Humanity can make short work of the oceans' creatures. In 1741, hungry explorers discovered herds of Steller's sea cow in the Bering Strait, and in less than thirty years, the amiable beast had been harpooned into extinction. It's a classic story, but a key fact is often omitted. Bering Island was the last redoubt of a species that had been decimated by hunting and habitat loss years before the
explorers set sail.

As Callum M. Roberts reveals in The Unnatural History of the Sea, the oceans' bounty didn't disappear overnight. While today's fishing industry is ruthlessly...