A sheen appears, Dec. 24, 2020, south of Yabucoa, Puerto Rico. (U.S. Coast Guard photo) SAN JUAN, Puerto Rico — The Coast Guard responded to a marine casualty Thursday south of Puerto Rico. Sector San Juan watchstanders received a mayday call from the 112-foot tugboat Proassist III crew stating they were taking on water with three people aboard approximately two miles south of Yabucoa Harbor, Puerto...