摘要：The population of freshwater pearl mussel Margaritifera margaritifera in the river Pēr.upe, known for pearl fishing till the beginning of the 20 th century, was monitored during the period 1999 to 2010. The area is currently designated as a Natura 2000 site. Measurements of non-living shells showed that the proportion of small individuals in the population has been decreasing and that population ageing has occurred during the last years. Data on water quality indicated that the nitrogen and phosphorus concentrations are considerably higher compared to the optimum level. In addition, there are some problems with beaver dams and bad overall quality of the environment. The population will potentially recover if the river ecosystem improves
关键词：age structure; Latvia; Margaritifera margaritifera; monitoring; non-living population; pearl mussel
