Conservation news

Ocean currents spin a web of interconnected fisheries around the world

  • Most marine catches are made within a given country’s territorial waters, but the fish most likely originated in spawning grounds in another country’s jurisdiction, a new study shows.
  • The modeling of catch, spawning and ocean current data shows that the dispersal of baby fish caught by ocean currents creates an interconnection between global marine fisheries.
  • The finding highlights the need for greater international cooperation in protecting marine ecosystems everywhere, as an estimated $10 billion worth of fish spawn in one country and are caught in another every year.

Chances are the locally caught fish you bought down by the wharf was spawned thousands of miles away, migrating on ocean currents, a new study has found.

An estimated 90 percent of marine catches are caught within 200 miles, or 320 kilometers, of countries’ shores, but they most likely originated in spawning grounds under the jurisdiction of a different country, according to the study published June 21 in the journal Science.

Analyzing data of catch and known spawning grounds of more than 700 fish species, coupled with ocean current data, the paper’s researchers developed a computer model to show where the various species tended to be born and caught.

The simulation then showed that the dispersal of baby fish caught by ocean currents created an interconnection between global marine fisheries, the study said.

“Now we have a map of how the world’s fisheries are interconnected, and where international cooperation is needed most urgently to conserve a natural resource that hundreds of millions of people rely on,” said co-author Kimberly Oremus, an assistant professor at the University of Delaware’s School of Marine Science and Policy.

The global network of flows of fish spawn across international boundaries. The circles represent ocean territories and the lines indicate flows between them. The lines are curved such that the clockwise direction represents flows from source to sink. Image by Nandini Ramesh/University of California, Berkeley.

Any two given countries are connected by an average of five degrees of separation, with effects from fishery disruptions — habitat destruction, overfishing, and sea warming — that take place in one country spreading to other nations, both near and possibly on the other side of the world, according to the researchers.

This ripple effect could theoretically look like this: If there’s a decline in a species’ spawning population in Indonesian waters, the catch in Vietnam, Singapore, Malaysia, the Philippines, Australia, and India’s Andaman and Nicobar Islands will most likely drop.

According to the study, the spawning grounds around Japan, Alaska and China are the three regions that currently contribute the most catch to other countries, through their productive spawning populations. Each contributes about 1 million tons to other countries’ catches.

Indonesia has the most landed value attributable to other countries, meaning much of its catch originates from the spawning grounds of its neighbors, such as Singapore, Malaysia, the Philippines and Papua New Guinea, according to the researchers.

“This is something of a double-edged sword,” said lead author Nandini Ramesh, a postdoctoral researcher at the University of California, Berkeley.

“On one hand, it implies that mismanagement of a fishery can have negative effects that easily propagate to other countries; on the other hand, it implies that multiple countries can benefit by targeting conservation and/or management efforts in just a few regions.”

The finding highlights the need for greater international cooperation in protecting marine ecosystems everywhere — such as large marine ecosystems and marine protected area networks — as an estimated $10 billion worth of fish spawn in one country and are caught in another every year, the authors say. Global fisheries production in 2016 was valued at $130 billion, according to the U.N.’s Food and Agriculture Organization.

“This allowed us to talk about how vulnerable a nation is to the management of fisheries in neighboring countries,” Oremus said.

A spawning aggregation of Nassau groupers. Image by Alexander Tewfik for WCS.

According to the study, the risks to nations’ economies and labor forces are generally highest in the tropics. This is due to a combination of factors, such as there being a large number of small, coastal countries close together in regions with relatively fast ocean currents; economies that rely heavily on marine fisheries; and populations with a high percentage of workers employed in fishing-related jobs.

“Our hope is that this study will be a stepping stone for policy makers to study their own regions more closely to determine their interdependencies,” Ramesh said. “This is an important first step. This is not something people have examined before at this scale.”

Citation:

Ramesh, N., Rising, J. A., & Oremus, K. L. (2019). The small world of global marine fisheries: The cross-boundary consequences of larval dispersal. Science364(6446), 1192-1196. doi:10.1126/science.aav3409

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