I stood behind a worn shopping center outside of Crystal Springs, Florida, looking for the refuge where a hundred manatees were gathered for winter. I found them clustered in the emerald-colored spring, trying to enjoy a wedge of sunlight and avoid the hordes of people like me, boxing them in on kayaks and tour boats, leering over wooden decks. The nearby canals were lined with expensive homes and docks with jetskis. One manatee breached the water for a breath, and I could see the propeller scar on its back. 2018 was the second deadliest year on record for manatees. Like...