What is bottom trawling? How it works and environmental impact

What is the environmental impact of bottom trawling? And how is it linked to the biodiversity crisis and climate change?

Bottom trawling emits as much CO2 as the aviation industry

While it's responsible for the largest share of global catch compared to any other fishing methods, bottom trawling is notorious for its destructive environmental impact on the most delicate marine habitats. The heavy nets drag on the seabed to catch marine species that live there. In doing so, they harm reefs and clear-cut seagrasses, one of the ecosystems that absorbs the most carbon - 35 times faster than tropical rainforests do. By destroying seagrass meadows, bottom trawling releases as much CO2 as the entire aviation industry.

Among the top 10 countries in the world that emit the most carbon emissions through bottom trawling, 8 are in Europe: UK, Italy, Denmark, France, the Netherlands, Norway, Croatia and Spain.

Bottom trawls are also unselective in what species they fish. That means that they unintentionally capture a lot of non-target species, which can make up to 60% of the total catches. Unwanted fish and endangered animals such as dolphins, sea turtles, and sharks, get stuck in the nets, get badly injured or killed, and are then thrown back to the sea.

By damaging seafloor ecosystems and harming marine life with bottom trawls, the fishing industry is effectively removing one of the most important natural mitigation tools we have against the climate crisis, while contributing to a decline in biodiversity.

Is bottom trawling banned in Europe?

The ban on bottom trawling in many areas of European Union (EU) waters goes back to 2006, when the EU adopted a regulation to ban fishing practices that are likely to damage marine habitats. It specifically bans bottom trawling, pelagic trawling, purse seining and dredging in all marine protected areas (MPAs) that host certain vulnerable habitats such as seagrass meadows and coral reefs.

The European Commission itself defined bottom trawling as one of "the most widespread and damaging activities to the seabed and its associated habitats” and advocated for a transformation of the fishing industry to reduce its impact on the environment.

With just 0.23% of the Mediterranean fully or highly protected, its marine ecosystems are in serious trouble. This makes the European Commission's call to ban bottom trawling all MPAs by 2030 even more important.

But this bottom trawling ban has not yet turned the tide for marine conservation, almost 20 years after its entry into force. That is because some EU countries don’t play by the rules and still refuse to implement it.

Meanwhile, there are also good news: trawlers are effectively banned from fishing in deep-sea areas around the Canary Islands, Azores and Madeira, as well as some parts of the Baltic Sea and the Mediterranean that host fragile habitats and vulnerable marine species.

In April 2024, Greece set an example in terms of safeguarding MPAs by announcing a ban on bottom trawling in all its marine protected areas by 2030.

How ClientEarth is using the law to put an end to illegal bottom trawling

In the Mediterranean, France currently allows bottom trawling in its so-called ‘protected’ marine areas. In May 2024, BLOOM and ClientEarth, who are members of the Med Sea Alliance, have requested action from the French authorities to ensure that they finally comply with EU law.

According to our legal expert Nils Courcy: “The simple fact that France is allowing trawlers to fish in protected areas that should be closed to trawling is a scandal. The European legal framework is not being respected. France's interpretation of it is contrary to the letter and spirit of the law and tramples the major European environmental principles.”

We are demanding that France revises three decrees authorising bottom trawling in certain French MPAs where it should be banned. We will not hesitate to go to court should the administration fail to respond favourably to this request.

We are also advocating for stronger fisheries control systems and regulations on fish imports. This will help to ensure the seafood in Europe is sourced responsibly without harming human rights or the environment. We also urge the rapid implementation of CATCH, the EU-wide digital system that makes seafood fully traceable.

What are the sustainable alternatives to bottom trawling?

Fishing more sustainably is possible and alternatives to bottom trawling do exist: adopting different and more sustainable fishing gear, or using artisanal, small-scale fishing techniques that are more selective and less energy intensive. These are only a few examples of how we could reduce unwanted by-catch and slow down the depletion of our seas and oceans, while also reducing climate emissions.

Restoring oceans is not only important for safeguarding marine life. It is also urgently needed if we want to tackle global hunger and food security. As a matter of fact, MPAs can help fish come back, replenish fish stock and boost seafood catch to eight million tonnes.