River mussels and pearls - a math problem
The river mussel used to have a different name. It was called the river pearl mussel. Find out why it had to be renamed in this literacy and numeracy task.
Competency goals for grade 7, Science
- distinguish between observations and inferences, organize data, use cause-and-effect arguments, draw conclusions, assess sources of error and present findings.
- explain the importance of biodiversity and implement measures to preserve biodiversity in the local environment.
River mussels. Photo: Bjørn Medjell Larsen, NINA
How many river mussels had to die?
The river mussel is now protected. In the past, people used to catch river mussels to see if there were pearls inside. The hunt for pearls has wiped out the river mussel in many rivers. In the 18th century, the Queen of Copenhagen had exclusive rights to all pearls found in Norway.
It is very rare to find pearls in river mussels. We have to kill at least a thousand mussels to find one pearl, and out of a thousand pearls, only one is fine enough to be used for jewelry.
Norway's heir apparent crown
This crown was made in 1846 and features 32 river mussel pearls.
After a drawing by Johannes Flinto
Tasks
How many river mussels had to die to make Norway's heirloom crown?
Why do you think the name was changed from river pearl mussel to river mussel?
Protected species
The river mussel is protected. This means that you are not allowed to catch them.
If you see river mussels in the river or stream, leave them alone. If you try to open a mussel to see what's inside, it will die.
In Norway, all wild animals are protected. Some are protected all the time. Then we say that they are totally protected. Other species are only allowed to be hunted, fished or caught at certain times.
The river mussel is protected all year round (totally protected), while the moose can be hunted in the fall.
Think about these questions and discuss them in class:
Do you know of any other species in Norway that are totally protected?
Why is it important that some species are totally protected?
Do you think the total eradication of species is a good way to preserve biodiversity?
What can you do to help preserve biodiversity?
"The one who wears pearls"
The Latin species name is Margaritifera margaritifera. It means "the one who wears pearls".
For the teacher
This is a calculation with really big numbers. On average, one in a thousand river mussels has pearls. One in a thousand pearls is fine. In other words, to find one fine pearl, you need to pick 1 million mussels. To get enough pearls for the heirloom crown, at least 32 million river mussels had to die.
The start of a pearl is a grain of sand that irritates the mussel. The mussel encapsulates the grain of sand with mother-of-pearl from its shell.
If you want to set aside some extra time for the river mussel, we recommend taking a look at Perler for svin, which can be downloaded from Ut i naturen (2009 season) on NRK. The program lasts for 24 minutes.
On pages 28-31 of the student booklet Who lives in your river? you will find more text and exercises about the river mussel.
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.