Habitat use and dispersal of post-smolt sea trout Salmo trutta in a Scottish sea loch system.

Post-smolt anadromous brown trout Salmo trutta, sea trout, from two Scottish west coast rivers, the Balgy and Shieldaig, flowing into adjacent sea lochs were tracked simultaneously using arrays of moored acoustic receivers to determine dispersal patterns and loss rates. Fish tended to stay close to their natal rivers for the first 14 day after entering the sea, during which time about half the fish were lost to the study. Although initially the overall pattern of dispersal was similar for individual fish from both rivers, towards the end of the study the groups had converged into one of the loch basins. There were also pronounced individual differences in habitat use with all those fish detected for >42 days exhibiting different patterns of habitat use. Loss rates were similar between the two rivers despite differences in the range of air-breathing predators to which the fish were initially exposed. These findings suggest that any management of predators or other mortality agents should be targeted towards mouths of rivers during and immediately following smolt emigration.