The Bissagos Islands, also spelled Bijagós (), are a group of about 88 islands and islets located in the Atlantic Ocean off the coast of Guinea-Bissau. The archipelago was formed from the ancient delta of the Geba and Grande de Buba rivers and spans an area of . 20 of its islands are populated year-round, including the most populated island, Bubaque, where the administrative capital is situated. There is a high diversity of ecosystems: mangroves with intertidal zones, palm forests, dry and semi-dry forests, secondary and degraded forests, coastal savanna, sand banks and aquatic zones. The archipelago was declared a UNESCO Biosphere Reserve in 1996. Demographics The population is estimated at about 30,000 (2006) and the ethnic group Bissago () predominates. It has a relatively youthful population due to high birth rates and low life expectancy. Economy The economy is largely rural, with many families living from subsistence farming and fishing. There is some tourist activity, mostly boat charters from neighboring Senegal. Lack of infrastructure and communication links prevent the development of the islands' tourism potential. Starting in the early 2000s, several of the islands began to be used as transit depots for narcotraffic, which is quickly changing the social and economic fabric of the islands. History In pre-European colonial times, the islands were central to the trade along the coast of West Africa and they built up a powerful navy. In 1535, this enabled them to rout the Portuguese, who later built a fort on Bissao, which was abandoned in 1703. The islands were not formally annexed by Portugal until 1936. The Bissagos were visited by Austrian anthropologist and photographer Hugo Bernatzik in 1930–1931, who documented daily life among the Bidyogo people. The London School of Hygiene and Tropical Medicine is conducting research into infectious diseases on the islands. Because they are so isolated there is less danger of contamination of the results than in other places. Culture Due to difficulties of communication with mainland Guinea-Bissau that persist to this day, the population has a considerable degree of autonomy and has shielded its ancestral culture from outside influence. The Bijago language is spoken along with Portuguese and creole. Some authors argue that Bijago culture tends to be matriarchal, with women managing the household, the economy, law, as well as initiating courtship (women choose their husbands and terminate the matrimony). Other sources dispute this and suggest that closer examination has