Seabed trawling is a significant contributor to global CO2 emissions

Bottom trawling releases about 340 million tons of carbon dioxide into the atmosphere each year, according to the first study to estimate these emissions. This represents almost 1% of the world's CO2 emissions, but is a major contribution that has been overlooked until now.

Trawling involves dragging a weighted net across the ocean floor to capture bottom-dwelling fish, crustaceans, and shellfish. Although this method of fishing is widely used around the world, it is controversial because the fishing gear damages undersea environments such as cold-water reefs. Some corals are thousands of years old.

“Trawling is a highly destructive fishing method as the nets and weights dragged along the bottom destroy marine habitat, which can take years to rebuild and recover.” he says. Micah Peck from the University of Sussex, UK, was not involved in the study.

It also stirs up sediment, releasing the oxygen needed by microorganisms to break down organic matter into carbon dioxide. Otherwise, these deposits could continue to accumulate for thousands of years, with the organic matter within them preserved by low-oxygen conditions. This means that carbon is effectively trapped.

In 2021, trisha atwood Researchers at Utah State University in Logan combined a study that looked at the amount of carbon dioxide released during trawling with data on the global scale of trawling. global fishing watch.The team concluded that released in large quantities into the seawater.

But the big unanswered question was how much of the CO2 released from the sediments would be emitted into the atmosphere.

“A lot of countries and different institutions started contacting us about that research,” Atwood says. “But they basically said, as long as it just stays in the ocean, we don't really care.”

So the team teamed up with researchers who had developed computer models of ocean circulation. According to these models, about 55 percent of the CO2 released into the water by trawling will be released into the atmosphere after nine years.

“I was surprised that more than half of them came out,” Atwood said. “And it shows up very quickly.”

According to the global carbon budget, the total amount of CO is₂ emissions from human activities Increased to 40.9 billion tons Therefore, if the team's estimates are correct, trawling accounts for about 0.8 percent of global emissions. Air and maritime transport: 2.8%.

Conservationists say the discovery strengthens the case for reducing trawling. “Many marine habitats are trawled at least once a year, resuspending sediment and releasing carbon into the atmosphere,” Peck said. “Banning destructive fishing practices is key to the future of healthy marine ecosystems and the marine ecosystems that depend on them.”

“Measures to reduce the carbon impact of trawling gear are urgently needed, but they must be done as part of a just transition,” said Gareth Cunningham. marine conservation association, is calling for a ban on trawling in so-called marine reserves around the UK. “There is no one-size-fits-all model and solutions will vary by location.”

However, not all researchers are satisfied with this number. “I'm very skeptical of their estimates,” he says. Jan Gerd Hiddink At Bangor University, UK.

Hiddink believes that much of the carbon that reaches the ocean floor is in forms that are difficult to decompose, such as bones, and that carbon is not released even when sediments are disturbed.Atwood's team is probably overestimate emissions Up to 1000x, he claims.

Atwood said this estimate is based on actual measurements. “We conducted a study to measure the amount of carbon dioxide emitted from the ocean floor in areas where trawling takes place,” she says.

She says that the amount of carbon dioxide emitted could be more or less than these studies suggest, although there is a lot of uncertainty because so few such studies have been done. says.

Mr Atwood says the government needs to start calculating the carbon footprint of trawling. “This allows us to decide whether emissions should be regulated,” she says.

What is clear is that Global Fishing Watch's trawling data is based on boats sending automatic signals to satellites, and many trawlers do not have such systems, so the extent of trawling remains under-studied. That means it's bigger than expected.

“We know that we underestimate the global scale and perhaps the intensity of trawling,” Atwood says.

The trawling industry also has an opportunity to sell carbon credits in exchange for reduced emissions, she says. “If you were to put a price on it in today's independent market, it's a $100 million market.”