ROCKLAND — A new report on Maine’s 15 island communities shows that the islands’ population has increased about 6 percent since 1990.

The Rockland-based Island Institute’s “Island Indicators” report provides a detailed look at various indicators that affect Maine’s year-round island communities.

According to the report, the population grew by nearly 12 percent on Casco Bay islands and by a little over 5 percent on Penobscot Bay islands between 1990 and 2011, while falling by 8 percent on islands in eastern Maine.

The report further says that the median income on 11 of the 15 island communities is higher than the state as a whole. The higher incomes likely resulted from native and summer islanders earning a living elsewhere before returning to or settling on the islands.