New insights in the effects of bottom fishing on carbon release

May 12, 2023

In 2021 Nature published an article by Sala et al entitled "Protecting the global ocean for biodiversity food and climate". Among other things, this study made predictions about the impact of bottom fishing on seabed carbon stocks. The authors made bold claims of trawling releasing more carbon than air travel and less than 6% of the oceans remain free from human impact. Yesterday a new article was published in Nature by Jan Geert Hiddink et al that refutes much of Sala et al's methodology and results. Researcher Justin Tiano from Wageningen Marine Research co-authored this publication.

Hiddink et al (2023) argues that Sala et al. seriously overestimate the effects of bottom trawling. According to the researchers, their methods and results on carbon sequestration are flawed and make oversimplified assumptions. For instance, Sala et al. makes the assumption that carbon is as reactive in sediment as it is on the surface of the seabed, which they say is incorrect. Also, their models assume that carbon is not degraded in areas where trawling is not carried out. However, carbon almost always decomposes, releasing CO2 whether trawling is taking place or not.

Justin and his colleagues have worked on this topic for several years and have published several trawling experiments as well as modelling exercises on trawling effects on seabed carbon and nutrients. “Our work shows that if you trawl the seabed, the total breakdown of carbon (which causes CO2 release) in the sediment slows down because the fresh carbon from the surface is removed (most is resuspended and settles elsewhere).”

Effects still uncertain

When Sala et al. came out, it was an influential article. According to Hiddink et al. it resulted in people who build on their assumptions incorrect information on an already controversial topic. When extrapolated to a global scale, this leads to large overestimates of the impact of bottom fishing. "The science on the effects of bottom fishing on carbon and biogeochemistry is still quite uncertain. For instance, some studies show opposite effects of bottom fishing on seabed carbon. Therefore, it is still unclear whether countries are right to curtail or even ban bottom fishing in an effort to reduce carbon emissions."