Marine feeding areas and vertical movements of Atlantic salmon (Salmo salar) as inferred from recoveries of data storage tags

We released 598 Atlantic salmon (Salmo salar) hatchery smolts in a river in Iceland in 2005 and 2006 tagged with data storage tags recording temperature and (depth) continuously. Five salmon returned in 2006 and two in 2007, all spending 1 year at sea. The complete temperature and depth profiles of the whole ocean migration were measured. The salmon stayed close to the surface most of the time and showed diurnal behavior, staying at slightly deeper waters during day. The salmon were in temperatures from 6 to 15 degrees C, with warmer temperatures in the summer. We compared the fish-recorded temperature with sea surface temperature from an available National Oceanic and Atmospheric Administration database to locate the fish at different times. Utilizing the diurnal behavior of the salmon, we estimated solar noon each day during winter. Sea surface temperatures and diurnal activity were used to estimate daily locations using established Hidden Markov Model for fish geolocation. The salmon in the study stayed southwest of Iceland in the Irminger Sea during the first summer months, but in the fall they moved towards the Faroes Islands and then back to the Irminger Sea where they stayed, until returning to the river. The salmon also took shorter and deeper dives (>100 m) during the latter part of their ocean migration.