Lene Klubben Sortland

1 Introduction Atlantic salmon (Salmo salar) are iconic for their homing capacity. As described extensively in literature, most Atlantic salmon are born in freshwater, migrate into the Atlantic ocean, and eventually return to their natal river (Foster and Schom 1989; Jonsson and Jonsson 2011; Klemetsen et al. 2003; McCormick et al. 1998; Potter and Russell 1994).

1 INTRODUCTION Migration between distinct environments has evolved for organisms to maximize their lifetime fitness, but it can sometimes be associated with great risks. The freshwater-marine transition of smolts is a critical phase of the lifecycle of anadromous salmonids.