New clues on the Atlantic eels spawning behavior and area: the Mid-Atlantic Ridge hypothesis

Yu-Lin K. Chang,Katsumi Tsukamoto,Yasumasa Miyazawa,Eric Feunteun

doi:10.1038/s41598-020-72916-5

Abstract

The Sargasso Sea has long been considered as the only spawning area for Atlantic eels, despite the absence of direct observations. The present study raises a novel scenario, deviating from Schmidt’s dogma, begins with a review of historical and recent observations that were combined to build up a global theory on spawning ecology and migration behavior of Atlantic eels. From this, it is argued that a favorable spawning area could be located eastward of Sargasso Sea at the intersection between the Mid-Atlantic Ridge and the oceanic fronts. Ocean circulation models combined with 3D particle-tracking method confirmed that spawning at this specific area would result in larval distribution fitting the field observation. This study explores the hypothesis that leptocephali are able to swim and orientate to reach their specific growth areas. It proposes a novel framework about spawning ecology, based on orientation, navigation and meeting cues of silver eels to the spawning area. Together this framework may serve as a stepping-stone for solving the long-lasting mystery of eel reproduction which first came out 2,400 years ago and promotes the understanding of oceanic migration and reproduction of marine organisms.

Highlights

The Sargasso Sea has long been considered as the only spawning area for Atlantic eels, despite the absence of direct observations
After many research cruises collecting transparent leaf-like eel larvae known as leptocephali, Schmidt proposed a theory that eels in the Atlantic Ocean were born in the Sargasso Sea and transported by currents to the Caribbean Sea and North American coastal waters in the case of American eels, and to the Mediterranean Sea and European coasts in the case of European eels
Eels are thought to imprint a magnetic map on their first transoceanic migration from the spawning areas to the coasts[21]

Summary

Arguments and discussion

To enable successful spawning of Atlantic eels in remote offshore areas of the ocean, three conditions need to be met. Our numerical simulation showed that a different departure point (spawning area), located above the Mid-Atlantic Ridge, resulted in a distribution of leptocephali larvae similar to historical observations in the Atlantic Ocean These results strongly suggest that oceanographic surveys should be organized outside the Sargasso Sea, in the vicinity of the Mid Atlantic Ridge. V-larvae released near the salinity front showed quick dispersion westward, entering the Caribbean Sea and the Gulf of Mexico with some going to the Gulf Stream This pattern is similar to that of Japanese eels in the Pacific Ocean that established their migration loop in the southwest corner of the subtropical gyre using the NEC and the K uroshio[42] (Fig. 6). The first step in this process is to organize research cruises to enlarge the domain of survey and to validate a newly proposed Mid-Atlantic ridge hypothesis

Methods

Findings

Additional information