Banc d'Arguin is the stretch of Mauritanian coast where the Sahara runs straight into the Atlantic, twelve thousand square kilometres of tidal flats, sandbanks and dune islands. The banks stay shallow for tens of kilometres out, and cold water welling up from the deep meets sun-warmed shallows over them, which makes this one of the richest fish nurseries anywhere. Everything you find here eats from that. Each winter around two million waders come down off their Arctic breeding grounds and pack the flats, more than two-thirds of all the bar-tailed godwits on Earth among them. Flamingos and pelicans work the water, and West Africa's largest seabird colonies are on the islands. Twice a day the tide redraws the whole bank, uncovering pale sand islands and braided channels that are gone again by the next high water. At low tide around Tidra you can walk out onto kilometres of firm sand and shallow channels where the flocks are feeding, and from a dune crest at Cap Tafarit you can read the pattern whole.
The Imraguen, the fishing people of this shore, work the banks in broad wooden lanches under sail, the only boats allowed out there and often the only way you get into the inner channels. When the mullet run down the coast from late October into January, the men wade in and slap the surface with sticks. Atlantic humpback dolphins answer by driving the shoal toward the shallows, the nets close around it, and both sides take their share. Only a handful of working partnerships between people and wild dolphins have ever been recorded anywhere. Ashore, nothing from the catch is thrown out. The flesh is dried, the heads and organs are boiled down into a vitamin-rich oil called dhên, and the roe of the pregnant fish is salted and sun-dried by the women into bottarga, sold far beyond Mauritania. Low mounds of shells lie along this coast, the leavings of camps that cleaned their catch on the same spots the boats still sail from.