Global conservation body takes first step to protect ocean’s twilight zone

The mesopelagic zone is the chilly, dimly lit layer of ocean found 200-1,000 meters (660-3,300 feet) below the surface, which scientists say plays key roles in the marine food web and carbon cycle. On Oct. 15, delegates to the IUCN World Conservation Congress in Abu Dhabi adopted a motion to protect it. The motion calls for any activities that could harm the mesopelagic ecosystem, including fishing, geoengineering and deep-sea mining, to be approached with caution and guided by the best available science.

The World Conservation Congress is a global forum focused on nature and conservation that takes place every four years. The motion is one of the first steps toward safeguarding the mesopelagic zone globally, although it is focused more on limiting future damage rather than repairing any harm already inflicted on this part of the ocean.

The mesopelagic zone, sometimes called the “twilight zone,” is home to an immense biomass of fish — 600 million metric tons, according to one estimate. Species inhabiting this zone include lanternfish, pearlsides and squid, which are crucial food sources for predators like dolphins, tunas, marlins and sharks. Research suggests this vast zone also plays an essential role in regulating the climate by facilitating a process called the “biological pump” that moves carbon from the atmosphere into the deep ocean for long-term storage.

For now, a commercial mesopelagic fishing industry remains largely speculative. Launching it would require overcoming difficulties in locating, catching and processing mesopelagic fish. Still, there’s considerable enthusiasm for finding a way to make it work. While mesopelagic fish have been pursued for possible human consumption, there is a particular interest now in harvesting them for fertilizers or aquaculture feed.

Until now, efforts to protect the ocean’s twilight zone have been limited. The United States enacted protections for certain mesopelagic fish off its West Coast in 2016, and East Coast in 2017, but few other countries have taken comparable action. In contrast, nations like Norway and Iceland have run trial mesopelagic fisheries in recent years, and the European Union (EU) has invested about $17 million in research programs to assess the feasibility of fishing in the twilight zone.

The new IUCN motion not only calls for the protection of mesopelagic ecosystems, but for taking a precautionary approach to potentially harmful activities, such as fishing, deep-sea mining and geoengineering — none of which have yet started on a commercial level. For instance, it calls for these activities to be regulated and assessed based on a scientific understanding of mesopelagic communities, any unregulated or adversely impactful activities to be stopped and regular reporting of catch and bycatch levels. It also calls for the use of management measures, such as marine protected areas, to protect the structure and function of mesopelagic communities; for collaborative research, monitoring and strategic environmental assessments; and for policymakers to champion the “importance of mesopelagic communities in climate change policies and actions.” Last but not least, it calls for the IUCN to support and promote these actions.

What this motion does not call for is an outright pause or block on any and all activities that might impact this ocean zone, unlike other IUCN motions, such as one passed at the 2021 World Conservation Congress that called for a moratorium on deep-sea mining.

Chris Dorsett, vice president of conservation at the Washington, D.C.-based NGO Ocean Conservancy, whose organization and two other U.S. NGOs helped draft the motion, said that while the vote is nonbinding, it represents a “great step in raising awareness” about the mesopelagic ecosystem and the need to protect it.

“Our hope is catalyzing action in other fora to implement on-the-water protections,” said Dorsett, who spoke to Mongabay while attending the congress. “The IUCN has often been an incubator for policy ideas that then get legs and move into implementation in other processes.”

Dorsett added that future protections for the mesopelagic zone could emerge via national legislation within individual countries’ exclusive economic zones, or through regional fishery management organizations in international waters. He said the motion’s adoption at this time was “exciting” since it followed the ratification of the Biodiversity Beyond National Jurisdiction (BBNJ) treaty, also known as the high seas treaty, on Sept. 19, which he said could bolster future protection of the twilight zone.

“What the BBNJ treaty does is put some good tools in the toolbox, like environmental impact assessments for proposed activities, as well as the ability to implement area-based protections,” Dorsett said. “Our hope is that these tools can be used to address existing management gaps.”

The motion passed with 713 votes in favor from governments, NGOs and Indigenous groups, and 46 votes against. Sonsoles San Román, an IUCN communications officer, told Mongabay via email that the IUCN would “not provide country breakdowns or details of what IUCN Members voted individually.”

Some members of the fishing community appeared to express support for the motion while also promoting a view of mesopelagics as a resource, if fished sustainably. For instance, Caitlyn Czajkowski, executive director of the National Aquaculture Association, a U.S. trade association, told Mongabay in an emailed statement that the organization “respects the IUCN’s recent motion” and supports “the responsible management of natural resources, both in aquaculture and wild capture fisheries.” Czajkowski also said her association would ultimately “defer to those national and international fishery management bodies to evaluate and regulate mesopelagic fishing activities, in alignment with scientific and sustainable management principles.”

Esben Sverdrup-Jensen, president of the European Association of Fish Producers Organisations, which promotes sustainable fishing and policy development in Europe, described the mesopelagic zone’s significance for the industry and emphasized the need for its sustainable management, when Mongabay asked for his reaction to the IUCN motion. “We see great potential in the mesopelagic part of the ocean,” Sverdrup-Jensen told Mongabay in an emailed statement. “72% of earth is covered in water yet less than 10% of our food comes from the oceans. If the mesopelagic biomass is sustainably managed, the potential of this resource is limitless.”

For Dorsett, the IUCN motion represents a strong first step to protecting the twilight zone, even if it doesn’t detail how fishing or other activities might ultimately be conducted there.

“Let’s look before we leap,” Dorsett said, “because the mesopelagic zone is just too important from a biodiversity, climate regulation and ecosystem functioning perspective.”

Banner image: A diamond squid, which is found in both epipelagic and mesopelagic zones. Image by Mike Bartick / Ocean Image Bank.

Elizabeth Claire Alberts is a senior staff writer for Mongabay and was recently a fellow with the Pulitzer Center’s Ocean Reporting Network. Find her on Bluesky and LinkedIn.

Twilight zone fishing: Can we fish the ocean’s mesopelagic layer?

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