On 20 November, the R/V Dr Fridtjof Nansen departed Maputo, Mozambique, beginning a three-week multidisciplinary research cruise in the southwestern Indian Ocean under the 2024–2028 phase of the EAF-Nansen Programme. The survey represented a major regional initiative to improve scientific knowledge in support of sustainable fisheries management in the Southern Indian Ocean.
The cruise brought together 24 participants including scientists, technicians, and observers from 11 countries across the Southern Indian Ocean Fisheries Agreement (SIOFA) region, including Seychelles. Participants contributed expertise in fisheries acoustics, benthic ecology, oceanography, chemistry, and deepwater shark taxonomy. In addition to generating new scientific information, the cruise served as an important training platform, strengthening regional capacity through hands-on experience in modern survey methods.
The primary objectives of the survey were to improve acoustic knowledge of deep-sea fish resources, with particular emphasis on alfonsino; to document vulnerable marine ecosystems through benthic investigations; and to further develop tools for the accurate identification of deepwater sharks. These activities were designed to directly support SIOFA’s scientific advice and management responsibilities, particularly in areas beyond national jurisdiction.
Survey operations focused on a series of seamounts and underwater features south of Madagascar, including Capricorn, Banana, Walter’s Shoal, and Station X. The vessel employed scientific echosounders and multibeam systems to map seafloor bathymetry and detect fish aggregations. Acoustic observations were supported by pelagic and demersal trawling, CTD casts, sediment grabs, and targeted biological sampling.
Notable results were obtained at Walter’s Shoal, where fish schools were detected along the shallow caldera rim, and at Station X, one of the few sites suitable for both acoustic surveys and trawling. Here, aggregations of alfonsino were successfully investigated, providing valuable data for assessing the potential of non-intrusive acoustic methods for estimating biomass of deep-sea species.
Benthic surveys yielded new insights into poorly documented deep-sea habitats of the southern Indian Ocean. Baited Remote Underwater Video systems, combined with seabed mapping and sediment sampling, revealed diverse communities of corals, sponges, and associated fauna. Observations within SIOFA Benthic Protected Areas, where bottom fishing is prohibited, contributed directly to the identification of vulnerable marine ecosystems and informed spatial management measures aimed at minimizing impacts on sensitive habitats.
The cruise also advanced understanding of deepwater sharks in the region. Remote video systems recorded several rare and vulnerable species, some observed alive at depth for the first time. These observations were complemented by genetic sampling and the continued testing of a digital “smart” identification key developed through collaboration between SIOFA, the Common Oceans Deep-Sea Fisheries Project, and the Virginia Institute of Marine Science. Environmental DNA sampling further enhanced the survey, providing a non-invasive approach particularly suited to protected areas.
Life onboard the R/V Dr Fridtjof Nansen was demanding but highly collaborative. Scientific operations ran around the clock, with laboratories active day and night. The shared working environment fostered strong professional relationships across disciplines and nationalities, reinforcing the EAF-Nansen Programme’s core objectives of knowledge exchange and capacity development.
At the end of the survey, the vessel returned with a substantial body of data that will support SIOFA scientific advice, contribute to regional stock assessments, and improve understanding of deep-sea ecosystems in the Southern Indian Ocean. The cruise demonstrated the importance of international cooperation and multidisciplinary science in addressing knowledge gaps in remote marine environments. It reaffirmed a shared commitment to sustainable fisheries management and biodiversity conservation.
