The reefs near Cabo Pulmo, in Mexico's Sea of Cortez, once swarmed with fish—until, because of overfishing, they didn't anymore. In 1995, a marine-protected area called Cabo Pulmo National Park was established there, and commercial fishing was prohibited. Since then, fish populations have more than quad­rupled. Here, a school of bigeye trevallies checks out a diver.

This article appeared in the November/December 2018 edition with the headline "School of Thought."