From Wikipedia: https://en.wikipedia.org/wiki/Mafia_Island
Mafia Island ("Chole Shamba") is part of the Tanzanian Zanzibar Archipelago, together with Unguja, Pemba and Latham Island. As one of the six districts of the Pwani Region, Mafia Island is governed from the mainland, not from the semi-autonomous region of Zanzibar, of which it has never been considered to be a part politically.
According to the 2002 Tanzania census, the population of the Mafia District was 40,801. The economy is based on fishing, subsistence agriculture and the market in Kilindoni. The island attracts some tourists, mainly adventure scuba divers, game fishermen, and people wanting relaxation.