The equatorial South Atlantic, specifically the region between the latitude of the Benlomond’s sinking and the position of his rescue off the Brazilian coast, is not the most productive fishing environment in the ocean. It lacks the cold-water upwelling systems that make coastal Pacific zones extraordinarily rich in marine life. But it is not empty. The surface layer of tropical open ocean supports a food chain that includes flying fish, dorado (also called mahi-mahi or dolphinfish), and various species of tuna and bonito, all of which can be taken with line fishing from a surface vessel. Seabirds — petrels, boobies, and frigate birds among them — follow the fish concentrations and are present throughout the tropical Atlantic.
The specific genius of what Poon Lim built, evaluated against this ecology, is that he constructed a complete supplementary food system from the materials at hand. The hook was wire from a flashlight. The line was hemp rope. The bait was hardtack crushed into a paste that had enough of a scent trail to attract interest. The seabird trap was a pile of seaweed positioned near a dead fish, taking advantage of bird behavior patterns that a person who had spent his formative years near the sea would recognize. The shark luring exploited the blood smell that sharks detect over remarkable distances. Each step of the system fed the next: caught fish provided bait to attract birds, birds attracted sharks, sharks provided additional blood as a liquid source and dried meat as a protein bank.