Trawls fuel climate change

Trawls fuel climate change

Fishing with bottom trawling releases large amounts of CO2. © piola666/ iStock

It is well known that fishing with huge bottom trawling nets harms the ocean and its inhabitants. But it has other serious consequences, as researchers have now discovered. The trawls also ensure that carbon stored in the seabed escapes and rises into the atmosphere in the form of CO2. Every year, trawling is responsible for the emission of 370 million tons of CO2, twice as much as the fuel burned by global fishing fleets.

Bottom trawls are intended to catch fish that are close to the seabed, such as cod. The heavy nets plow through the sand, leaving a path of destruction in their wake, including destroyed coral gardens and seagrass meadows. In addition, all sorts of bycatch ends up in the nets, which can be up to 20,000 square meters in size, for which the encounter is often fatal, including starfish, crabs and snails.

Trawls produce CO2

But bottom trawls cause even more serious damage. It has been known for a few years that the heavy nets stir up the sediment on the seabed so much that the carbon stored in it is released again and partly converted into harmful carbon dioxide. The amount of CO2 released in this way could be similar to the annual carbon dioxide emissions from global aviation. This means that bottom trawling would be responsible for more CO2 than most countries.

But what happens to the carbon dioxide? How much of it stays on the ocean floor or in seawater and how much actually rises into the atmosphere? Researchers led by Trisha Atwood from Utah State University have now examined this in more detail for the first time. To do this, they entered data on global bottom trawling between 1996 and 2020 into special models and used them to carry out various simulations. In this way, Atwood and her team were finally able to track the distribution routes and quantities of trawl CO2.

“Irreparable damage to the climate”

The result: 55 to 60 percent of the carbon dioxide produced underwater by bottom trawling enters the atmosphere within nine years, as the researchers report. This corresponds to up to 370 million tons of CO2 per year. For comparison: the fuel combustion of all four million fishing vessels in the world emits just half of this amount. But the remaining 40 to 45 percent of carbon dioxide that does not rise into the atmosphere also causes damage, as Atwood and her colleagues explain. This residual CO2 remains in the water and leads to local acidification. This increased acidity in turn endangers the flora and fauna in the affected area.

“Similar to the destruction of forests, scraping the ocean floor causes irreparable damage to the climate, society and wildlife,” concludes Atwood. A significant amount of this destruction is actually taking place right on our doorstep. As the researchers have determined, carbon emissions from bottom trawling are particularly high in the Baltic and North Seas. The East China Sea and the Greenland Sea are also among the main sources of these fishing-related CO2 emissions. In order to effectively counteract climate change, a rethinking of fishing is necessary, says senior author Enric Sala from the National Geographic Society. “The good news is that reducing carbon emissions brings immediate benefits to bottom trawling. The bad news is that delaying action will ensure that emissions from trawling will still be released into the atmosphere ten years from now,” said Sala.

Source: National Geographic Pristine Seas; Specialist article: Frontiers in Marine Science, doi: 10.3389/fmars.2023.1125137

Recent Articles

Related Stories

Stay on op - Ge the daily news in your inbox