Food restriction prior to release reduces precocious maturity and improves migration tendency of Atlantic salmon (Salmo salar) smolts

Since food availability is known to affect both the precocious maturation and start of feeding migration in wild juvenile salmonids, we examined if a reduction in otherwise plentiful feeding in hatcheries could improve migration tendency and the subsequent survival of released Atlantic salmon (Salmo salar) smolts. A reduction in diet lipid content and feed ration (FR) the previous spring and in FR in the winter prior to release proved efficient; spring-diet treatment halved the proportion of mature males in the autumn prior to release, and a reduction in FR in the winter prior to release decreased latency before leaving the stocking site. In addition, a reduction in FR in winter affected the onset of migration, improved migration speed, and defined the direction of migration downstream in controlled experiments. However, diet manipulations neither affected the swimming endurance nor improved the generally poor tag recapture rates. We conclude that reduced FR at specific times could be used to reduce both precocious male maturity and improve the migration tendency of released salmon.