Estimating movement and effective dispersal in a partially migratory fish
Résumé
Population genetics can be useful to understand the role of biological factors that impact population functioning. Due to their phenotypic plasticity and life history variability, population structure of partial anadromous brown trout (Salmo trutta L.), a highly migratory fish, depends on the impact of sea trout movement and their effective dispersal (i.e. movement followed by reproduction), that are difficult to quantify because natal origins of sea trout are unknown. We genotyped 11 microsatellite loci from 846 juveniles and 615 sea trout collected, respectively, by electrofishing across 78 tributaries and trapping across 7 fish traps, located in southwestern France. Juveniles were used as a reference for the background population genetic structure and enable us to quantify and dissociate movement of anadromous sea trout from effective dispersal. We found a strong hierarchical structure of juvenile population in accordance with sea trout movement and contemporary levels of gene flow. We found a high site fidelity movement of sea trout, and an asymmetric northerly Spanish sea trout movement. This movement does not necessarily result into effective dispersal. These findings have an important implications for regional management practice and broader understanding of brown trout population functioning