Fishes in the Pasvik river – a life between power stations
One project at the station is about fish monitoring in the Pasvik river. The Pasvik river is the border to Russia and has a comparatively high biodiversity and contains 15 different species of fish; many bird species are living in the wet areas and it’s also used by many migrating birds.
To get an idea of the project, let’s have a look at the setting and the history of the river: In the Pasvik river, seven hydro-electric power stations are located, owned by Finnish, Russian and Norwegian energy producers. These power plants were built from 1951 until 1978 at places where waterfalls had been and changed the river system of the Pasvik river into a lake-like system where the different river parts are separated from one another. This change of the character also transformed the composition of fish species from fishes that live in fast-flowing rivers to lake-dwellers. The power stations dams cannot be passed by fishes, so each lake has its own species composition.
I had the possibility to visit the Skogfoss barrage, one of the power stations that are operated by a Norwegian company. For several decades, it has been equipped with a breeding facility to preserve the presence of the brown trout (Salmo trutta) in the Pasvik river, a species that has regional socio-economic importance because sport fishers from all over Europe as well as local recreational anglers come to try their luck and catch a big trout. The eggs are gained from trout that live further downstream. The hatchlings are raised over four years and each year about 5,000 brown trout individuals are being released in the Pasvik river.
Twice a week, researchers put fishing nets in the river overnight and the next morning, the big fish harvest was happening: all the perches (Perca fluviatilis), “sik” (Coregonus lavaretus), pikes (Esox lucius), vendances (Coregonus albula) and brown trouts (Salmo trutta) needed to be collected out of the nets, before the processing in the lab begun.
In the lab, the fishes were weighted, measured, and then further processed by having a look on the inside. Some of the fish had very interesting parasites on their gills, mouth, intestines, flesh or even liver. We took samples of those but first and foremost of the intestines (to have a look at the diet) and the flesh to examine the range of species, their age, if there is a pollution from heavy metals, and their genetics. Because there is no genetic exchange between the artificial lakes, the goal is to also detect if there is an effect of genetic bottlenecks detectable in the different fish species.