The effects of surgically-implanted dummy radio transmitters on the behaviour of wild Atlantic salmon smolts

The social behaviour of Atlantic salmon smolts was evaluated during their migration period under controlled conditions in an experimental stream tank. Agonistic behaviour, dominance, distance to nearest neighbour, and distance from substrate were examined pre- and post-surgical implantation of dummy radio transmitters (2.4-4.3% body weight). Smolts were able to quickly equilibrate after transmitter insertion. Social ranking changed in nine of the eleven trials with four fish, and in only one of the five trials with pairs. No significant differences were found (p > 0.05) in any of the behavioural parameters measured. Overall, the only effect on smolts surgically implanted with radio transmitters was a large shift in dominance. The presence of an antenna also elicited aggressive attacks from other individuals.