Royal Netherlands Institute for Sea Research

Sea Trout

The sea trout starts its life in fresh water and lives there for four to five years. Photo: P. Dunbar

Life history

The salmonids belong to a family that easily forms new species. The sea trout has more or less the same life history as the atlantic salmon, but also has two family members who prefer to stay in fresh water: the brook trout and the brown trout. The latter especially is very similar to the sea trout, except this species never leaves fresh water.  The sea trout starts its life in fresh water and lives there for four to five years until it is about 20 cm long. It eats mainly insects, benthic animals and small fish. Once it starts its life in the sea it eats mainly fish and quickly grows to about 1 metre over four years.

Migrating sea trout

It returns to the rivers in autumn when most of the older fish spawn; the smaller ones join the journey so that they know the way once they are adults. The most striking difference with salmon is the fact that the sea trout returns to sea after spawning. So in the Wadden Sea where we have our stake nets to monitor the fish abundance we only catch migrating sea trout on their way to open sea or to the rivers. On its way to the rivers the sea trout changes its outline like a salmon. The lower jaw of the male curves upwards and its scales become strong and covered in a slimy layer in order to adapt to the fresh water environment. The food also changes; small fishes, worms and insects (fly fishing!) are the main target. We see this spawner here mainly in September and the beginning of October.

Swim ways

In contrast with salmon we still have a good stock of sea trout in Holland and the forecast is good now that the swim ways from sea to fresh water are restored and their spawning grounds can be reached.