The expedition is led by Professor Reinhold Hanel of the Thünen Institute of Fisheries Ecology (Germany), who has been working with his team in the Sargasso Sea region for more than a decade. His first research expedition to the area dates back to 2011, when scientists set out from Bermuda to investigate the spawning grounds of European eels—an event also reported locally at the time (https://www.royalgazette.com/environment/news/article/20110316/researchers-head-to-the-sargasso-sea-to-study-eels/).
Since then, the research has developed into a long-term survey programme. The current expedition, which concluded on April 12, 2026, represents the sixth survey of the working group in the Sargasso Sea since 2011, and the fifth mission conducted aboard the research vessel Walther Herwig III as part of a regular three-year survey cycle.
The Sargasso Sea is the only spawning area for the critically endangered European eel (Anguilla anguilla). The eels spawn in the ocean to the South of Bermuda but migrate several thousand kilometres to inshore Europe, the Baltic, the Mediterranean, and northern Africa, to live most of their lives in brackish or freshwater environments.
The eels are harvested for human consumption, driving a decline that is exacerbated by other threats, including habitat loss, barriers to migration, pollution, and more. The European eel has experienced more than 90% fall in recruitment since the 1970s.
“Many aspects of the eels’ spawning behaviour and early development remain unknown, including the exact locations and environmental conditions of spawning,”
explained Prof. Reinhold Hanel, Cruise Leader.
“During the recent expedition, researchers collected plankton samples across a large survey area in the western and central Sargasso Sea to determine the distribution, abundance, and size of eel larvae.”
“These data are essential for understanding recruitment processes and long-term population trends of this critically endangered species.
“The work also contributes to broader ecosystem research as, in addition to eel larvae, the scientists are studying plankton communities including jellyfish, sunfish larva and mesopelagic fishes that inhabit the so-called 'twilight zone' of the ocean.”
Prof. Hanel has been collaborating with the Sargasso Sea Commission for several years and has contributed to scientific initiatives supporting its conservation goals.
“A single species action plan for the European eel was agreed at the 15th Conference of the Parties of the Convention on Migratory Species in April 2026,”
said Dr David Freestone, Executive Secretary of the Sargasso Sea Commission.
“This plan has been in the making for years, with the Sargasso Sea Commission facilitating meetings of the range states of the European eel. Data from researchers like Prof. Hanel was instrumental in getting it over the finish line.”
Bermuda is the only land mass in the Sargasso Sea, and the Bermuda Government has championed the conservation of this globally significant and unique ecosystem for more than a decade.
The Sargasso Sea Commission was established with the signing of the Hamilton Declaration in Bermuda in 2014 with the aim to “encourage and facilitate voluntary collaboration toward the conservation of the Sargasso Sea.”
The Governments of Bermuda and the UK have recently launched a new initiative – the development of a ‘Hamilton Declaration II.’ The aim of the new declaration is to provide a mechanism to signal political support for the development of a collective proposal for an area-based management tool for the conservation of the Sargasso Sea under the BBNJ agreement.
The research vessel Walther Herwig III operated in the Sargasso Sea for four weeks before returning to Bermuda. Further insights into the work on board can be found in the institute’s cruise blog: https://www.thuenen.de/en/topics/seas/no-fisheries-research-without-research-vessels/sea-blogs/walther-herwig-iii-cruise-498
Words by Fae Sapsford.
About the Sargasso Sea Commission
The Global Environment Facility-funded Common Oceans Program Sargasso Sea project (GEF-UNDP-IOC-SSC) is committed to facilitating a collaborative, cross-sectoral, and sustainable stewardship mechanism to establish a comprehensive conservation framework to protect the unique ecosystem of the Sargasso Sea. Led by UNDP, implemented by IOC UNESCO, and supported by an extensive network of partners, it brings together the regional fisheries management organisations, other UN-mandated bodies, national agencies, intergovernmental organisations and initiatives, the private sector, civil society and academia.
In addition to the GEF-UNDP-IOC-SSC project, the Sargasso Sea Commission is supported by a sister project. Funded by the French Facility for Global Environment, and in partnership with the University of Western Brittany, Mar Viva, and the Sargasso Sea Commission, the ‘SARGADOM’ project focuses on two remarkable high seas sites – the Sargasso Sea in the North Atlantic (‘SARGA’) and the Thermal Dome in the Eastern Tropical Pacific (‘DOM’). The project aims to contribute to the protection of biodiversity and ecosystem services and to facilitate the development of hybrid ocean governance approaches for the two sites.
For more information, please contact Fae Sapsford – fsapsford@sargassoseacommission.org