How many freshwater pearl mussels live in Estonia?

The one and only FPM population in Estonia is spread along ca 21 km long section of river Pudisoo, situated in Lahemaa National Park. Previous estimations of the population size vary from 10 thousand to 40 thousand individuals. It is clear, that the population is isolated, and the size is close to the critical level, but exact numbers have been missing.

In the LIFE Revives project funded by the EU LIFE programme, Estonian State Forest Management Centre, RMK, will carry out a thorough FPM inventory in the beginning and end (2027) of the project. The first inventory round took place in summer 2022.

RMK team, led by FPM specialist Aune Veersalu, counted a total of 25 000 specimens. Sadly, this finding did not eliminate concerns about the future of the species. It was revealed that the only Estonian population consists of mostly old individuals. The lack of sufficient number of younger mussels in the river means, that the population is at risk of decline due to natural aging and a lack of new generations.

However, there is also some good news. During the inventory, a total of 100 young individuals in different parts of the habitat were found. It is a promising sign, that there still are spots, where the juveniles can survive and thrive.

This all highlights the importance of careful inventory. Surviving young specimens give some hope that restoration efforts by RMK would benefit the survival of FPMs and other aquatic species in River Pudisoo.

In the following years, RMK is planning to restore several peatlands within the River Pudisoo catchment, build wooden structures to improve the condition of the riverbed and reintroduce more than 5,000 young FPM individuals into the river.

Text and photos: Katrin Kaldma, RMK freshwater pearl mussel specialist