I saw a trip report on cloudbirders.com which included a sighting of Mediterranean Monk Seal in Mauritania. I emailed the author (Hans Meltofte) for further details, and he replied:
Yes, it was on Cap Banc, where a large male has been stationary for quite some time, but sometimes away from the cape on feeding excursions, of course.
It’s apparently part of a population of “a few hundred individuals” on the coast of West Sahara; inaccessible due to mines, we were told.
Cap Blanc is freely accessible with a 4WD from Nouadhibou; less than one hour’s driving in fact. There’s even an information center for the national park there, including a park ranger that has to be contacted in advance, if you want to see the exhibition.