Abstract

A study was carried out on the brown trout population of the Oir River (Normandy, France) to understand the relation between juvenile growth and migratory behaviour (i.e. localisation of the growing environment). Thus 5894 0+ brown trout have been PIT-tagged from 1995 to 1999 and monitored using flat bed antennae, permanent trapping and electrofishing to interpret fish movements at a fine spatial and temporal scale as well as growth performances. Data have been analysed to group individuals according to life history traits, including juvenile growth, sex and migration processes in freshwater and to the sea. Results showed that migratory behaviour is variable among year classes and that juvenile growth rates during first and second years play important but different roles on migration determinism.