ICES CM 2004/ S:20 Not to be cited without prior reference to the authors Assessment of upstream migration and reproductive behaviour of allis shad (Alosa alosa (L.)) from a small river of the Atlantic coastal zone (L’Aulne, Brittany, France). M.L. Acolas, V. Véron, H. Jourdan, M.L. Bégout Anras, M.R. Sabatié, J.L. Baglinière. Adult allis shad (Alosa alosa (L.)) behaviour was analysed during the last part of upstream migration in River Aulne and during reproduction on a unique spawning ground downstream of an insurmountable dam. Population-level migration and reproduction were studied by counting the number of migrating fish and the number of night acts of spawning since 2000. The influence of environmental conditions (water discharge and temperature) was highlighted. We discuss yearly characterisation of the migration and reproduction activities during the all spawning season based on the number and the sex ratio of migrating shad and on the direct counting of spawning acts. Keywords: Allis shad, behavioural ecology, anadromous migration, reproduction. M.L. Acolas, J.L. Baglinière, H. Jourdan, M.R. Sabatié : UMR INRA-Agrocampus Ecobiologie et Qualité des Hydrosystèmes Continentaux, 65 rue de Saint Brieuc, CS 84215, F-35042 Rennes Cedex, France [tel : 02 23 48 54 41, fax : 02 23 48 54 40, e-mail :
[email protected],
[email protected]]. V. Véron : Institut d’aménagement de la Vilaine, Boulevard de Bretagne, BP 11 56130 La Roche- Bernard, France, [
[email protected]]. M.L. Bégout Anras : Centre de Recherche sur les Ecosystèmes Marins et Aquacoles – UMR CNRS/Ifremer - B.P.