Abstract
The pearl mussel was abundant in the Sudety Mountains until the late 19th century. No live mussels were found within the present borders of Poland since the early 20th century. In 2006–2007 we did a detailed survey of 50 streams and rivers within the former range of the pearl mussel to verify its current status and assess the habitat conditions. No live mussels were found. On the whole, the rivers and streams were found to be degraded. Only four streams met the habitat requirements of the species. Well-preserved shells with a nacre layer were found at the site of the last known population in the Koci Potok stream. To determine whether the shells represented an extinct population or rather indicated the presence of the last survivors, we placed Unio crassus shells in the stream within the historical range of occurrence. Those shells dissolved at the rate of approximately 20% per year, indicating that empty shells would not have remained intact within the channel. Possibly the earlier-found shells had been preserved in the banks above the water level. The possibility that they represent the last survivors can not be excluded. Further search for the last survivors, extended to cover northern Poland, is recommended. KEy wORDS: Margaritifera margaritifera, shell dissolution, stream survey, oligotrophic water, Allee effect
Highlights
The insufficiency of data on the distribution and population health of European freshwater mussels is one of the main obstacles to their conservation (Lopes-Lima et al 2014)
We searched mainly for streams similar to the “A” river in Szumawa, Czech Republic, site of the nearest pearl mussel population; the landscape and habitat features there are similar to those in Łużyce, where the largest populations of M. margaritifera in the Sudety Mts were found in the past
Most of the upper sections of the streams and rivers that formerly had viable pearl mussel populations are completely regulated, running along geometric beds sided with stone walls (e.g. Potok Miłoszowski stream)
Summary
The insufficiency of data on the distribution and population health of European freshwater mussels is one of the main obstacles to their conservation (Lopes-Lima et al 2014). There are numerous studies on its genetics, distribution and biology (Geist 2010). Its range spans the northern part of the European continent from Spain and Portugal to Finland and the adjacent part of Russia, its distribution range is disjunct in Poland and Lithuania where the species has gone extinct (Lopes-Lima et al 2014). This mussel has a very long lifespan (Dunca et al 2011). The extinction process of the species has not been studied in Poland, and the information existing elsewhere is sparse and published in national languages
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