Effects of tagging on migration behavior, survival and growth of hatchery-reared Atlantic salmon smolts – an experimental study (#109)
Securing the survival of downstream migrating smolts is one of the key factors for re-establishment of salmon populations in regulated rivers. Information on smolt behavior and survival are used for planning mitigation measures, such as downstream migration routes passing weirs and powerhouses. Such information is usually based on tagged fish. However, tagging can have variable negative effects on behavior, survival and growth of fish, and considerable tag loss may also occur. Therefore, understanding tagging effects on smolts is important for making relevant conclusions and recommendations for mitigation measures. We examined the effects of four different tagging methods (PIT tag, T-anchor tag, Carlin tag and dummy radio transmitter) on the survival, behavior and growth of salmon smolts during their downstream migration in semi-natural circular channels during a natural migration period in spring. In addition, possible differences in tag loss rates between tag types were examined. Survival of smolts was high (range 99.4–100%) and tagging wounds healed well in all tagging groups. Tag loss rates were low (range 0–2.5%) in all tagging groups, being highest in the dummy transmitter group. Only smolts tagged with dummy transmitters showed slower growth than untagged control fish. In addition, smolts tagged with a dummy radio-transmitter or a Carlin tag started their migration slightly later and showed less migration activity than fish with PIT tags.