The U.S. Coast Guard and several state and local agencies are working to salvage a 42-foot fishing boat that sank at its mooring in Stonington harbor Friday. Dave Lebrecht, Coast Guard spokesman, said the sinking was reported at 1:30 p.m. The boat was carrying about 700 gallons of fuel and there was some fuel leakage spotted Friday but none since then. The Coast Guard, Maine Marine Patrol, the Stonington harbor master, the Department of Environmental Protection and a number of fishermen were on the scene Saturday trying to raise the boat from about 70 feet of water. The cause of the sinking has not been determined but foul play is not believed to be involved, said Lebrecht.