Patterns of silver eel (Anguilla anguilla L.) sex ratio in a catchment

Pascal Laffaille (1) , Anthony Acou (1) , Jérôme Guillouët (2) , Béatrice Mounaix (2) , Antoine Legault (2)

1 Biodiversité fonctionnelle et gestion des territoires
2 Fish Pass

Changes in the numbers and size-class structure of European silver eels, Anguilla anguilla, in the River Fre'mur (France) were examined over a 9-year period after installation of downstream eel passes. The number of silver eels migrating downstream peaked in 1999, then decreased strongly and steadily after 2000, reaching relatively low levels. At the same time, a gradual shift in the silver eel sex ratio from a dominance of males (size from 270 to 442 mm, age from 3 to 6 years) to females (size from 366 to 1112 mm, age from 4 to 9 years) was recorded. Possible explanations for the escapement patterns observed are environmental sex determination and the installation of eel passes on the main hydraulic engineering structures in 1992 and 1996.

Mots clés: European eel; Downstream migration; Sex ratio; Eel passes; Environmental sex determination

Domaines: Biodiversité; Ecosystèmes

Pascal Laffaille, Anthony Acou, Jérôme Guillouët, Béatrice Mounaix, Antoine Legault. Patterns of silver eel (Anguilla anguilla L.) sex ratio in a catchment. Ecology of Freshwater, 2006, 15, pp. 583-588. ⟨10.1111/j.1600-0633.2006.00195.x⟩. ⟨hal-00793405⟩