This is one of Norway's rarest animals

The Namsblanken - one of Norway's rarest animals. Photo: Per Harald Olsen, NTNU

In the largest river in Trøndelag, there is an isolated population of small Atlantic salmon that never goes to sea.

Atlantic salmon are born in a river. There it lives for a few years as a small fish. Then it travels far out to sea to eat and grow. When it becomes large and sexually mature, it returns to its river to spawn. This is how salmon live in almost all the 1,500 salmon rivers in Europe. But not in the Namsen, the largest river in Trøndelag. Here there is an isolated population of small Atlantic salmon that never goes to sea. It's called the Namsblank and lives its entire life in running water. Why is this the case?

Land uplift after the ice age

During the last ice age, Norway was covered by a layer of ice almost three kilometers thick. This heavy ice pushed the land down more than 200 meters. Towards the end of the ice age, more than 10,000 years ago, Atlantic salmon swam in from the sea and up the river. Since the land was then pushed down, the Namsenfjord extended at least 100 kilometers further into the valley than it does today. Spawning salmon swam all the way up here to spawn.

Over the next few thousand years, the land rose considerably. The river became longer and the fjord shorter. More waterfalls were formed, and some became so high that the salmon were unable to jump over them. This meant that the salmon above the waterfall were isolated.

The Namsblanken is a mystery

The mystery is that Atlantic salmon still live above the waterfalls. All other similar stretches of river in Europe were emptied of salmon when the waterfalls became too high. The salmon migrated to the sea to grow large. No-one knows for sure why the salmon in the upper reaches of the Namsen did not do so. But scientists believe that water temperatures in Namsen were particularly low just after the Ice Age. As a result, the young salmon grew little and were not big enough to migrate out to sea. Perhaps that could be the explanation?

Are we eradicating the name tag?

For 9500 years, the Namsblanken lived undisturbed in the upper parts of Namsen. A lot has changed in the last 60 years. First, we used much of the water in the upper Namsen for power generation. This made the habitats much smaller. Since then, we have discharged toxic mining water and introduced the alien and harmful fish species, the oyster. We have built fish ladders for the large sea-migrating salmon, and this has wiped out the Namsblanken in some important habitats. Now there are plans to build yet another power plant that will harm the Namsblanken.

Scientists believe the Namsblanken may disappear from the upper parts of Namsen. Then it will be lost forever, because this is the only place it lives. What do you think we can do to help the Namsblanken?