Trawling activities, in addition to causing damage to the seabed and losses in species that are not the target of fishing, trigger processes that increase the concentration of carbon dioxide in the atmosphere (causing climate change) to a level that up to Now it had not been sufficiently taken into account, according to a study led by experts from Utah State University (United States), NASA's Goddard Institute for Space Studies and National Geographic Pristine Seas, the results of which have been published in the journal Frontiers. in Marine Science (January 18).
Most studies on the causes of climate change and the actions necessary to control it are based on direct emissions of greenhouse gases into the atmosphere, from fossil fuels, deforestation and other sources, recall the authors of the new study. The analysis of data presented now indicates that bottom trawling causes a strong climate impact because the action of dragging large nets with weights along the seabed causes the release of carbon found in the sediments, which passes into the water. and then into the atmosphere in the form of carbon dioxide.
A previous study had found that some of the carbon in disturbed sediment is converted to carbon dioxide underwater. The current study reveals that between 55% and 60% of the carbon dioxide produced underwater by bottom trawling will reach the atmosphere within nine years.
It is estimated that the amount of carbon that bottom trawling releases into the atmosphere each year doubles the annual emissions from fuel burning by the entire world's fishing fleet – some 4 million vessels.
"We have known for a long time that dragging heavy fishing nets (some the size of ten 747 airliners) across the ocean floor destroys marine life and habitats," said Dr. Trisha Atwood of Utah State University and National Geographic Pristine Seas.
"We have recently discovered that bottom trawling also releases plumes of carbon, which would otherwise be safely stored for millennia on the ocean floor. Our study is the first to show that more than half of the carbon released by Bottom trawling eventually escapes to the ocean floor atmosphere as carbon dioxide for about ten years, contributing to global warming. Like the destruction of forests, seafloor excavation causes irreparable damage to the climate, the society and wildlife.
The study, "Atmospheric CO 2 emissions and ocean acidification due to bottom trawling," was conducted by a global team of climate and ocean experts from Utah State University, Goddard Institute for Space Studies NASA, the University of California at Santa Barbara, Columbia University, James Cook University and National Geographic's Pristine Seas.
The researchers used data on bottom trawling conducted globally between 1996 and 2020 and sophisticated models to calculate how much carbon dioxide produced by bottom trawling ultimately enters the atmosphere. This study builds on recent foundational research that finds that the amount of carbon dioxide released into the ocean by bottom trawling is greater than the annual carbon emissions of most countries and on the same order of magnitude as annual carbon dioxide emissions from global aviation.
The new research identifies ocean areas where carbon emissions from bottom trawling are especially high, including the East China Sea, the Baltic Sea and the North Sea, and the Greenland Sea. The researchers conclude that Southeast Asia, the Bay of Bengal, the Arabian Sea, parts of Europe and the Gulf of Mexico are also likely important sources of carbon emissions due to trawling, but we currently lack sufficient data on the extent and the intensity of bottom trawling. in these areas.
“Right now, countries are not factoring in the significant carbon emissions from bottom trawling in their climate action plans,” said Dr. Enric Sala, National Explorer in Residence and CEO of Pristine Seas. "Our research makes clear that addressing these and other ocean emissions is critical to slowing global warming, as well as restoring marine life. The good news is that reducing carbon emissions from bottom trawling will deliver immediate benefits. The bad news is that delaying action guarantees that emissions from trawling will still be leaking into the atmosphere a decade from now."
The new study also assesses what happens to the carbon that is trapped in ocean waters after bottom trawling is done. It concludes that between 40% and 45% of the total carbon released from the ocean floor by trawling remains in the water, leading to increased localized ocean acidification. This increase in acidity damages the plant and animal life in the area where fishing activity takes place.
"There are more problems with bottom trawling than just carbon impacts: biodiversity and sustainability, for example," said Gavin A. Schmidt, director of NASA's Goddard Institute for Space Studies. "But this 'marine deforestation' is large enough to be noticed and evaluated. Hopefully, this can lead to policy efforts that attempt to maximize benefits across all impacts."
