Study of Atlantic salmon post-smolt movement in the Gulf of St. Lawrence using an individual-based model

This study examines the effect of environmental conditions and swimming behaviors on the movement of Atlantic salmon (Salmo salar) post-smolts (juveniles) in the Gulf of St. Lawrence (GSL) using an individual-based model (IBM). The IBM uses time-varying and three-dimensional currents and hydrography produced by an ocean circulation model combined with a numerical particle-tracking scheme where swimming behaviors can be specified. Various experiments are run using this IBM with the aim of gaining insight into the observed movements of post-smolts documented in a past field study. In that study, a post-smolt released from the Saint-Jean River on the north shore of the GSL in June 2010 was found to exit the GSL through the Strait of Belle Isle (SBI) to the northeast of the release area. Two other post-smolts, released later in June 2010, were detected near Anticosti Island (AI) to the southwest of the release area. The numerical results suggest that, for both the post-smolt(s) that moved to the SBI and towards AI, the ambient near-surface circulation patterns favored their movements. In the case of movement towards AI, the travel times simulated using the simulated circulation pattern and a variety of swimming behaviors agree well with observations. For movement towards the SBI, an efficient swimming strategy is necessary in addition to a favorable circulation pattern in order for simulated travel times to be similar to observations. This study suggests two successful strategies for movement towards the SBI: (a) swimming with currents in favorable directions and against currents in unfavorable directions, and (b) swimming towards a series of target locations that define a migration route. The possibility that Atlantic salmon post-smolts originating from rivers on the north shore of the GSL may sometimes be confined to the GSL instead of migrating to the open ocean is consistent with past observational studies.