Koyun Island  Koyun Island (, literally "Sheep Island") is a Turkish island in the Sea of Marmara. At it is a part of Erdek ilçe (district) of Balıkesir Province. It is situated between the better known islands of Avşa Island and Paşalimanı Island. The island is a long island from north to south. Its total area is about . There are only a few summer houses on the otherwise uninhabited island.