Abaco and Cays (ăb`əkō, kēz, kāz), island group, c.780 sq mi (2,020 sq km), most northerly of the Bahamas. It includes Great Abaco (the largest), Little Abaco, and the surrounding cays. The low islands, composed mainly of coral limestone, have native pine forests. Fish and sponges are taken from surrounding waters. Great Abaco was settled by Loyalists from New York City in 1783.