Why your fish’s carbon footprint may be bigger than you think

Why your fish’s carbon footprint may be bigger than you think

Nearly a quarter of all wild-caught seafood is brought to market using a fishing method called bottom trawling, in which weighted nets are dragged along the sea floor to catch cod, haddock, hake, shrimp and many other species.

Bottom trawling is controversial because heavy trawls damage seabed habitats and indiscriminately kill marine life that fishermen don’t want – what the industry calls “bycatch.”

A new study published today in the journal Frontiers in Marine Science adds another environmental problem to that list. As the nets capture fish, they also raise a significant source of greenhouse gas emissions.

“When you drag nets and gear along the ocean floor, it can lead to increased carbon dioxide that eventually reaches the atmosphere,” said Trisha Atwood, an associate professor at Utah State University. Newsweek. Atwood is also a marine researcher with National Geographic’s Pristine Seas program, which supported the research.

Fisherman, fishing vessel, fishing in the Atlantic Ocean
A French fisherman sorts the catch on the fishing vessel Nounoute during a fishing trip off the coast of Ouistreham, northwest France. A new study shows that bottom trawling can stir up carbon on the seafloor, ultimately adding carbon dioxide emissions to the atmosphere.
Charlie Tripalo/AFP via Getty Images

Atwood explained that carbon-rich sediments stirred up by trawling interact with microorganisms in the water, producing carbon dioxide. She and her colleagues are the first to measure the amount of carbon dioxide reaching the atmosphere.

“About 55 to 60 percent of the carbon dioxide from bottom trawling will reach the atmosphere, and it does so very quickly,” Atwood said. “She’s doing it in nine years.”

Researchers estimate that globally these emissions amount to about 370 million metric tons per year. To put this in context, this equates to roughly 10% of total global emissions from land use changes in one year.

“The carbon footprint of bottom trawling extends far beyond just the gas they burned to reach their fishing grounds,” Atwood said. It has been estimated that the carbon dioxide produced by bottom trawling is about twice as much as produced by fuel combustion in the 4 million vessels in the global fishing fleet.

These emissions from bottom trawling were missing from overall emissions estimates and climate action plans for countries with fishing fleets. The study identified the East China Sea, Baltic Sea and North Sea as areas where emissions from bottom trawling are particularly high.

Companies and fisheries managers can now also take CO2 emissions into account in their broader environmental assessment of bottom trawl fishing.

Atwood brought up another idea that could have an impact on the decisions hunters make. Any reductions in carbon dioxide emissions from fishing could become a way to make money in the voluntary carbon credit market.

Carbon credit markets allow companies that cannot yet reduce their emissions to purchase credits that represent proven proof of emissions reductions made by others. Such markets have had problems, especially with verifying emissions reductions, but they offer the advantage of financing low-carbon practices that would otherwise incur very high costs that people could not afford.

“If we can get fishing activity into the voluntary carbon market, there could potentially be money that can help fisheries upgrade their gear,” Atwood explained. “It could help stimulate innovation around better ways to catch fish.”

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