Freshwater pearl mussels in danger of extinction to receive a rearing station 26.03

The freshwater pearl mussel is a long-lived invertebrate species whose ageing and quickly diminishing population can now only be found in the waters of just one Estonian river. Sadly, this population of freshwater pearl mussels is no longer viable, being composed fully of specimens that are 40 years old or older. No young mussels have been discovered in the past decade.

Despite the old mussels procreating, their young are not able to survive in the diminished environmental conditions of the river. Young mussels spend the first six years of their lives dug into the gravel at the bottom of the river. As the riverbed becomes muddier and the water quality drops, so do the chances of the mussels surviving. Efforts to clean the river of silt have begun with the goal of restoring the riverbed to a state that is habitable for the mussels. In order to keep the species alive while the river is being cleaned, the mussels must be raised in artificial conditions during the most critical stages of their life, after which the population will be returned to the river.

"In order to save the freshwater pearl mussel population, we must restore their river and its basin to their natural conditions. To achieve this, we must lessen the influx of silt into the river, close any ditches that connect to it and control the beaver population," said Head of RMK's Põlula Fish Rearing Centre Kunnar Klaas.

The strong presence of a brown trout population is also imperative for the reproduction of freshwater pearl mussels. Newly born mussels create a symbiotic relationship with the trout, without which they cannot survive.

"The freshwater pearl mussels' dependency on other species shows us the importance of securing the integrity of the entire ecosystem through nature conservation," said Minister of the Environment Tõnis Mölder. "Just as it is proof that a river's ecosystem is only as strong as its weakest member, building the rearing centre and cleaning the river will benefit all denizens of those waters."

The full restoration of the habitat will take years, and until this is accomplished, the species must be conserved by raising mussel offspring in an artificial environment during their critical development period. Once the mussels are able to live without artificial support, they will be returned to the river.

Last year, a number of experiments were conducted in Põlula where young mussels were grown using water from their native river. These showed positive results. "Mussels can be grown in a lab for about a year; however, rearing the mussels to a suitable age where they would be able to survive independently requires a growth environment by their home river. The rearing station for these mussels will thus be built near their river. We hope that we will be successful in saving this population of freshwater pearl mussels from extinction," said Kunnar Klaas hopefully.

The freshwater pearl mussel rearing centre will be built as a part of the European Union Cohesion Fund's measure "Preserving and restoring protected species and habitats" and its activity "Ex-situ species conservation investments". The fund will grant the project 182,000 euros in accordance with the decision made by the Ministry of the Environment. The project will be carried out in the period from 2021-2023 by RMK Põlula Fish Rearing Centre who will add an additional 32,000 euros to the project as self-financing.

The freshwater pearl mussel action plan can be found on the home page of the Environmental Board. Additional information on RMK Põlula Fish Rearing Centre can be found on their home page.

Further information:
Kunnar Klaas
Head of RMK Põlula Fish Rearing Department
kunnar.klaas@rmk.ee
+372 527 8245

Sille Ader
Head of RMK Communications Department
sille.ader@rmk.ee
+372 5666 5896

Marju Kaasik
Lead Specialist of the Public Relations Department of the Ministry of the Environment
marju.kaasik@envir.ee
+372 5133 165