PROVIDENCE, R.I. — Areas of upper Narragansett Bay that have been off-limits to shellfishing for 70 years will reopen this weekend due to cleaner water, the Rhode Island Department of Environmental Management announced Friday afternoon.The relaxation of restrictions, which include the lifting of closures in Cormorant Cove, Block Island, and the elimination of a seasonal closure for Greenwich Bay, will take effect at sunrise on Saturday, according to a news release issued by DEM.