Migration and swimming depth of Atlantic salmon kelts Salmo salar in coastal zone and marine habitats

Factors influencing the migration and swimming depth of Atlantic salmon kelts Salmo salar L. within the York Estuary and Gaspé Bay (Québec, Canada), and in the Gulf of St. Lawrence between Gaspé Bay and the Strait of Belle Isle (Newfoundland, Canada) were studied using acoustic telemetry. In 2006 and 2007, a total of 49 kelts were tagged with acoustic transmitters equipped with depth sensors, released in the river delta leading into the estuary, and tracked using a fixed receiver array within the estuary and the bay. A large variation in migratory behavior existed, with some kelts making a direct, strongly oriented traverse across the estuary and bay, and others showing multiple changes in orientation. There was long-term residence (typically several weeks) in the river delta and rapid migration once kelts reached the estuary and bay resulting from seaward swimming, with a net seaward movement even on a flood tide. Diving was more frequent during daytime. It was hypothesized that diving may have been related to feeding and/or the identification of more temporally consistent sub-surface salinity gradients or current flow directions. The patterns of migration within the coastal zone were similar to those identified for smolts, implying a universal pattern of coastal zone migratory behavior in both smolts and kelts. Migration speed within the marine habitat was dependent on date of departure from Gaspé Bay, which in turn was dependent on the length of time kelts had remained in the delta. It was hypothesized that extended feeding within the delta allowed kelts to improve their physical condition, enabling them to migrate more rapidly in the marine habitat.