Marine life of the sea trout

An understanding of when and where sea trout Salmo trutta L. are located at sea is essential to the effective management of local populations and in evaluating their vulnerability to salmon lice and other anthropogenic threats. Here we review the available literature on sea trout life-history strategies, behaviour and habitat use in the marine environment, including feeding, growth, survival and homing. There is considerable variation in life-history strategies among individuals and populations and in the timing and duration of marine migration(s). Females tend to adopt the anadromous strategy more than do males. Smolts typically leave rivers in spring (March-June in European rivers), but also at other times of the year. Postsmolts may remain at sea during the summer and return to freshwater to over-winter; adults thereafter spend summers at sea and winters in freshwater, or they can remain at sea until they later return to freshwater for spawning. Sea trout frequently are recorded at sea during winter and can tolerate full-salinity sea water at water temperatures as low as 1-2 degrees C. Sea trout often remain within 80 km of their river of origin, but also may undertake longer-distance marine migrations (> 500 km). The duration and timing of marine migration both are likely governed by trade-offs between mortality risk and growth potential in different habitats, and the most beneficial strategy may vary among individuals and populations. Reduced marine growth and increased marine mortality will reduce the benefit of marine migrations and may result in selection against anadromy.