Acta Univ Latv (2005) 691: 121–128

Assessment of the condition of freshwater pearl mussel Margaritifera margaritifera (Linnaeus 1758) populations in Latvia

Abstract

The freshwater pearl mussel Margaritifera margaritifera is a species threatened throughout the world. Pear mussel populations in Latvia were assessed using criteria developed in Sweden. The population size, distribution and density of the four largest Margaritifera margaritifera populations in four rivers were determined. For the estimation of pearl mussel population age structure, classes of mussel shell length were used. The most important threat was from dams and other beaver activities, which decreased the viability of the pearl mussel population. Two of the pearl mussel populations of Latvia, according to the Swedish scoring system, correspond to class II with a high nature conservation value, five populations to class I with a lower nature conservation value, and none to the class III, a very high nature conservation value.