International eel symposium, 2003 - Quebec August 11, 2003
Oral Presentation

Triggers and Phenomenon of Watershed Colonization by European Glass Eels and Elvers: State of the Art and New Approaches

Edeline, E.* Cemagref, Unité R..A.C., 50 avenue de Verdun, 33612 Cestas cedex, France, eric.edeline@bordeaux.cemagref.fr
Dufour, S. M.N.H.N., Laboratoire de Physiologie, 7 rue Cuvier, 75231 Paris cedex 05, France
Elie, P. Cemagref, Unité R..A.C., 50 avenue de Verdun, 33612 Cestas cedex, France

Presenter email address: eric.edeline AT bordeaux.cemagref.fr

Abstract Text: Within the tidal area of the catchments, upstream migration is only possible for elvers using selective tidal stream transport. Many environmental factors can influence this migratory behavior. At the tidal limit, elvers must switch from the selective tidal stream transport to a strictly countercurrent swimming behavior. Many individuals can be caught in the estuary swimming in the water column during ebb tide, possibly because they do not exhibit a rhythm of activity in phase with the tidal flow. These individuals probably never reach the tidal limit, at least at the elver stage. Moreover, Sr/Ca otolith studies in yellow and silver eels show that some individuals stop their migration in the estuary or in marine habitats. We assume that the divergent migratory patterns at the elver stage are the result of inter-individual differences of activity rate and ebb and flood tide rhythm of this activity. Thus, the colonization would not be only environmentally conditioned, but controlled by the interaction of external and internal factors. After a review of the knowledge about the watershed colonization by elvers, possible approaches to describe these internal factors are discussed, with special focus on the tidal limit area and thyroid hormones.