Duration: 23 February to 30 April 2026

Cruise area: Atlantic

Purpose: Research into the early life stages of the European eel in the central Sargasso Sea

The distribution and abundance of early developmental stages of the European eel (Anguilla anguilla) are to be investigated in the central Sargasso Sea. The study will use a time series to draw conclusions about the long-term effects of changing hydrographic conditions on the distribution, abundance and survival of eel larvae in the Sargasso Sea. In the medium term, the data series will provide the information necessary for the success of the measures introduced to restore the eel population. In addition, the frequency of occurrence and distribution of other fish larvae and gelatinous zooplankton will also be investigated in order to gain insights into possible changes in the larval community in the Sargasso Sea.

An Isaacs-Kidd Midwater Trawl (IKMT) will be used for the investigations. In addition, a further development of this net will be used, which, in combination with a multi-net midi (HydroBios), will enable depth-stratified sampling. This will allow the depth distribution of the larvae and time-of-day-dependent changes in their depth of residence to be recorded. This should lead to a better understanding of the ecology of the early life stages of eels and may also improve the data basis for modelling the drift of eel larvae.

In addition, the species community in drifting brown algae of the genus Sargassum will be investigated. Brown algae will be collected using a sink net, a cast net or the work/rescue boat. The use of a large-mesh IKMT (4 mm) will also provide samples of macrozooplankton and mesopelagic fish for accompanying investigations.

The research expedition is not intended to be a stand-alone project. It is part of a series of Sargasso Sea research expeditions that began in 2011, which regularly record the distribution of eel larvae and the hydrographic conditions in the spawning grounds during the presumed main spawning season and are intended to provide basic data for the stock development of the European eel.

In addition to staff from the Thünen Institute, scientists from the Swedish University of Agricultural Sciences, Wageningen University, Charles University in Prague, Uppsala University and the Centre National de la Recherche Scientifique in Toulouse will complete the research team.