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Summary of fjordic migratory routes of wild- and hatchery-reared Atlantic salmon smolts

To improve our knowledge on the mortality in the first marine stage of Atlantic salmon post-smolts, we developed and used telemetry techniques to monitor the fish movements in the marine environment with different salmon lice pressure. Wild Atlantic salmon post-smolts were, similar to hatchery-reared post-smolts, not passively drifting with the current, but actively swimming and the fish moved in random directions in relation to the water current.

Atlantic salmon post-smolts stayed for a longer time in the inner part than in the outer parts of the fjord system, but in contrast to sea trout, migrated through the whole fjord system into the ocean. Neither salmon lice infection nor pharmaceutical prophylaxis had any effects on survival and rate of progression of migrating Atlantic salmon post-smolts.

The proportions and swimming speed of fish recorded did not differ between wild and hatchery-reared post-smolts and indicate that the behaviour of hatchery-reared Atlantic salmon post-smolts may be representative for wild salmon. This information will be used to develop a model for simulating the risk of salmon lice infestation in different areas used by Atlantic salmon post-smolts. By using this model we may better evaluate where and when the observed infestation is acceptable or not.

Reported by

Norwegian Institute for Nature Research
Tungasletta 2
N-7485 Trondheim
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