Atlantic salmon of wild and hatchery origin have different migration patterns

Hatcheries are frequently used to support or restore threatened Atlantic salmon populations. However, little is known about how rearing affects behaviour and fitness of hatchery adults that return to the river to spawn. We used acoustic telemetry to compare migration patterns exhibited by hatchery (N = 16) and wild (N = 12) Atlantic salmon spawners within a river system in Norway. Hatchery Atlantic salmon in this study were released as smolts and were identified by their missing adipose fin upon return to rivers after 1+ winters spent at sea. Hatchery-origin Atlantic salmon displayed aberrant reverse movement behaviour, by moving with frequent reversals between the river and the fjord, a behaviour that was not observed in any wild Atlantic salmon. No difference in survival and outmigration timing after spawning was found for the two groups. The observed effect of hatchery origin on behavior may have implications for stock assessments made to assess the progress of restoration in the river, particularly if behavioural differences impact catchability or detections of returning adult salmon. The consequences of different movement patterns are uncertain; however, movements are energetically costly and may ultimately impact the fitness of hatchery Atlantic salmon.

Automated summary

Hatcheries are commonly used for Atlantic salmon population support or restoration, but little is known about the impact of rearing on the behavior and fitness of hatchery adults that return to spawn. A study conducted in Norway compared the migration patterns of hatchery (N=16) and wild (N=12) Atlantic salmon using acoustic telemetry. The study found that hatchery-origin salmon exhibited abnormal reverse movement behavior, moving frequently between the river and fjord, which was not observed in wild salmon. Survival and outmigration timing after spawning did not differ between the two groups. The behavioral differences observed in hatchery-origin salmon may have implications for stock assessments used to evaluate restoration progress, particularly if they affect catchability or detections of returning adults.