  Data from seven data storage tags recovered from Atlantic salmon marked as
smolts were analyzed for depth movements and patterns of deep diving during the
marine migration. The salmon mostly stayed at the surface and showed diurnal
activity especially from autumn until spring. During the first months at sea
the salmon stayed at shallower depths (< 100 m). The salmon took short deep
dives (> 100 m), that were rare or absent during the first summer at sea but
increased in frequency and duration especially in late winter. The maximum
depth of the dives varied from 419 to 1187 m. Most of dives were short, (< 5
hours) but could last up to 33 hours. The duration of dives increased in late
winter until spring and the overall depth and maximum depth per dive increased
exponentially over time. The initiation of the dives was more common in
evenings and at night, suggesting nocturnal diving. We hypothesized that deep
diving is related to feeding of salmon as mesopelagic fish can be important
food for salmon during winter.
