The diet of red-breasted mergansers (Mergus serrator) during the smolt run in N.E. Scotland: the importance of salmon (Salmo salar) smolts and parr

Salmon ( Salmo salar ) formed the largest proportion by mass offish found in the stomachs of red-breasted mergansers ( Mergus serrator ) shot during the smolt run in north-east Scotland. Salmon parr represented approximately two-thirds by mass of juvenile salmon eaten, whilst smolts were present in a smaller proportion than previously predicted. The median lengths of parr and smolts eaten were 70 and 115 mm, respectively; the latter being significantly smaller than the smolt population sampled during annual production estimates on the river.