Hard times for sea trout in the Gaula watercourse

Healthy streams, with no man-made barriers that hinder migration and spawning, should have a thriving population of sea trout fry and juveniles. The sea trout above have hatched and matured in four consecutive years. (Photo: Morten Bergan/NIVA)

Healthy streams, with no man-made barriers that hinder migration and spawning, should have a thriving population of sea trout fry and juveniles. The sea trout above have hatched and matured in four consecutive years. (Photo: Morten Bergan/NIVA)

“The sea trout stock in the Gaula watercourse is at its historic minimum. We have to monitor them and take urgent action, particularly in connection with the Water Framework Directive and the obligations it involves,” says Morten Andre Bergan at NIVA Midt-Norge.

Overshadowed by Atlantic salmon

The Gaula is renowned as Europe’s prime water system for Atlantic salmon. The sea trout [also known as salmon trout in the UK] in the Gaula, which generally rely on the same streams feeding into the river, have always been overshadowed by their more important ‘big brother’,” says Bergan.

The depletion of the sea trout stock in watercourses leading into the Trondheim Fjord triggered a ban on catches of the fish in several of the major rivers in Sør-Trøndelag County in 2009. All bycatches of sea trout by salmon fishers must be thrown back into the river.

Bergan recently lectured on the situation to a gathering including politicians and public servants in Melhus Municipality, the professional advisory council for the Gaula River watercourse and the chief manager of fisheries in Sør-Trøndelag County.

Morten Bergan returning a 5-kg sea trout to the river.(Photo: Morten Bergan/NIVA)

Morten Bergan returning a 5-kg sea trout to the river.(Photo: Morten Bergan/NIVA)

Bergan has been working with the Water Framework Directive and conducting monitoring studies in the region for the past four years. His evaluation of the ecological state of 35 important tributaries of the Gaula watercourse was based on these efforts.

A struggle for sea trout

“Water quality is deficient and living conditions for fish and bottom animals in many of the tributary streams of Gaula are very poor. This means there’s an urgent need for biological monitoring of the fish and we should implement comprehensive protective measures to revive stocks in several of the streams,” concludes Bergan.

About half the 35 streams investigated have been found unsatisfactory for propagating sea trout.

Moreover, the longest streams, which are potentially best suited for their replenishment, are the ones that are worst off.

Many of the streams have obstructions that keep the fish out or are seriously damaged compared to their natural state.

Human causes

“The areas that produce sea trout have diminished significantly. The main problem is man-made obstructions that hinder migration, chiefly from roads, railroads, covering up of streams, runoffs from agriculture and raw sewage from building developments,” says Bergan.

Source: www.niva.no

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