As the seaplane soared more than 1,000 feet in the air, I scoured the crystalline waters below, hoping for a glimpse of dolphin squadrons, manatees, perhaps sharks. They might be visible even at this altitude, I’d been told. I saw none. Yet among several seemingly motionless sailboats, a shadowy yet distinct shape stood out. It was the shipwreck of the Arbutus, a treasure-hunting vessel that sank in 1983. The haunting, rather morose, image was set against an otherwise celestial landscape.