The IUCN Congress in Abu Dhabi backed a motion urging extra caution for activities in the ocean's mesopelagic or "twilight" zone, which lies about 656–3,280 feet (200–1,000 m) below the surface. The zone may contain up to 90% of the ocean's fish biomass and plays an important role in transporting carbon to the deep sea, helping to regulate the climate. Delegates and conservation groups warn that pollution, intensified fishing, deep‑sea mining and ocean deoxygenation put this fragile ecosystem at risk, while some governments and industry push for expanded resource exploration. Advocates hope the IUCN decision will spur protective policies in other international forums.
IUCN Urges Caution for the Ocean's 'Twilight Zone' as Industry Eyes Mesopelagic Resources
The IUCN Congress in Abu Dhabi backed a motion urging extra caution for activities in the ocean's mesopelagic or "twilight" zone, which lies about 656–3,280 feet (200–1,000 m) below the surface. The zone may contain up to 90% of the ocean's fish biomass and plays an important role in transporting carbon to the deep sea, helping to regulate the climate. Delegates and conservation groups warn that pollution, intensified fishing, deep‑sea mining and ocean deoxygenation put this fragile ecosystem at risk, while some governments and industry push for expanded resource exploration. Advocates hope the IUCN decision will spur protective policies in other international forums.
10:20, 07.11.2025Environment
IUCN pushes for stronger protections in the ocean's mesopelagic 'twilight zone'
Delegates at the International Union for Conservation of Nature (IUCN) Congress in Abu Dhabi voted in favour of measures calling for heightened scrutiny of new commercial activities in the ocean's mesopelagic, or "twilight," zone. Conservationists say the resolution is meant to ensure extra caution when approving future fishing, geoengineering and deep‑sea mining proposals that could harm a fragile and globally important ecosystem.
What and where is the mesopelagic? The mesopelagic layer lies roughly 656 to 3,280 feet below the surface (about 200–1,000 metres). Sunlight is weak there and pressure rises with depth, creating a distinct environment that supports a rich and unusual community of life.
Scientists estimate that up to 90% of the ocean's fish biomass may live in or transit through this zone, including fish, crustaceans and cephalopods. Many of these animals perform daily vertical migrations: they rise toward the surface to feed at night and return to depth by day, transporting carbon into the deep ocean and helping regulate Earth’s climate.
“We see great potential in the mesopelagic part of the ocean,” said Esben Sverdrup-Jensen, president of the European Association of Fish Producers Organisations. “Seventy‑two percent of the 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.”
That potential, however, comes with risk. The mesopelagic is increasingly exposed to pollution and escalating industrial pressures, including intensified fishing and proposals for deep‑sea mining. Many species in this zone reproduce slowly and the layer plays a key role in carbon sequestration, making it particularly vulnerable to stressors such as ocean deoxygenation and warming.
Policy tensions are rising. In April, the U.S. administration issued an executive order calling for sustained national leadership in deep‑sea science, seabed mineral resources and related technology, encouraging exploration and development of critical minerals in marine environments. Industry advocates see economic opportunities, while conservation groups warn of long‑term ecological costs.
Chris Dorsett, vice president of Ocean Conservancy, told Mongabay that the IUCN motion is “a great step in raising awareness” of the mesopelagic's importance. “Our hope is catalyzing action in other fora to implement on‑the‑water protections,” he said, noting that the IUCN often incubates policy ideas that later influence international processes.
Why this matters: Decisions made now about fishing, mining and geoengineering in the mesopelagic will affect biodiversity, carbon cycling and coastal communities. Advocates are calling for precautionary, science‑based policies to avoid irreversible damage to a little‑understood but globally significant part of the ocean.