New paper: can brown trout escape a hydropower tunnel?

Brown trout are key players in our freshwater and coastal ecosystems, moving between rivers and the sea to make the most of different habitats throughout their lives (also known as sea trout, searun trout, anadramous trout). One important stage is the blenkje (also called finnock): young trout that return to freshwater after their first summer at sea, but before they mature. Their survival in rivers is crucial—if they make it, they can head back to sea, grow, and eventually reproduce.

View of the lake Vassbygdivatnet

In the Aurland River system, a hydropower storage plant drain water from the lake between mid September to late April, which is then transported to the fjord. Trout can enter the tunnel leading to the storage plant, but a grid has been placed to prevent fish from passing the turbine. To understand the risk, we released fish into the tunnel both before and after the turbines started running.

What did we find?

• More fish escaped when the power station was inactive (86%) than when it was active (56%).

• They also left faster during inactive periods (about 29 days compared to 44 days).

• Two fish even survived being pulled through the turbine and continued downstream to the fjord.

• Data from accelerometer tags showed that swimming was more demanding when the tunnel was operating.

These results suggest that hydropower can make life harder for young trout, but some still manage to survive. Understanding these challenges is important for designing solutions that protect migratory fish while producing renewable energy.

Read the paper here: Blenkje paper!

Thanks to the Norwegian Research Council for funding the LaKES project (nr. 320726).