Federal regulators have listed the Atlantic salmon in the Penobscot, Kennebec and An-droscoggin rivers as an endangered species. Will this affect the pulp and paper businesses that still rely on the rivers and the hydropower industry? Will the federal listing hurt the state’s economy in other ways? Or is the listing an important step to protect one of Maine’s signature species, perhaps heralding the beginning of a revival of the fish in the state’s biggest rivers?