These ocean explorers have seen the damage done by industrial fishing. They want it to stop

Editor's note: Call to Earth is a CNN editorial series committed to reporting on the environmental challenges facing our planet, together with the solutions. Rolex’s Perpetual Planet Initiative has partnered with CNN to drive awareness and education around key sustainability issues and to inspire positive action.

(CNN) — The world’s oceans are under threat from rising sea temperatures, marine pollution and overfishing.

The effects are visible in shallow ecosystems suffering from coral bleaching, but less is known about the impact on deeper areas of the ocean such as the mesophotic or “twilight” zone, which lies between 30 and 150 meters (100 and 490 feet) below the surface.

This is the area that Ghislain Bardout and Emmanuelle Périé-Bardout, a husband-and-wife team of ocean explorers from France, are focused on. They founded Under the Pole, an organization that carries out diving expeditions to gather scientific knowledge on these extreme, uncharted environments, as part of the Rolex Perpetual Planet Initiative.

They have witnessed firsthand the impact of bottom trawling, a fishing method that involves dragging nets along the seabed to catch species that live close to the seafloor, such as cod, hake and shrimp. Around a quarter of all wild-caught seafood is caught via this method each year.

As the heavy nets scrape along the seafloor, they can collect unwanted bycatch and harm reefs and seagrasses, leading to the destruction of precious ecosystems. Despite this, the practice is permitted widely across the world, including in some marine protected areas (MPAs), such as in the French Mediterranean.

This year, the Bardouts carried out a series of expeditions in the Mediterranean Sea. As guest editors for CNN’s Call to Earth series, which reports on the environmental challenges facing our planet, together with the solutions, they spoke with CNN about the threats facing the mesophotic zone and what must be done to protect it.

The following interview has been edited for length and clarity.

CNN: What is bottom trawling and why is it so damaging to the ocean – specifically the mesophotic zone?

Emmanuelle Périé-Bardout: Bottom trawling is (a method of) fishing that you could compare to a bulldozer in a forest. If you imagine a forest which is being clear cut by a bulldozer, you can picture the danger for the biodiversity and the life inside the forest, and the same (happens) in the water with bottom trawling. But the problem of the ocean in general is that we don’t see it. You have bottom trawling everywhere, every day, and it’s a massive damage to biodiversity, but we just don’t see it.

CNN: When this damage happens how long does it take for corals to grow back? Can these ocean ecosystems recover from damage like that?

Ghislain Bardout: It can take hundreds of years to recover the ecosystem. It depends on the species, but most of them have very slow growth. For example, black corals, which are like underwater trees and can grow up to a meter and a half high, can be 200, 300, 400, 500, 600 years old. They can be destroyed in just a few seconds by a trawler. When they are destroyed, you lose the entire ecosystem very quickly – all the fish, all the shells, all the different species that create this ecosystem.

CNN: This summer you discovered a rich marine animal forest ecosystem in Fourni, Greece. Did you see signs of industrial fishing there?

Emmanuelle: The first time we dived to the marine animal forest we found in Fourni we saw the tracks of the bottom trawler just close to the forest.

Ghislain: This rich ecosystem is on some rocks with sand plains all around it. When trawling, the fishermen try to be as close as possible to this rich ecosystem, but they try not to go on it, because the rocks could damage the nets. But indirectly, fishing so close to those rich ecosystems is very damaging, because it’s not only physical destruction, it’s generating mud clouds that then fall on the ecosystem, and little by little, it destroys life. This is where the question of science is essential. It’s not only the fact that there are regulations banning trawling, but you also need to know where to do it, and this needs exploration, science and knowledge.

CNN: How does documenting these deep ecosystems help to secure their protection?

Ghislain: With regulations, if you don’t know what to protect and where to protect it, they have no value. You have to know where to apply those regulations. You need to have knowledge of those ecosystems: where are they, what species are living in this ecosystem, what are the conditions of those ecosystems, what are the threats to those ecosystems? If you have a good understanding of that, you can adapt the conservation issues to it. For instance, some species are very fragile and are highly threatened and need a very strong and total conservation, whereas other locations could be partially fished some of the year, but not during the spawning or reproduction period.

Emmanuelle: Without science-based information, you cannot change the regulation and the conservation policies. So it’s a tool, I would say. But also, we cannot wait to have all the science information to act and ask for better protected areas, because it can take years – and we don’t have years.

CNN: What existing protections are there for these deep ecosystems in the Mediterranean?

Emmanuelle: This year, Greece was the first European country to say that they will ban bottom trawling in their protected areas by 2030. It’s kind of a joke, to say “we will protect a marine protected area,” but it’s better than nothing. It was a first step, and England followed, saying they will ban bottom trawling in most of their marine protected areas. So it’s going in a good direction, but we are waiting for the United Nations Ocean Conference, which will take place in Nice, France, next June. I hope that more countries, including France, will move forward to ban bottom trawling in MPAs. I think we should quickly transition to a fishing technique that is more selective – and it exists, it’s small fishermen.

Ghislain: Local, selective, low-scale fishing with many small boats makes sense, and it also distributes the resource and the economy much better. Whereas industrial fishing is very concentrated on a few companies which are making a lot of profit based on the global resources of the oceans.

CNN: Besides bottom trawling, what other threats to the ocean’s mesophotic zone have you encountered during your research?

Ghislain: There is global warming, plastic pollution. The impact of global warming in the ocean can be huge, especially in shallow waters. As you may know, this year was a huge bleaching year. But where we worked in French Polynesia (in the South Pacific), our studies revealed that at a depth below 30 or 40 meters (98 or 131 feet) in the mesophotic zone, there was just a little bit of bleaching. The same occurs in the Mediterranean Sea with the gorgonias (sea fan corals): they have been destroyed in shallow waters by heatwaves in the last few years, whereas in the mesophotic, in Greece, or in France, they are sheltered.

That might change in the future, due to global warming, but for now they are protected, and that’s a huge hope. That should encourage us to act now, as the mesophotic could have a role as a refuge and be a regenerative ecosystem.

Emmanuelle: We are often asked about solutions and technology. I think it’s interesting to work on solutions. But if you have a fire in the forest, you won’t put seeds in until you’ve put the fire out. That’s what marine protected areas are for – they give us the time we need to stop the fire.

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