Ever see a public pool with a "No-Pee Zone"? Us either. However No-Human-Zones in California seem to work
Many scientists feel that limiting human access to nature (in general) is a good thing, and that the only real hope for the world is to dramatically limit mankind's access to the world's resources. This image - in case you've never seen it - is from the United Nations and shows an American where specific "usage" corridors are established between large urban areas and human access denied anywhere except for those corridors.
We've personally felt that "Marine Protected Zones" were much the same as making a "No-Pee" section in a public pool. You can stop people (commercial and recreational anglers, divers, and boaters in the case of MPZs) from doing something in one part of the pool, but the pool is the pool.
Maybe that's not the case, however according to this article from K93 Radio.
“We’re already seeing larger fish and more diverse fish populations within those marine protected areas,” said Tom Maloney, the executive director of the California Ocean Science Trust, which helped put out the report.
The report they are referring to is here in Acrobat PDF form and is from State of California South Coast.