Salmo trutta (sea run brown trout)
Sea trout or sewin are a migratory form of brown trout. Their adult lives are spent feeding in the sea. They return to Welsh rivers to breed each year – typically during the summer months.
Fresh run sewin are silver in colour, but eventually turn darker and begin to look more like brown trout in the autumn.
Sea trout can vary in size from 30cm schoolies all the way to 80cm plus monsters that can weigh 10kg. They are common in many rivers in Wales, particularly those with poor nutrients and good tributary spawning – good sea trout rivers generally tend to be poor brown trout rivers.
The best rivers are the Towy and tributaries, plus the Dovey and Teifi. There are many others with good runs, including the Ogmore, Rheidol, Glaslyn, Tawe, Mawddach and Conwy.
Sea trout are usually fished for at night in Wales, using fly fishing techniques.