The controversial practice of dragging weighted nets along the ocean floor, sometimes known as bottom trawling, could be responsible for a significant source of carbon pollution, according to a new study.
The study found that between 55%-60% of the carbon dioxide produced underwater by bottom trawling will make it into the atmosphere within nine years.
It estimates the practice means up to 370 million metric tons of carbon dioxide are being released into the atmosphere each year, and that trawling in East China, Baltic, North Sea and Greenland Sea have largest impact on the climate.
The study was conducted by a team of climate and ocean experts from Utah State University, NASA Goddard Institute for Space Studies, the University of California Santa Barbara, Columbia University, James Cook University and National Geographic Pristine Seas.
The researchers used ocean models and data on bottom trawling activity globally between 1996-2020 to calculate how much of the carbon dioxide produced by the activity ultimately enters the atmosphere.
Dr. Trisha Atwood of Utah State University and National Geographic Pristine Seas said in a statement, bottom trawling “unleashes plumes of carbon”, which otherwise would be safely stored on the ocean floor.
“Our study is the very first to show that over half the carbon released by bottom trawling eventually escapes into the atmosphere as carbon dioxide over the span of about ten years, contributing to global warming,” added Dr. Atwood.
Last year, the sportswear company Patagonia launched a campaign, which called on European leaders to end the practice of bottom trawling, starting with an immediate ban in marine protected areas and inshore zones.
Patagonia EMEA’s environmental initiatives manager, Gina Lovett said in an email, while it is difficult to grasp the complexity of the marine carbon cycle, the report authors have highlighted trawling’s effect on ocean acidification and its ability to absorb carbon.
Ocean acidification is a change in the pH of seawater, which is normally around neutral.
Many scientists have noted there has been a reduction in the pH of the ocean over an extended period of time, caused primarily by uptake of carbon dioxide (CO2) from the atmosphere.
“Taking a step back, what we know is that bottom trawling is harmful on so many environmental and social counts,” added Lovett.
“Now we know there is another charge: a concerning carbon impact from churning up the seafloor. By continuing to turn a blind eye to all of these counts, national decision makers are willingly colluding on marine and climate destruction.”
Dr. Max Valentine, campaign director at the non-profit organization Oceana, said in an email bottom trawling is an “incredibly destructive process” which is often likened to clear-cutting a forest.
“The seabed is what we call a carbon sink. It’s a place where carbon gets sequestered long term, which is critically important in regards to climate change,” she added.
So, when you have bottom trawling occurring, disturbing these areas and mixing up the sediments, there are cascading impacts for our global ecosystem.
“Globally, there aren’t many limitations on bottom trawling. Few countries ban this process, and there are even fewer rules regarding this fishing practice on the high seas,” said Dr. Valentine.
And Charles Goddard, head of the Back to Blue non-profit initiative said in an email this new study corroborates what many in the ocean community have been concerned about.
Goddard said oceans are “our silent saviour as our largest carbon sink”, but as carbon emissions are absorbed, from without and within, its chemistry begins to change as the ocean acidifies.
“It is vital now that the emissions released by bottom trawling be accounted for in climate action plans, and that greater consideration be given to banning this indiscriminate practice, which also destroys essential marine habitats and species,” he added.
