F ish are an important source of high-quality food, particularly for the poor, for whom small quantities often provide the only protein in a diet based on a staple food such as rice. Fishing is an important source of employment for many coastal people1. The commercial value of fish presumably far outstrips the value of any other wild game that humans hunt. Fishing also represents a considerable recreational value. Finally, the stock of fish is a vital indicator of the state of the environment; fish live in the water that covers most of Earth’s surface and also is the final deposit for a large share of industrial and agricultural pollution.