Programmed acoustic tags reveal novel information on late-phase marine life in Atlantic salmon, Salmo salar

This pilot study used programmed acoustic tags implanted into Salmo salar smolts, in conjunction with an extensive offshore marine receiver array, to investigate late-stage migratory behaviour and survival of returning adult salmon. A total of 100 smolts were tagged in 2020, and a number of individuals were successfully detected as returning adults in 2021. After detection efficiency was accounted for, 5-9 adults were estimated to have returned to the offshore array c. 45 km from the river mouth. A total of three fish were subsequently detected in the river. Losses of between 40% and 66% were evident during the final stages of ocean migration, and one tagged fish provided direct evidence of a predation event.

Automated summary

This pilot study used acoustic tags implanted in Atlantic salmon smolts and a marine receiver array to examine late-stage migration and survival of returning adult salmon. Out of 100 tagged smolts in 2020, some individuals were detected as returning adults in 2021. Considering detection efficiency, it was estimated that 5-9 adults returned to the offshore array about 45 km from the river mouth. Three fish were subsequently detected in the river. Losses of 40% to 66% were observed during the final stages of ocean migration, with one tagged fish providing evidence of predation.