The freshwater pearl mussel population in the Simojoki River can be saved with effective measures
Over 4,000 freshwater pearl mussels are living in the Simojoki River
In LIFE Revives, the population status of the freshwater pearl mussel in the Simojoki River was studied by the University of Jyväskylä and Alleco. Based on diving research done during 2022 and 2023, the estimated population size is around 4,600 individuals (Figure 1).
A precise, transect-based diving inventory was carried out in a known mussel area between Lake Toljanjärvi and the Kutusuo mire. In addition to this 11-km section, potential river stretches upstream up to Lake Simojärvi were also studied, but only a few individuals were found along this 18-km section. River stretches downstream from Lake Toljanjärvi were not included in this study, since no freshwater pearl mussel were observed there in previous inventories.
“At least the freshwater pearl mussel population of the Simojoki River has not declined,” says Juha Syväranta of Alleco, the leader of the diving research.
Syväranta reports that the population size even seems to have increased compared to the previous studies in 2002 and 2013 when the estimate was a bit over 3,000 individuals. This difference, however, is mainly due to the more accurate inventory method used in the recent study. Young individuals were not found, and the number of mussels had decreased in a stretch of the river that passes a peat production area.
“Without any further measures,” Syväranta says, “the freshwater pearl mussel population of the Simojoki River is going to die off, but there’s still hope.”
New freshwater pearl mussel generations have long failed to appear in the Simojoki River (Figure 2). The individuals found in the inventory study were all old and this is why the future of the Simojoki River freshwater pearl mussel does not look bright; no natural recruitment of new individuals is currently taking place. This may be a consequence of siltation of the riverbed, which is harmful for juvenile mussels. Another possible reason is the lack of Atlantic salmon, the required fish host for larvae of Simojoki River pearl mussels.
“For the Simojoki River freshwater pearl mussel, it would be necessary for salmon to ascend to mussel areas, or that the young salmon would be stocked in those areas,” says Professor Jouni Taskinen, the leader of LIFE Revives.
New juveniles expected
First aid is being provided to the Simojoki River pearl mussel population via the reintroduction of juveniles bred in captivity. These juveniles are produced and maintained at the Konnevesi Research Station of the University of Jyväskylä.
“Last summer, a few thousand small mussels were placed in gravel boxes in their home river,” says Heidi Kunttu, project manager of LIFE Revives. “If everything goes well, more mussels will be reintroduced next summer and released to the riverbed after couple of years.”
Further information:
- University of Jyväskylä/LIFE Revives project:
- Jouni Taskinen, +358403558094, jouni.k.taskinen@jyu.fi
- Heidi Kunttu, +358505890612, heidi.kunttu@jyu.fi
- Alleco Oy:
- Juha Syväranta, +358456393479, juha.syvaranta@alleco.fi
