Wednesday, June 19, 2019

Study Shows Marine Fisheries Form a Single Network

A new international study concludes that the world’s marine fisheries form a single network, with fish valued in excess of $10 billion harvested annually outside of the country of origin.

Although fisheries are traditionally managed at the national level, this study by researchers in the United States and United Kingdom shows the degree to which each country’s fishing economy relies on the health of its neighbors’ spawning grounds.

In other words, it’s a small world network, the same phenomenon that allows strangers to be linked by six degrees of separation, while adding the potential risk that threats in one part of the world could result in a cascade of stresses, affecting one region after another.

Researchers from the University of California Berkeley, the London School of Economics and the University of Delaware said their study is the first to use a particle tracking computer simulation to map the flow of fish larvae across national boundaries to estimate the extent of larval transport globally.

“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 Kimberly Oremus, a study co-author and assistant professor at the University of Delaware’s School of Marine Science and Policy.

An estimated 90 percent of the world’s wild caught marine fish are harvested within 200 miles of shore, within national jurisdictions. Still some of these fish were carried far beyond their spawning grounds by currents in their larval stage, before they were able to swim, so while individual countries have set national maritime boundaries, the ocean is made up of highly interconnected networks where most countries depend on their neighbors to properly manage their own fisheries. Understanding the nature of this network is important in achieving more effective fisheries management, and essential for countries whose economies and food security are reliant on fish born elsewhere, researchers said.

Lead author Nandini Ramesh, a researcher of the Department of Earth and Planetary Science at the University of California Berkeley, said data from a wide range of scientific fields came together to make the study possible. “We needed to look at patterns of fish spawning, the life cycles of different species, ocean currents, and how these vary with the seasons in order to begin to understand this system,” Ramesh said. The study used data from satellites, ocean moorings, ecological field observations and marine catch records to build a computer model of how eggs and larvae of over 700 species of fish world-wide are transported by ocean currents.

“When fisheries are mismanaged or breeding grounds are not protected, it could affect food security half a world away,” said James Rising, assistant professorial research fellow at the Grantham Research Institute in the London School of Economics.

“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.”

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