摘要：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. Th e populationsize, distribution and density of the four largest Margaritifera margaritifera populations in four riverswere determined. For the estimation of pearl mussel population age structure, classes of mussel shelllength were used. Th e most important threat was from dams and other beaver activities, whichdecreased 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 conservationvalue, fi ve populations to class I with a lower nature conservation value, and none to the class III, avery high nature conservation value.
关键词：conservation value; Margaritifera margaritifera; Latvia; population age structure.
