Bottom Trawling and the Seabed Carbon Puzzle: When Fishing Can Warm the Climate
Bottom trawling is one of the oldest and most productive forms of commercial fishing, but it is also one of the most controversial. Giant nets and weighted gear are dragged across the seafloor to catch species such as cod, flatfish, and shrimp, and in the process the heavy equipment rakes through sediments that cover vast areas of the continental shelf. Those sediments are not inert. They hold enormous reservoirs of organic carbon that have been accumulating for millennia. When the gear disturbs them, some of that carbon can be released into the water column and eventually into the atmosphere as carbon dioxide, potentially adding to the greenhouse gases already driving climate change.
New research published in the Journal of Applied Ecology adds considerable nuance to this picture. The research team, drawing on sediment cores, trawling effort maps, and process-based biogeochemical modeling, argues that the climate impact of bottom fishing is not a single, simple number. It depends on where trawling takes place, how intensively, how deep the disturbance reaches, and what kinds of sediment and microbial communities are present. Disturbing muddy seabeds rich in ancient organic matter can liberate carbon that would otherwise have remained sequestered for centuries. Disturbing coarser sandy bottoms, on the other hand, often has a much smaller effect because those areas store far less organic carbon in the first place.
The analysis outlines several competing mechanisms that can unfold when a trawl door slices through the seabed. Resuspended particles may be oxidized by oxygen-rich bottom waters, converting carbon that was buried into dissolved carbon dioxide. At the same time, the physical mixing can expose fresh, easily degradable material to microbes, accelerating decomposition. Counterbalancing those effects, resuspension can also redistribute particles into settings where they are reburied more deeply, and it can stimulate phytoplankton blooms that temporarily draw down atmospheric carbon as the surface ocean feeds on newly released nutrients. The overall sign of the carbon balance depends on which of these processes dominates, and that is a matter of site-specific biology and geology.
For fisheries managers, the practical implication is that blanket bans on bottom trawling may not be the most efficient policy response. A more targeted approach, in which trawling is restricted or redirected away from carbon-rich muddy habitats while being allowed in areas of lower carbon density, could protect a large share of seabed carbon stocks without shutting down the entire industry. Several European Union member states are already piloting spatial planning tools that combine high-resolution maps of organic carbon stocks with vessel monitoring data from the fleet, creating a foundation for zoning that accounts for both fisheries and climate goals. Regulatory bodies such as the International Council for the Exploration of the Sea have been encouraging such approaches, and the new study reinforces the case by quantifying where the greatest carbon benefits lie.
The environmental stakes extend beyond carbon. Seabed disturbance also affects benthic biodiversity, habitat structure, and the productivity of fish stocks themselves. Corals, sponges, and long-lived bivalves are especially vulnerable because their growth is slow and their presence helps stabilize sediments. When these communities are damaged, recovery can take decades, and the associated loss of ecosystem services can cascade through the food web. Decision makers therefore face a multi-objective optimization problem in which carbon storage, fisheries yield, biodiversity conservation, and economic livelihoods all need to be balanced. The new work helps by converting a fuzzy qualitative concern into measurable quantities that can be plugged into planning models.
More research is needed before the findings can be translated into firm global guidance. Many regions lack detailed sediment carbon maps, and the response of different microbial communities to mechanical disturbance is still being characterized. Field experiments that compare trawled and untrawled plots over multi-year intervals are particularly valuable, and satellite remote sensing of surface chlorophyll responses to trawling plumes is emerging as a complementary observation tool. Fisheries scientists also caution that any trawling restriction must consider displacement effects, because closing one area can push fleets into others that may be equally sensitive. Still, the overall direction of travel is clear. Bottom fishing is neither uniformly harmless nor uniformly catastrophic for the climate. Its impact is a function of human choices about where gear goes, how often, and under what conditions, and careful management can substantially reduce the carbon cost of putting fish on the table.
Communication between fisheries scientists, sediment geochemists, and policy specialists is another area where new investment is needed. Historically, these communities have operated on separate research tracks, with fisheries biologists focused on stock assessments and sediment scientists focused on geochemical cycling. The recognition that bottom fishing can affect the global carbon budget creates a natural reason for them to collaborate, and international programs such as those coordinated through the Food and Agriculture Organization of the United Nations have started to support integrated projects. Bringing together the right expertise can accelerate the development of best practices that reduce environmental harm without undermining the economic viability of coastal fisheries communities that depend on well-managed seabeds.