The Small World of Global Marine Fisheries: The Cross-Boundary Consequences of Larval Dispersal

Marine fisheries, which supply food and livelihoods to millions of people, are typically managed at the scale of Exclusive Economic Zones (EEZs). However, many fish populations are connected beyond EEZ boundaries. In the early stages of the life cycle, fish spawn that cannot yet swim are dispersed by currents. While adult fish migrations between national territories can be tracked, the extent of larval dispersal across international boundaries is not well-understood.

In this study, we combine oceanographic and life history data for over 700 species of commercially harvested fish to estimate their connectivity across 249 EEZs and construct a network representing the larval flows connecting nations. The countries that depend heavily upon their neighbors for inflows of spawn risk losing a part of their catch if the fisheries in the source EEZs, which are outside of their jurisdiction, are poorly managed. We quantify these risks in economic terms and identify regional hotspots of risk for catch, GDP, fishery employment, and food security.

We find that the world’s fisheries are highly interconnected, forming a scale-free, small-world network. This indicates that international cooperation in the management of fish stocks should be a high priority. We find that over $10 billion in annual catch from 2005 to 2014 is attributable to these international flows of larvae. The economic impact of these dependencies is felt most heavily in the Tropics.