How can the Freshwater Pearl Mussel's (Margaritifera margaritifera) Situation Become Better in Lekhyttan

Abstract This study takes up a local issue in the village of Lekhyttan, where Johan Molin is concerned about the freshwater pearl mussels (Margaritifera margaritifera) situation. He is a landowner and wonders what the situation is for the mussels and what he himself possibly can do, to hopefully improve their situation. This paper looks at the different aspects on why the mussels are distributed as they are in the stream and trying to understand why new recruitment is poor in the Lekhyttan Stream. Dividing the area into two zones, east (that has a population of mussels) and west (which has none), makes it easier to analyse which type of habitat they prefer. Why the mussels can be found in one zone and not in the other can be due to several different factors. The factors investigated were: 1) bottom structure, 2) trout (Salmo trutta) - spawning area and mature trout habitat as the trout play an important role in the mussels lifecycle, 3) surrounding vegetation, 4) predation from signal crayfish (Pacifastacus leniusculus) and 5) water quality checked with a pH and iron test – from the inflows of ditches and pipes. There was a significant difference between the two zones in the bottom sediment structure: the west zone had a high percentage of stone, whilst the east zone consisted of finer materials and had far more suitable habitat areas for the trout (both in spawning as well as for larger trout). Tests from the inflowing water in the west zone had water with low and high pH levels, as well as high iron contents. These inflows need to be fixed with a pond and reed filtration bed, as well as a recommendation on cutting back the number of crayfish that can be a potential threat to juvenile mussels. Following these recommendations will hopefully improve the situation locally for the Lekhyttan freshwater pearl mussel and maybe even lead to new recruitment