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Different migratory tactics are suspected on the basis of laboratory experiments: Some individuals subjected to water reversal every 6.2 h swim only with the current, others only against the current, and some alternate swimming with and against the current at each water current reversal (Bolliet & Labonne, 2008 Bolliet, Lambert, Rives, & Bardonnet, 2007). The activity during the estuarine migration depends mainly on the tidal cycle, even if lunar and circadian rhythms and/or direct influence of light and tidal coefficient may also interact (Bolliet & Labonne, 2008 Bureau du Colombier, Bolliet, & Bardonnet, 2009). Then glass eels enter estuaries to grow and eventually colonize the freshwater network. They metamorphose into glass eels, probably as they reach the continental shelf. The European eel reproduces in the Sargasso Sea (Ginneken & Maes, 2005 McCleave et al., 1998 Schmidt, 1922), and after hatching, leptocephalus larvae use ocean currents (mainly the Gulf Stream) to migrate to the east Atlantic coasts of the northern hemisphere. japonica Temminck & Schlegel (Aida, Tsukamoto, & Yamauchi, 2003 Aoyama, 2009 Tesch, 2003). Interest in eels has been stimulated in recent decades by declines in recruitment in temperate species: the European Anguilla anguilla L., American A.
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