Follow the Light
In my experience, the best location near Acadia National Park on Mount Desert Island to capture images of an actual working fishing harbor is in the village of Bass Harbor, part of the municipality of Tremont. There are two sides to be aware of. Bass Harbor is on the eastern side whereas, Bernard, is on the western side. You should try both sides, especially when considering the time of day as the angle of light and its direction will make a big difference here. The opening to the sea and the harbor itself faces South.