Background knowledge and status of the freshwater pearl mussel Margaritifera margaritifera in the county of Aust-Agder, Norway

Sammendrag

This report puts together knowledge about the freshwater pearl mussel in the county of Aust-Agder, regarding history and current status. The oldest information about the river pearl mussel in the county is found among the answers to a survey from 1743, conducted by the “Danish Chancery”. From the answers, we found reports of localities with pearl mussels in Froland and Vegårshei. Bishop Pontoppidan in 1753 mentions two localities with mussels in the county, ”Baaselands Pitch” and the until now unknown ”Berge-River”. The latter is to day known as the River Storelva in the watercourse Vegårvassdraget. An article in the newspaper Agderposten from 1937 describes the pearl fisheries in the River Storelva in 1910. One person had an income of NOK 200 that summer, which corresponds to NOK 11 730 per September 2013. In 1967 it is stated that there had been ”fished” ”many pearl oysters” in the River Storelva downstream the waterfall at Fosstveit. In about 12% of the sites in Aust-Agder there are still remnant populations of the freshwater pearl mussel. It is registered about 1/3 more sites with pearl mussels in the county than what has been known until now. Most of these sites are located in the eastern parts of the county, near the coastline. In 2010 it was confirmed that there are still pearl mussels in River Storelva (Vegårvassdraget) below the waterfall at Fosstveit. In Lilleelv in Øyestad it was registered several relatively young individuals of the freshwater pearl mussel, which shows that recruitment is taking place. In the Vassbotn stream in Birkenes the pearl mussel seems to be declining in numbers. The largest and most viable population of the freshwater pearl mussel in Aust-Agder is found in Hammertjennbekken in Risør.