Details on the transport of European eel larvae through the Strait of Gibraltar into the Mediterranean Sea.

Numbers of European glass eels (Anguilla anguilla) monitored along the Atlantic and Mediterranean coasts of Europe currently serve as the main stock indicator in assessment of this critically endangered species. Spawning, however, takes place exclusively in the Sargasso Sea, several thousand kilometers away. The beginning of its complex lifecycle is characterized by a distant and lengthy larval drift, before the young-of-the-year reach the monitoring stations at the European coasts. The oceanic mechanisms regulating dispersal and distribution of European eel leptocephalus larvae, before they metamorphose into glass eels and colonize future growth habitats, are still poorly understood and data are scarce. Here, we present oceanographic and leptocephalus catch data from a 24-h station on board of the German Research Vessel Meteor, covering one event cycle of the tide-derived change of hydrographic conditions in the central part of the Strait of Gibraltar. Results of this study provide detailed insights on how the exchange of water masses between the Atlantic and the Mediterranean Sea may favor or prevent transport and migration of eel larvae through the Strait, which potentially plays a decisive role in timing and magnitude of larval recruitment events into the entire Mediterranean region.