2017

The Rare Freshwater Pearl Mussel has been Found in the Rivers of Latvia's State Forests

Upon surveying a river in Vidzeme, Mārtiņš Kalniņš, JSC "Latvia's State Forests" (LVM) Environmental Expert, found six living freshwater pearl mussels, as well as several empty shells. According to the Environmental Expert, earlier there were many of these mussels to be found in the rivers of Latvia, but for various reasons they have died out.

The freshwater pearl mussel (Margaritifera margaritifera L.) is the rarest animal that can be spotted in Latvia's rivers. Researchers noticed ageing of the population of these animals already in the thirties of the last century. Today, the freshwater pearl mussel has been included not only in all lists of protected species in Latvia, but also in Appendix III to Bern Convention.

"One of the reasons why the freshwater pearl mussel population in Latvia has shrunk is the activity of beavers. Animal-made dams and river bumps disturb freshwater pearl mussels, because they need cool, running and oxygen-rich water, as well as a riverbed covered with gravel and pebbles. Equally disturbing is the formation of driftwood - it, like beaver-made dams, form river sections unsuitable for living. Already for several years, JSC "Latvia's State Forests" has been maintaining the surveyed river section free from beaver dams, periodically performing partial removal of fallen trees and debris", says Mārtiņš Kalniņš.

Not only the growing environment, but also the fish that are found in oligotrophic rivers - salmon and brook trout - are important for the development of freshwater pearl mussel larvae (glohidium). Mussel larvae spend a short period of time living on gills, without causing any damage at the same time.

Historically, pearl picking has also contributed to the extinction of freshwater pearl mussels. The currently small groups of freshwater pearl mussels have once been huge colonies, from which white pearls were harvested to the royal palaces of Sweden and Russia. As time and fashion changed, people started to demand larger and better quality pearls that do not occur in rivers of Latvia or Europe.

The endangered freshwater pearl mussel belongs to the Bivalvia mollusc class, Mollusca mollusc type. Its body is covered by a rectangular two-piece shell. The surface of the shell itself is black, but the inside of it is covered with a white pearl shell. At the front of the body of the freshwater pearl mussel there is a leg that is used by the animal to move and, if necessary, to dig into the sand.

In Europe, this species of bivalve molluscs has survived only in mountainous areas, but is no longer present in the vicinity of agricultural land or inhabited areas. There are several freshwater pearl mussel deposits in Latvia - in river basins with many forests in the area.