Ocean trawling releases more carbon from seabeds than previously thought

April 2021: A new model estimates that ocean trawling could release more carbon annually from seabeds than the global aviation industry. Released carbon poses a significant threat to marine habitats and the ocean’s ability to act as a carbon sink. To avoid negative impacts on marine ocean habitats, increased ocean temperatures, and contributions to ocean acidification, the findings support the idea of establishing Marine Protected Areas in 30% of the ocean by 2030.

Information

A new model published in advance of the 2021 UN Convention on Biological Diversity (COP 15) suggests that ocean trawling releases 1.47 billion tonnes of aqueous CO₂ from the marine soil annually. Ocean trawling is the practice of dragging nets along the ocean floor to catch fish. In light of these recent estimates, ocean trawling would release more carbon dioxide into the atmosphere that the annual emissions of the global aviation industry. Data suggests that trawlers are dredging up roughly 1.3% of the seafloor each year. This number only represents 0.02% of all sedimentary carbon in the ocean, yet, this is equivalent to 20% of the atmospheric CO₂ estimated to be released annually by soil activities such as farming. The majority of trawling occurs in less than 4% of the ocean and is concentrated to sovereign fishing waters of costal nation including China, Russia, Italy, and the UK.

Implications and opportunities

Carbon released from seabeds can have negative impacts on the marine environment, contributing to ocean acidification and oxygen depletion. In addition, it may impact the ocean’s ability to act as a carbon sink and store carbon released by terrestrial activities. It supports efforts for strategic conservation planning, including concepts to protect up to 30% of the ocean by 2030 to improve biodiversity conservation, food provisioning in fishing waters, and carbon storage. Establishing such Marine Protected Areas (MAP) could contribute to marine habitat conservation and improve the productivity of costal fisheries; a topic which is likely to be a feature of this year’s COP 15 hosted by China. The model estimates that by reducing trawling activities, up to 90% risk in carbon disturbance from the seabed could be eliminated. However, establishing MPAs requires a significant effort from international organisations and cross-national collaborations to reduce human impact on oceans at scale.

Limitations

The provided estimates should be seen within the context of their data limitations and variability.

Sources

Hodgson, C., (2021). Ocean trawling emits as much CO2 as global aviation, study finds. Available at: https://www.ft.com/content/54857423-cc4e-43a4-b8bd-7fb23f2f6abc

Sala, E., Mayorga, J., Bradley, D. et al. Protecting the global ocean for biodiversity, food and climate. Nature592, 397–402 (2021). https://doi.org/10.1038/s41586-021-03371-z