Brown trout may live the entire life in freshwater (resident trout) or occasionally migrate to sea (sea trout). In theory, individuals should migrate to sea if such behavior increases reproductive success. It has been shown, that migratory differences not only rely to resident or migratory individuals. Within a seaward migrating group of trout, large differences in distance migrated away from the river can often be found. Some stay close, while other migrates far away. In this project, we will aim to map physiologically differences between juvenile trout that become residents or migrate to sea and between short and long distance migratory sea trout. Seaward migration is a behavior that can be expected when the gain for the individual fish is higher than the cost. Consequently, one can expect that this behavior will be changed or disappear if sea conditions are so negative for sea trout that it loses reproductive potential by migrating to sea.