A majority of the population of Mauritania depends on agriculture and livestock for a livelihood, even though most of the nomads and many subsistence farmers were forced into the cities by recurrent droughts in the 1970s and 1980s. Mauritania has extensive deposits of iron ore, which account for almost 50% of total exports. The decline in world demand for this ore, however, has led to cutbacks in production. With the current rise in metal prices, gold and copper mining companies are opening mines in the interior. The nation's coastal waters are among the richest fishing areas in the world, but overexploitation by foreigners threatens this key source of revenue. The country's first deep water port opened near Nouakchott in 1986. In recent years, drought and economic mismanagement have resulted in a buildup of foreign debt. In March 1999, the government signed an agreement with a joint World Bank-International Monetary Fund mission on a $54 million enhanced structural adjustment facility (ESAF).