Bottom Trawling Releases Significant CO2, Contributing To Climate Change And Ocean Acidification

Bottom trawling, a fishing method that involves dragging heavy gear across the seafloor, has long been criticized for its destructive impact on marine habitats. This study found that this practice also has significant implications for our climate. The research, conducted by an international team of scientists, found that bottom trawling releases alarming amounts of stored CO2 from marine sediments, contributing to atmospheric CO2 levels and ocean acidification.

The researchers used a combination of methods to investigate the impact of bottom trawling. They examined satellite data from Global Fishing Watch to estimate the intensity and extent of bottom trawling. They also analyzed sediment carbon stock estimates from a previous study. Finally, they ran carbon cycle models to simulate the transport and fate of trawling-induced CO2 release over time.

They found that between 1996 and 2020, trawling activities are estimated to have released a staggering 8.5-9.2 Pg (petagrams) of CO2 into the atmosphere. This equates to an annual emission of 0.34-0.37 Pg CO2, which is comparable to 9-11% of global emissions from land-use change in 2020 alone.

One of the most striking findings is the rapid pace at which trawling-induced CO2 enters the atmosphere. The study found that 55-60% of the CO2 released by trawling is transferred from the ocean to the atmosphere within just 7-9 years. The remaining 40-45% of CO2 released by trawling stays dissolved in seawater, contributing to ocean acidification.

The carbon cycle models allowed the team to track the movement of CO2 through ocean currents, biological processes, and air-sea gas exchange. This revealed that even areas without intense trawling, such as the South China Sea and Norwegian Sea, could be affected by CO2 transported from other regions. 

The findings suggest that reducing bottom trawling efforts could be an effective climate mitigation strategy. Because the atmospheric CO2 effects of trawling are relatively short-lived compared to other carbon sources, policies limiting trawling could lead to significant reductions in emissions.

The study emphasizes the importance of protecting marine sediments as critical carbon reservoirs. In addition to their role in supporting biodiversity, marine sediments play a vital role in regulating our climate by storing vast amounts of organic carbon. The authors note that their estimates are likely conservative, as data limitations and knowledge gaps prevented them from fully accounting for the global extent of trawling. They call for further research to refine our understanding of trawling’s impact on sedimentary carbon stocks and the processes driving CO2 release.

The authors strongly recommend that advocates and policymakers prioritize the protection of marine sediments as a critical component of both ocean conservation and climate change mitigation efforts. By working together to reduce destructive fishing practices like bottom trawling, we can safeguard the life in our oceans while also helping to secure a more stable climate for future generations.