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Summary of fjordic migratory routes of wild- and hatchery-reared sea trout smolts

To improve our knowledge on the mortality in the first marine stage of sea trout post-smolts, we developed and used telemetry techniques to monitor the fish movements in the marine environment with different salmon lice pressure. Manual tracking of wild sea trout post-smolts showed that they were actively swimming in the fjord.

The actual movements of sea trout were in all compass directions, with no systematic patterns. By automatic tracking it was shown that the rate of progression of wild sea trout smolts was different during their outward migration from the outlet of the home river.

Both wild- and hatchery-reared sea trout post-smolts had a slower rate of progression between different receiver sites than wild- and hatchery-reared Atlantic salmon post-smolts and remained to a larger extent compared to Atlantic salmon post-smolts in the inner part of the fjord system. It was also shown that the wild sea trout post-smolts stayed rather closer to the shore than in the middle of the fjord.

This information will be used to develop a model for simulating the risk of salmon lice infestation in different areas used by sea trout 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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