NIVA Denmark has carried out a study in which eDNA from the rare river pearl mussel has been found in two tributaries to Varde Å – namely in the outlet from Ansager Å and at four locations in Holme Å. The study has been financed by the Aage V. Jensen Foundation, Varde municipality and the Danish Environmental Protection Agency.

We collected water samples in Varde Å, Linding Å, Ansager Å, Grindsted Å and Holme Å to map river pearl mussel occurrences using eDNA. The analyzes were performed on a digital droplet PCR platform that performs better than qPCR for small populations of rare species. eDNA was found from river pearl mussel in Varde Å near Varde Sommerland and upstream Vagtborg. In addition, eDNA was found from river pearl mussel in the mouth of Ansager Å and at four locations in Holme Å. For Ansager Å and Holme Å, these are new finds, where the river pearl mussel was thought to have disappeared. There is thus the possibility that there are source populations in Holme Å that can potentially form a recruitment basis for the recently restored section from Nordenskov to Varde å.

The full report in Danish can be read here.

Pictures taken during field word.