Relation of grilse to salmon ratio to environmental changes in several wild stocks of Atlantic salmon (Salmo salar) in Iceland

The grilse to salmon ratio of each smolt class of Atlantic salmon (Salmo salar) during the last three decades were examined using data from catch records and from direct counter data in several rivers in western and northern Iceland. The counter data show that the catch data in Icelandic rivers reflects the number of spawners entering the rivers. Both long- and short-term changes in the grilse to salmon ratio were seen. Climatic changes can be responsible for long term changes in sea age composition of Icelandic salmon stocks. Short-term changes in the ratio can be explained by changes in marine conditions that influence the survival of salmon during their second year at sea.