Over-summering behaviour of Atlantic salmon Salmo salar returning to rivers in the Cromarty Firth, north–east Scotland

In 2005, a high percentage (50%) of Atlantic salmon Salmo salar fitted with acoustic transmitters, which entered rivers in the Cromarty Firth area of north–east Scotland dropped back to the estuary and ascended adjacent rivers after 33–80 days of freshwater residence. Fish residing in non-natal rivers generate mixed stock fisheries, and movements of fish between rivers could increase the risk of disease transmission between catchments.