Scottish Marine and Freshwater Science Vol 6 No 12

It is widely acknowledged that Atlantic salmon (Salmo salar) sub-stocks exist in Scottish rivers. These sub-stocks are associated with diverse life-histories, relating to different environments and pressures. However, there are significant challenges associated with the analysis of populations at the sub-river scale. This report investigates the potential for assessment of fish populations at a sub-river scale. A sophisticated mathematical model was used to separate salmon from a single river (North Esk, eastern Scotland) into three sub-stocks, based on the number of years the adults have spent at sea (their sea-age) and the month of the year in which the adults return to freshwater to breed (their run-timing).