Endangered relict salmon - about human impact
The Namsblanken is a relict salmon that only lives in the upper reaches of the river Namsen in Trøndelag. There are now few Namsblanken left. In this assignment, using a text, a pair of scissors and two A4 sheets, you will understand why.
Competency goals for grade 7, Science
- reflect on how technology can solve challenges, create opportunities and lead to new dilemmas.
- explain the importance of biodiversity and implement measures to preserve biodiversity in the local environment.
- explore and describe different food webs and use this to discuss interactions in nature.
With every cut we make in the sheet, the habitat of the Namsblank becomes smaller.
Here's what you need to know first
The Namsblanken is a relict salmon. Relict salmon is extremely rare. The word relict means "something that has been left behind".
The Namsblanken can only be found in the upper reaches of the river Namsen in Trøndelag. Here it lives its entire life. Unlike other salmon, it never travels to the sea. The Namsblanken thrives best in fast-flowing water.
The Namsblanken has lived isolated in Namsen for around 9500 years. It was land uplift after the last ice age that isolated the Namsblanken. This created some large waterfalls. The salmon that lived above the waterfalls continued to live there and became the Namsblanken. The salmon below the waterfalls continued their lives there, migrating to the sea. The Namsblanken originates from Atlantic salmon.
Until just 60 years ago, there was a lot of Namsblank. Now there's little left, and it could disappear before our eyes. Here's what happened.
Task
Find a pair of scissors and an A4 sheet of paper. Read the text below and cut away.
The sheet is the Namsblanken's habitat as it was before we humans began to change it. For 9500 years, the namsblanken had the entire sheet as its habitat.
We go back 70 years and look at what has happened up to the present day.
We needed electricity. Much of the water in the upper reaches of the river was diverted elsewhere, and through several hydropower plants. In the areas where the power plants took water from the river, the river became narrower. This meant that the habitat of the Namsblanken became smaller. At the same time, the speed of the water became slower. Cut away two strips (1 cm) on each long side of the sheet.
People thought it was a shame that the river was so narrow and wanted it to be as wide as before. To achieve this, they built four thresholds in the river. The thresholds slowed down the water and the river became wider (see picture below). The result was that the speed of the water became even slower. Cut out four equilateral triangles (the sides should be about 3 cm) from the sheet.
We needed more electricity and found that there was more energy to be extracted from the river. So four new power stations were built. On the upper side of these power stations, the water became almost like calm lakes. Cut out four smaller squares (the sides should be about 2 cm) from the sheet.
Some people thought it would be nice to help the sea-migrating salmon up the large waterfalls. Fish ladders were therefore built. The Namsblanken and the sea-run salmon are the same species and can have children together. There was competition for both hiding places and food. Cut away a triangle (the sides should be 2 cm).
Some fishing tourists were on a fishing trip far up the river. Although it is forbidden, they were fishing with live bait. The bait they used was earwigs. This is an alien species of fish in the river, and it can carry diseases. The oyster escaped or was released, and it quickly spread down the river. It competed with the Namsblanken for both hiding places and food. Cut away a corner of the sheet.
Now you can study the sheet. This is what's left of the Namsblanken's habitat after everything we've done to the watercourse over the past 70 years. The bits that have been cut away are habitats that have now become unusable for the Namsblanken.
What do you think we should do next?
Is it possible to repair some areas by gluing some pieces back on?
Hydroelectric power plants
In a hydropower plant, the energy in flowing water is converted into electricity. The flowing water accelerates a water wheel called a turbine. The conversion takes place in a machine called a generator, which is connected to the turbine.
Threshold
A sill is a low dam that dams up a section of the river. Above the threshold, the river widens, but the speed of the water slows down.
Fish ladder
A fish ladder is an artificial access route for fish. Each step in the staircase is filled with water. This enables fish to get past a barrier in the river, such as a high waterfall.
For the teacher
This assignment is a concrete example of how human activity can lead to reduced habitats for many animals. The assignment also touches on topics such as power generation and land uplift.
First, set aside time to review the text and editing. Each student can do this on their own, but it also works well to do this together. Pass the sheet and scissors around so that several people can cut.
Once the sheet is cut, you can reflect and discuss in class:
What do you think should happen next?
- Is it possible to repair anything (can we glue some pieces back on)?
- Can we continue "cutting" (for example by building more power plants)?
To test your reading comprehension, you can use these questions:
- Why were there fewer Namsblanks when the river became narrower? The living areas became poorer. There weren't enough hiding places and food for as many.
- Why can we say that the habitat of the Namsblanken became smaller when the thresholds were built and the river became wider? The Namsblanken likes fast-flowing water.
- Why can we say that the habitat of the Namsblanken became smaller when the sea-migrating salmon came to where the Namsblanken was? There was competition for food and space.
- Why is it harmful to introduce a new species into a natural environment? Diseases, competition for food and space.
Student booklet
The Nasjonalt villakssenter works for a stronger wild salmon and wants to promote the stream as an educational resource. Bring experiences from the classroom and put them in context with experiences outside. Many schools in Norway have a local stream. Even in our largest cities, there are streams that can be visited. Contact us for assistance, tips and professional support.
The student booklet "Who lives in your river?" can help with both preparation and follow-up work.