are many many more people.  Fishing pressure is much higher due both to the number of fishermen and the technology now available.  It's different.