A new record of the freshwater pearl mussel Margaritifera margaritifera L. (Bivalvia,Unionoida) from the River Narcea (Asturias,north‐western Spain)

1. A population of the freshwater pearl mussel Margaritifera margaritifera L. was found in the River Narcea in the province of Asturias (north‐western Spain). Primary analysis of the population shows that it is well distributed along the river and is particularly abundant in shady river banks with a gravel substrate. 2. The length of living mussels ranges between a minimum of 22 mm and a maximum of 116 mm, with most in the size class between 65 mm and 70 mm. There is a good proportion of young mussels, although no fertile females were found in the course of the investigation. 3. Although there is no specific legislation in Spain for the protection of M. margaritifera, it has recently been proposed to include M. margaritifera in the Spanish List of Threatened Species as ‘vulnerable’. 4. Although the River Narcea seems to provide suitable conditions for the pearl mussel (water quality, available salmonid hosts, etc.), the main conservation measures must be directed at avoiding river fragmentation from dams, channelization and organic enrichment from individual farms or towns situated close to the river bank. Copyright © 2000 John Wiley & Sons, Ltd.