OCEANIC MIGRATION IN HOMING ATLANTIC SALMON

There appear to be two phases to the homing migration of maturing Atlantic salmon, Salmo salar, from feeding areas in the north Norwegian Sea to the home rivers in Norway: A first phase with crude navigation from the feeding areas towards the Norwegian coast and a second phase with more precise navigation in coastal and estuarine waters towards the home river. This was indicated by recaptures of Atlantic salmon individually tagged as: (1) smolts released in four Norwegian rivers; (2) smolts released on the Norwegian coast; (3) post-smolts transported from Norway and released in the feeding area north of the Faroe Islands during winter; (4) adults captured, tagged and released in the feeding areas in the Norwegian Sea outside northern Norway; and (5) maturing adults captured, tagged and released on the Norwegian coast and at the mouth of fjords. Experience gained as outward migrating smolts was required for salmon to navigate precisely along the coast, into the fjords and towards the home river, but not for the crude, eastward navigation from the feeding grounds towards Norway. Ocean currents appeared insignificant for the precise homing in coastal waters. Migration speed in the ocean increased with time during spring. Fish moving in the coastal current swam faster than those approaching the home stream in fjords. The return migration of Atlantic salmon is an active process where more than one set of navigational cues are needed. © 1993 The Association for the Study of Animal Behaviour. All rights reserved.