Marine migration and habitat use of anadromous brown trout Salmo trutta

Abstract

The biology and ecology of anadromous brown trout Salmo trutta at sea is poorly understood. This study provided information on spatial and temporal distribution of sea trout in the ocean. The behaviour of 115 individuals (veteran migrants, 270-700 mm) was tracked by using acoustic telemetry in a fjord system during April-September in 2012-2013. Overall, fish spent 68% of their marine residence time close to river mouths (< 4 km). Most fish registrations (75%) were in near shore habitats, but pelagic areas were also used. The maximum migration distance of tagged fish was categorized as short (< 4 km from river mouth, 40% of fish), medium (4-~13 km, 18% of fish) or long (> ~13 km, 42% of fish). Long distance migrants had poorer body condition in spring prior to migration, used pelagic areas more often and returned earlier to freshwater than short and medium distance migrants. Marine residence time was 7-183 days, and was positively correlated to body length and smolt age, but negatively correlated to the date of sea entry.