Seafloor Trawl Fishing May Release as Much Carbon as Air Travel

A new study finds the carbon released when bottom trawlers stir up the seafloor is equal to the emissions of the entire aviation industry

Gulls feeding on dead starfish dumped on quay from fishing trawlers in Hokkaido, Japan
The marine sediments that bottom trawlers stir up like underwater rototillers are the largest storehouse of carbon on the planet. Photo by: Education Images/Universal Images Group via Getty Images

Bottom trawlers collect fish and shrimp from the world’s oceans by dragging massive, weighted nets across the seafloor. In pursuit of their targeted catch, these indiscriminate nets destroy corals, sea sponges and anything else in their path, leaving scoured tracts and stirred up sediment in their wake. Beyond the untargeted marine life or bycatch that ends up caught in the nets, the practice also alters the sea bed’s structure, chemistry and ecology in ways that may take decades or centuries to heal.

Now, a new study finds that when bottom trawlers churn up the seafloor they release a gigaton of carbon dioxide into the world’s oceans every year—a massive total equal to the entire aviation industry’s annual emissions, reports Catrin Einhorn for the New York Times.

The marine sediments that bottom trawlers stir up like underwater rototillers are the largest storehouse of carbon on the planet, reports Karen McVeigh for the Guardian. When this stored carbon dissolves into the oceans it contributes to ocean acidification and reduces the ocean’s already taxed ability to pull carbon dioxide from the atmosphere. Some portion of this released carbon may even enter the atmosphere, though researchers are still working out just how much. According to the Times, preliminary data suggest that a “large proportion” does.

China, Russia, Italy, the U.K., Denmark, France, the Netherlands, Norway, Croatia and Spain are the ten countries responsible for the most carbon released by bottom trawling, according to the study. In total, the study also finds bottom trawlers plough across 1.9 million square miles of the seafloor every year.

These grim figures, published this week in the journal Nature, are part of a sweeping global assessment of how protecting the marine environment could benefit biodiversity and humanity while combating climate change. Beyond detailing the damaging impacts of unregulated and indiscriminate fishing practices the report also presents a map showing which areas of the ocean are most vital to protect.

Released in advance of upcoming United Nations negotiations on biodiversity in Kunming, China, the report’s authors say their findings lend support to the target of conserving 30 percent of Earth’s land and oceans by 2030. That goal, known as 30x30, has increasingly broad support from nearly 60 countries and the new study suggests protecting 30 percent of the world’s oceans from fishing, drilling and mining would not just boost biodiversity and help the marine system sequester carbon, it would also increase the productivity of global fisheries, according to the Times.

“The worst enemy of fishing and food security is overfishing,” Enric Sala, a marine biologist who directs National Geographic’s Pristine Seas project and led study, tells the Times.

“Usually we’ll talk about these things separately,” Rashid Sumaila, an economist studying fisheries at the University of British Columbia who was not involved in the study, tells Lili Pike of Vox. “Adding the three together is new. They are all actually interconnected, and they are all pointing to the same thing: We’re putting too much pressure on our natural systems.”

Currently, just 7 percent of the world’s oceans are protected and less than 3 percent receives the strictest protections. The new analysis led by Sala includes an algorithm to help policy makers identify the parts of the seas that will deliver the greatest benefits if they are conserved. The tool can be customized by placing different weight on each of the three goals of conserving biodiversity, increasing seafood production and mitigating climate change, according to the Guardian.

“There is no single best solution to save marine life and obtain these other benefits. The solution depends on what society—or a given country—cares about, and our study provides a new way to integrate these preferences and find effective conservation strategies,” Juan Mayorga, a marine data scientist at the University of California, Santa Barbara and co-author of the report, tells the Guardian.

For example, protecting a carefully selected chunk equaling just 4 percent of the oceans would slash the carbon disturbed by bottom trawlers by 90 percent. On the other hand, if increasing the productivity of fisheries is the primary goal, the study found that 28 percent of the oceans would need to be protected with no fishing zones.

“The results of this high-level analysis convey a very hopeful message,” Josephine Iacarella, an aquatic ecologist at Fisheries and Oceans Canada who was not involved in the study, tells the Times. “Currently each nation does it based on their own priorities. To raise that to a global level is more challenging, but that discussion can be started by papers like this.”

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