Research vessel Dr. Fridtjof Nansen unveils the secrets of the Indian Ocean’s international waters

The UN-flagged research vessel R/V Dr. Fridtjof Nansen has completed a landmark scientific mission to the high seas of the southwest Indian Ocean, shedding new light on mysterious deep-sea ecosystems and strengthening the science needed for sustainable ocean management.

Twenty scientists from 11 countries mapped underwater landscapes and vulnerable marine ecosystems, identified little known deep-sea shark species, and studied seabirds and marine mammals. Each area of study was chosen to support responsible fisheries management and map impacts on fragile deep‑sea habitats.

Organized by FAO’s Common Oceans Deep‑Sea Fisheries Project, the FAO EAF‑Nansen Programme and its partner the Institute of Marine Research (IMR), and Norway, the three-week expedition wrapped up just before the Biodiversity Beyond National Jurisdiction Agreement (BBNJ) entered into force, calling for robust data to guide conservation and sustainable use of marine biodiversity in international waters.

Five years in the making, the research cruise was a collaborative feat, partnering also with the Southern Indian Ocean Fisheries Agreement (SIOFA), responsible for managing non-tuna fisheries in the high seas of the region.

“This work provides the science behind management measures,” said Common Oceans Program Coordinator Viktoria Varga Lencses: “If we want effective ocean governance, decisions must be grounded in robust, transparent, and collaborative science. This expedition was designed to meet this moment.”

RV Dr Fridtjof Nansen (Maputo) ©FAO/Anthony Thompson

Videoing ocean depths ©FAO/Anthony Thompson

The hidden world of deep-sea sharks

Scientists used baited remote video systems on the sea floor to spot deep‑sea shark species rarely seen alive. Among them were CITES-listed vulnerable gulper sharks and several other species, susceptible to impacts from fishing gears. They captured the first‑ever video of a live Dark Mouth Chimaera - a creature only seen before from two dead samples. They also filmed lantern sharks swimming in their natural deep‑sea habitat for the first time.

Researchers collected environmental DNA (eDNA), genetic material floating in the water, to help determine which species were present, even in protected areas, without the need to catch them. They also trialed a new “smart” shark identification key which will help observers identify species more accurately.  

The combined genetic information, video footage and physical samples provide the most complete set of data ever gathered to help assess deep‑sea shark populations in the Southwestern Indian Ocean high seas region.

“We’re only beginning to understand how many species are out there, and how they use these deep‑sea habitats,” said Anthony Thompson, FAO Deep‑sea Fisheries Expert and co‑cruise leader. “The more we know, the better we can protect sharks. Every new piece of information strengthens the scientific foundation needed to manage these vulnerable species responsibly.”

Filming rig on deck ©FAO/Anthony Thompson

Lantern shark ©FAO/Anthony Thompson

The deepest dwelling known shark species, the Portuguese dogfish (Centroscymnus coelolepis) ©FAO/Anthony Thompson

The ultra rare Dark Mouth Chimaera (Chimaera buccanigella) barely known by science ©FAO/Anthony Thompson

Mapping seafloor landscapes

Using high-resolution echo-sounding, the team produced detailed maps of the seafloor, from 30 meters to more than a kilometer deep. These showed underwater features like ridges, slopes, and underwater mountains, hosting deep-sea ecosystems. They also found fragile patches of coral and sponge, ecologically important and vulnerable to fishing gear used on the sea floor. Their efforts provide data crucial for the design of effective conservation measures.

“During this voyage we studied 3,400 nautical miles across remote seamounts south of Madagascar, using active acoustics to map the seafloor and observe fish aggregations linked to underwater mountains,” said Bjørn Erik Axelsen, IMR scientist and cruise leader of the scientific survey. “These methods allowed us to collect high-resolution bathymetry and new insights into both habitats and key species such as alfonsino.”

Insights from surface to seabed

Among the most striking findings were shallow‑water coral reefs thriving on the slopes of an underwater volcanic seamount just 30 meters below the surface - an unexpected oasis in the heart of the Indian Ocean. The team also observed vast, untouched deep‑sea habitats, offering a rare glimpse into ecosystems that have remained almost entirely beyond human reach. Adding to the picture, they recovered remnants of ancient coral reefs, possibly dating back thousands of years. 

Coral reef on Walters Shoal ©FAO/Anthony Thompson

Plotting the ocean depths with acoustics Walters Shoal ©FAO/Anthony Thompson

Life above the waves

As the ship traveled between research sites, scientists logged sightings of seabirds and marine mammals, from surfacing whales to wandering albatrosses with wingspans reaching 3.7 meters. At times, more than 30 of these giant birds circled the vessel. The observation work doubled as invaluable hands‑on field training for some of the team.

Science supporting sustainable management

The data collected during the voyage, from shark specimens to maps of the sea floor, will inform management strategies, support the work of the FAO’s EAF-Nansen Programme and Common Oceans Deep‑Sea Fisheries Project, and contribute to global biodiversity initiatives.

Reflecting on the mission’s broader impact, EAF-Nansen Programme Coordinator Merete Tandstad said: “This was more than a scientific expedition. It was a true collaborative effort to build knowledge, strengthen capacity, and deepen the partnerships we need for effective ocean governance.”

As the high seas remain among the planet’s least understood regions, the work of the international scientists and crew aboard the R/V Dr. Fridtjof Nansen advances our knowledge of this domain and strengthens foundations for its sustainable management.

“This was not simply a research cruise,” SIOFA Science Officer and acoustics co-team leader Marco Milardi said. “It was a vital investment in collecting invaluable data to support SIOFA’s mission of managing fisheries sustainably through science-based, ecosystem-informed decisions.”

To learn more about this initiative:

https://www.fao.org/in-action/commonoceans/what-we-do/deep-sea-fisheries/en

https://www.fao.org/in-action/eaf-nansen/en

https://www.fao.org/interactive/2025/eaf-nansen-sustainable-fisheries-research/en/

Factsheet on fisheries and the BBNJ Agreement

'Get to know the ocean and understand it' | GEF