Potential conflicts between fishing and ocean carbon sequestration

[Press release] - Published on March 26, 2025 in Press Corner, Science-Society

An international team led by researchers from the University of Montpellier, the CNRS and the University of California has mapped the potential areas of conflict between two major contributions of the ocean to human societies: fishing and carbon sequestration. A few months ahead of the opening of the^3rd United Nations Ocean Conference, to be held in Nice in June 2025, their work, published in the journal One Earth, opens up original avenues for adapting fishing practices.

Fishing and ocean carbon sequestration, a long-neglected link

On land, the impact of agriculture on the carbon sinks represented by forests is now well quantified. On the other hand, the link between fishing and carbon sequestration in the oceans remains less well understood. Through their carcasses and the carbon-rich faeces they produce, which sink into the abyss, fish contribute directly to carbon sequestration in the deep ocean. Ocean soils, for their part, store vast quantities of carbon accumulated over time in sediment - carbon known as blue carbon. The problem is that fishing, by removing large quantities of fish and damaging the seabed through techniques such as benthic trawling (a method of dragging a trawl-like net in direct contact with the marine sediment), drastically limits the oceans' capacity to trap this blue carbon.  

Although the antagonism between blue carbon and the socio-economic benefits of fishing (jobs, food security, etc.) has been pointed out for several years, the surface area and location of these potentially conflicting zones have been little known until now. This new study reveals that they cover 15% of the ocean, spread across international waters and coastal areas.

Fish play a crucial role in the ocean carbon cycle, contributing directly to carbon sequestration in the deep ocean through the regular production of fecal pellets and carbon-rich carcasses that sink into the abyss, trapping the carbon they contain for centuries. IRD - Ifremer

International waters, a major conflict zone

International waters, which are not under the direct authority of any state and where deep-sea fishing takes place, account for almost 50% of the conflict zones identified in this study. "Yet other studies have shown that deep-sea fishing is recognized as contributing very little to global food security, as it is mainly carried out by developed countries with no food insecurity problems," point out the study's authors. "Our study therefore provides a further argument for applying the precautionary principle, i.e. limiting deep-sea fishing until its impact on carbon sequestration has been assessed", they conclude.

Benthic trawling and carbon sequestration, a coastal conflict

While protecting the high seas will have little impact on overall socio-economic objectives such as food security, the story is quite different with benthic trawling in coastal environments. Indeed, although the areas of conflict between sediment carbon sequestration and benthic trawling cover just 3.8% of the ocean, over 56% of benthic trawl catches take place there. "This shows that major conflicts can arise if these areas are protected from trawling. These conflicts are all the more significant when the areas identified concern food-insecure countries," the researchers add.

There are solutions

The study shows, however, that solutions do exist. "Let's take a simple example. The coasts of Argentina have been identified as conflict zones, because they are of vital importance for carbon sequestration in the sediment, but also for trawling. However, some species can also be fished with gear that does not come into contact with the sediment. This is the case, for example, with Argentine hake, which is caught using benthic trawls that come into contact with the sediment, but which can also be caught using pelagic trawls or line trawls. Thus, changing catching methods would make it possible to maintain the jobs and socio-economic benefits derived from the Argentine hake fishery, while preserving the carbon stock present in the sediment", say the authors of the study.