Recent research highlights the complex migration of European eel larvae, which face substantial challenges as they make their way from the Atlantic Ocean through the Strait of Gibraltar to the Mediterranean Sea. Observed during a 2022 study aboard the German Research Vessel Meteor, the transport mechanisms influencing these larvae are finally coming to light.
The European eel (Anguilla anguilla), currently rated as critically endangered by the IUCN, has experienced significant population declines. While monitoring efforts focus on glass eels and yellow eels along European coasts, the early life stages have remained poorly understood, especially the distance they travel and the environmental factors affecting them.
This study aimed to fill the knowledge gap by monitoring the movement and distribution of eel larvae within the unique hydrographic conditions of the Strait of Gibraltar. The results indicate how the interplay between ocean currents, tides, and the larvae’s behavioral adaptations to vertical migration makes successful transport to the Mediterranean dependent on specific conditions.
During the 24-hour observation, researchers employed acoustic Doppler current profilers to measure water velocities and sampling equipment to catch larvae. Initial findings showed no larvae captured during daytime sampling, but nighttime hauls produced significant catches, indicating their active movement during these periods.
Notably, 31 leptocephalus larvae were collected, including 17 European eels. The study demonstrated clear patterns, showing high catch numbers related to the eastward-moving currents, particularly after sunset, aligning with the larvae’s ascent to surface layers.
The research emphasizes the importance of strong eastward surface currents at nighttime, which may facilitate the larvae’s migratory success during their transoceanic journeys. Just as the larvae adapt their behaviors, the tides and current dynamics of the Strait present unique challenges and opportunities for their recruitment.
Understanding these mechanisms is not only significant for the biology of the European eel but could also guide conservation strategies. With currents and environmental conditions constantly fluctuated, the study paves the way for targeted monitoring efforts to effectively track eel recruitment trends across the Mediterranean.
The findings not only add to the body of knowledge about European eels but also suggest potential measures to mitigate the impacts of changing oceanic conditions and human activities threatening this remarkable species.