Return migration of Atlantic salmon in the River Tana: phases of migratorybehaviour

From a total of 174 multi-sea-winter Atlantic salmon radio tagged in the Ta nafjord (northern Norway, 70 degrees N) during 1992 and 1993, 48 Atlantic s almon were followed from entering the River Tana until spawning. Three phas es were identified: (1) migratory, direct or stepwise migration to, or clos e to the position held at spawning; (2) search, movements both up and down river at or close to the position held at spawning; (3) holding, a period w ithout movements prior to spawning. During the migratory phase, Atlantic sa lmon migrated directly to near the spawning area, or stopped between one an d nine shorter periods during the upstream migration. Number of stops incre ased with increasing migratory distance in 1993, but no such correlation wa s found in 1992. The highest migratory speeds were recorded in the lower pa rts of the river. A distinct change in migratory pattern was found in 67% o f the Atlantic salmon near or at the area held at spawning. Most common was a search phase of erratic movements with more than one down river movement . After the movement terminated, 96% of the Atlantic salmon had a period wh en no or little movement was recorded until spawning (on average 55 days in 1992 and 51 days in 1993). There was no preference for staying at, up or d own river from the spawning area during this holding period. Early ascendin g Atlantic salmon migrated to spawning areas further from the mouth than th e later arriving Atlantic salmon in 1993, but not in 1992. The proportion o r time spent on the migratory phase increased, while the proportion of time spent on the holding phase decreased with increasing distance to the spawn ing area. (C) 2001 The Fisheries Society of the British Isles.