Modelling the migration of post-smolt Atlantic salmon (Salmo salar) in the Northeast Atlantic

The migration of post-smolt Atlantic salmon (Salmo salar) during their first 4 months at sea in the Northeast Atlantic was simulated using an individual-based model that combined a particle-tracking scheme with growth and behaviour routines. The migration was decomposed into both passive pelagic drift with the surface currents, provided by an ocean model, and active horizontal swimming behaviour. The active swimming direction was aligned with the surface current. Swimming speed was a function of body length and calculated from recaptured tagged salmon. Releases of particles in the model were made to the west of Ireland and to the southwest of Norway. The modelled post-smolt distributions were compared with the observed distributions, and a sensitivity analysis using different swimming speeds was performed. The strength and direction of the flow can transport the post-smolts towards areas with favourable feeding conditions. However, in some areas, the direction of migration was sensitive to interannual changes in the windforcing, leading the post-smolts to areas with a different environment and prey. Inclusion in the swimming behaviour of a preference for water with higher temperature and salinity displaced the northward migration more offshore, away from coastal areas.