A gray seal, Kiwi, found stranded on Nantucket in January was successfully released back into the ocean on Thursday after being cared for at Mystic Aquarium’s Animal Rescue Clinic. Kiwi was malnourished and had an infection when rescued, but after nearly doubling her weight while recovering, she was released at Blue Shutters Beach in Charlestown, where onlookers cheered her return to the sea.