What are the motifs in Cod: A Biography of the Fish That Changed the World by Mark Kurlansky?

The cod recovery is a recurring idea. The book presents conservation science as a secondary theme and gradually introduces the concept throughout the middle half of the text. Chapter 12 in particular focuses on the theme that cod might not be able to rebound, even if humans stop fishing for it. After the Atlantic cod fishery collapses of the early 1900s, many reasonably theorized that the best course of action would be to simply stop taking so many cod out of the oceans. Harvesting fewer fish would mean that more would survive to reproduce and, so the theory goes, within a half-dozen or so years, cod populations should return to normal.