(CN) – Researchers from the University of California, Berkeley, the University of Delaware and the London School of Economics mapped how fish babies and eggs flow with ocean currents from one region to another, showing the ways that marine disturbances, such as pollution or overfishing, can send ripple effects in a study released on Thursday.
“The biggest surprise for me is how closely countries are connected,” said co-author James Rising, of the London School of Economics’ Grantham Research Institute, in an interview.
“On average, any two countries are connected by five ‘degrees of separation.’ That means that fishery disruption that starts in one country can spread to the other side of the world, if it causes a cascade of disruption in neighboring countries,” Rising said.
Published Thursday in the journal Science, the study color-codes models of the fish larvae flows, presenting the ocean as a small-world network, filled with connecting clusters of fisheries. Also considered: The economic implications of the interconnections.
“Marine fisheries are an important source of jobs, revenue, GDP and food security for many nations around the world,” co-author Kimberly Oremus, of University of Delaware’s School of Marine Science and Policy, told Courthouse News. “We wanted to measure how fish populations are connected across national jurisdictions.”
The study considered 747 groups of fish with commercial value. Around the world, 90% of valued fish get harvested within 200 miles of shore. Each nation and region wins some and loses some when it comes to stocks of fish.
Researchers used a particle tracking computer simulation and a complex web of data, which included ocean current variables and information on where and for how long species spawn, to show hubs of larvae as well as connectors that indicate net flows.
Each year, an estimated $10 billion worth of fish are spawned in one country and caught in another.
“For every caught species in every country, we divided the market value of that catch between all the spawning regions that flow into it,” Rising said.
The three fish-rich areas from which the most outflows occur are Alaska, China and Japan. The nations that capture the most fish from elsewhere are the ones with the biggest fisheries, such as China, Russia and the United States.
Researchers also identified “hotspots” where fishers are dependent on the management of fisheries in other nations, leaving their job and food security largely out of their control. Especially vulnerable are people in the tropics, as well as some European nations.
“There are also dependencies that arise because of adult fish movement, international treaties, ecological interactions and changing habitats due to climate change,” UC Berkeley’s Nandini Ramesh, lead author, told Courthouse News. “Ultimately, we hope that this kind of knowledge will be used in developing sustainable fishery management strategies.”