MIGRATORY BEHAVIOR OF ADULT WILD AND ESCAPED FARMED ATLANTIC SALMON, SALMO-SALAR L., BEFORE, DURING AND AFTER SPAWNING IN A NORWEGIAN RIVER

The migratory behaviour of adult wild and escaped farmed Atlantic salm on, Salmo salmo L., before, during after spawning in the River Namsen, Norway, was analysed using radio telemetry. The fish were caught, rad io tagged and released into the fjord between 7 and 25 km from the riv er mouth. A significantly higher proportion of wild (74%) than farmed (43%) salmon was subsequently recorded in the river. Wild salmon (33%) were more frequently captured in the sea and in rivers than farmed sa lmon (14%). The migration speed from release to passing a data logger 11 km upstream from the river mouth was not significantly different be tween wild (20.6 km day(-1)) and farmed (19.8 km day(-1)) salmon. Wild salmon tagged when water now in the river was increasing had a signif icantly higher migration speed than wild salmon tagged when water now was decreasing. This was not true for farmed salmon. Farmed salmon wer e distributed significantly higher up the river than wild salmon durin g spawning, although both types of fish were found together in spawnin g areas. Thus, there was no geographical isolation to prevent spawning between wild and escaped farmed salmon. Farmed salmon had significant ly more and longer up- and downstream movements than wild salmon durin g the spawning period. Unlike farmed salmon, the number of riverine mo vements by wild salmon increased significantly when variation in water now increased. A smaller proportion of wild (9%) than farmed (77%) sa lmon survived through the winter after spawning.