When the steel claw of an excavator slashes into the berm of the Great Works Dam on Monday morning, it will mark the start of a multimillion-dollar project to allow endangered and dwindling species to return to their historic spawning grounds along Maine’s longest river, the Penobscot. When the project is done - scheduled for 2015, after an additional dam is razed and another bypassed - it will open access to 1,000 miles of habitat for the native fish, including endangered Atlantic salmon and short-nosed sturgeon that journey from the Gulf of Maine to breed in the cold, fresh waters...