As the boat cruised around Treat Island, 45 passengers shuffled around the deck to get a good view of the isle’s evergreen-covered hills, gravel beaches and open meadows. Located off the coast of Eastport, the 71-acre island, conserved by the Maine Coast Heritage Trust, was one of the first stops on the recent MCHT tour of Cobscook Bay. “It was once owned by Upham Treat, who caught herring in weirs and smoked them,” MCHT regional steward Deirdre Whitehead said as she stood at the stern of the boat with a microphone.