What factors influence which young trout become smolts and migrate to sea?

The process is not yet fully understood. Although there is strong evidence from scientific studies indicating a genetic basis to the seagoing tendency, the rearing environment also has been shown to be important. For example, artificial rearing of sea trout progeny can increase the proportion that remains in fresh water.   Incubation of the eggs at water temperatures differing from natural cyclic levels and improved food availability for the fry and parr held in tanks, providing a ‘soft’ life-style  compared with life in the wild, can change normal seasonal patterns of growth and advance the onset of sexual maturity, favouring the adoption of resident over migratory behaviour.