This half-hour documentary about Smith Island, MD, features Mary Ada and Dwight Marshall, whose lives personify the Chesapeake Bay’s seafood-harvesting culture and history, and their four children, who chose to break with that tradition. The film, like Tom Horton’s 1996 book of the same name, is both a celebration and elegy for a place beset with erosion, dwindling population, and vanishing economic opportunities.