The 3,100ha mangrove swamp in the park is a relict of a previous humid geological period when Banc d'Arguin was a vast estuary mouth for rivers flowing from the Sahara. Rainfall is irregular and very low with an average of 34mm-40mm per year. Land mammals include Dorcas gazelle, jackal, fennec, sand fox and hyenas. Marine mammals regularly recorded include several whale and dolphin species and monk seals. Four species of turtle frequent the area.
Fish are one of the most important components of the fauna.
The shallow tidal flats act as important breeding and nursery areas. The local people, the Imraguen or Amrig, relate many of their customs to the natural environment. Even their name literally means 'the ones who gather life'. Imraguen tribesmen still maintain their age-old life styles, based almost exclusively on harvesting the migratory fish populations using traditional sailing boats. Fishing techniques include the unique symbiotic collaboration with wild dolphins to catch schools of grey mullet.