An attempt was made in October 1988 to more accurately estimate the population of monk seals Monachus monachus living along the western coast of the Cap Blanc peninsula, Mauritania. Seals were only observed close to three of the four caves shown on figure 1. We were able for the first time to enter two of these caves (1 and 3) from the sea, but failed to do so for cave 4 : however, we ascertained that cave 4 also harboured some seals. No seals were observed elsewhere along the penisula in 1988, except at its very tip, where 5 large individuals appear to be resident in the small Nature Reserve of Cap Blanc. The Monk seal population of the peninsula can be presently estimated at 1 30 individuals at least. It has apparently remained stable over the last ten years. The percentage of young individuals in the sample observed was of ca 20-27 % . This population is seriously threatened by the activities of an ever increasing number of both local fishermen and offshore trawlers.