Atlantic Salmon Smolt Migration in the Rivière Saint-Jean, QC and the Gulf of Saint Lawrence: Effect of Environmental Variables and Identification of Migration Pathways

Limited work has been done on the ecology and ocean migration pathways of Atlantic salmon (Salmo salar) from rivers originating on the North shore of the Gulf of Saint Lawrence (Canada). It has been hypothesised that post-smolts from these rivers travel north-east following the coastline until they reach their feeding grounds in the Labrador Sea. In 2009 and 2010, we investigated the migration patterns of smolts from the Rivière Saint-Jean (50°17'0"N, 064°20'10"W). We surgically implanted uniquely coded acoustic transmitters in 44 and 49 smolts in 2009 and 2010 respectively, and placed hydro-acoustic receiver arrays at fixed locations in the river, in the Jacques Cartier Passage and in the two openings of the Gulf of St. Lawrence to the Atlantic Ocean (complete coverage across the Strait of Belle Isle and partial coverage across the Cabot Strait; > 600 km from the release site). The objectives of the research were to investigate the effects of environmental factors (water temperatures, diel and tide cycles) on the characteristics of seaward migration of smolts and to define emigration pathways of post-smolts. The onset of the smolt run started at river water temperatures of approximately 10°C. The majority of downstream movements of the acoustically tagged fish occurred at night or during twilight. Most tagged smolts entered the estuary at the onset of the ebbing tide. Post-smolts departing the estuary did not follow the coast line but instead moved rapidly south and south-west, almost perpendicular to the coast. Two post-smolts were detected 45 km south of the estuary, 4 to 5 km off the west point of Anticosti Island suggesting that they did not follow the shortest route to their feeding grounds in the Labrador Sea. Only one tagged fish was detected exiting the Gulf of St. Lawrence. This post-smolt crossed the Strait of Belle Isle line, between Newfoundland and Labrador, 44 days after leaving the river mouth for a minimum estimated travelling speed of 14.4 km/day.