India, May 31 -- We know the ocean covers over 70% of the planet. What most of us don't really think about is that more than 60% of that vast expanse lies outside national boundaries, an unregulated immensity known as the high seas.

For most of human history, oceans have been mythologised rather than mapped. The dividing lines that do exist have been drawn in intriguing and somewhat arbitrary ways.

In the 18th century, for instance, a Dutch jurist proposed that a country's sovereign waters should extend as far as a cannon could fire from its coast, which turned out to be about three nautical miles (about 5.5 km). It was a brilliantly pragmatic solution: state control where defence was plausible, and freedom beyond.

The so-called "canno...