Migration of wild and reared Atlantic salmon (Salmo salar L.) in the river Simojoki, northern Finland

The patterns of upstream migration of wild and reared Atlantic salmon (Salmo salar L.) were studied in the river Simojoki in northern Finland using a trap net and radiotelemetry. In 1996, 16 wild and 22 reared salmon were tagged at a trap net placed in the river 4 km from the sea. The migration of wild and reared salmon was slightly different. The mean distance between the trap net and the furthest upstream observed point of reared multi-sea-winter salmon was 26.5 km compared to 16.3 km for wild salmon. The mean distance to the spawning place was 13.2 km for reared and 15.7 km for wild salmon. The reared salmon spent 43 days on an average before they settled down on their spawning areas compared to 31 days for wild salmon. There was a negative correlation between the migration distances and the length of the reared but not wild fish. Four fish descended below the trap but migrated later above it. In 1998, 13 salmon were tagged in the sea near the river mouth and nine of them ascended the river. Most of the salmon stayed below the study trap, which was set in the river 8 km from the sea, from I to 8 days (mean 3.5 days) before they continued their migration upstream. None of them entered the bag, but instead passed it revealing the unsuitability of trap net for salmon count. (C) 2002 Elsevier Science B.V. All rights reserved.