It is indeed a small world after all. The world’s marine fisheries form a “small-world network” and every year, over $10 billion worth of fish are caught in countries outside the ones in which they are spawned, according to a new study published on 20 June in Science (1).
Fisheries are typically managed on a national level as a local resource. More than 90 per cent of the world’s fish is caught within a few hundred kilometres extending off the shores of coastal nations. However, the world’s fisheries are highly interconnected and form what the authors refer to as a “small-world network”.
The researchers from the University of California, Berkeley, the London School of Economics, and the University of Delaware, led by Oceanographer Dr Nandini Ramesh, brought together expertise in oceanography, fish biology, and economics to explore the international connectivity of more than 700 commercially fish species harvested within almost 250 national fishing grounds.
More specifically, they used computer simulations based on particle tracking to build a global network of fish larval dispersal by modelling how eggs and larvae of hundreds of fish species travel around the world via ocean currents before they can swim.
The simulation was based on the life cycles of different species, including when and where they spawn, and the speeds and directions of ocean currents. The data came from satellites, ocean moorings, ecological field observations, and marine catch records.
The study revealed the incredible interconnectedness of fisheries around the world. Every year, countries like Indonesia, Norway, and Mexico harvest hundreds of thousands of tonnes of fish originating beyond their jurisdiction, whereas major spawning hubs include Brazil, Barbados, and Kiribati.
The new findings underscore a need for global cooperation in managing fish stocks — which provide millions of people with food and livelihoods — since most of the fish caught in local jurisdictions originate elsewhere. This means national economies that rely on fishing must also depend on other countries to maintain crucial spawning grounds.
Furthermore, threats in one region could have a cascading effect on other regions. Overfishing, pollution, and other impacts on the environment could dramatically reduce global fish stocks. And certain countries would be hit particularly hard if spawning grounds in other countries were cut off.
This first-of-its-kind map will help identify hotspots of regional interdependence where cooperation is needed most urgently. For instance, the researchers found that counties in the tropics are most at risk – especially in terms of food security and jobs. For example, larval inflows from other jurisdictions sustain around one-third of livelihoods in Guyana and Suriname in the Carribean and 22 per cent in Comoros in the east African archipelago.
And in some of these countries, hundreds of millions of people rely on the fishing industry. Therefore, more effective and cooperative fishery management is urgently needed. The authors hope this new information will bring awareness of global interconnectedness to policymakers. “This is an important first step”, says Ramesh. “This is not something people have examined before at this scale.”
(1) Ramesh, N., Rising, J.A., and Oremus, K.L. The small world of global marine fisheries: The cross-boundary consequences of larval dispersal. Science (2019). DOI: 10.1126/science.aav3409