A very rare fish is dying in the Florida Keys. Scientists are struggling to find out why

MIAMI — On a windy winter morning in January, Joyce Milelli was leading a kayak tour through the Lower Keys when the group rounded a mangrove island and encountered a startling sight: a rare, endangered sawfish, as big as Milelli’s paddleboard, wedged under a low clump of mangroves.

The discovery would set off alarms amid an ongoing mysterious fish disturbance, littering the scrubby islands between Key West and Big Pine with sick and dying fish.

“I knew right away something was not right,” said Milelli, a former nurse who grew up on Key Largo without ever seeing one of the rare sawfish. “I paddle all over the Lower Keys, all the way down to Dry Tortugas and the backcountry, where you don’t see many people paddling. My number one thing was to see a sawfish. So I knew this was really special, but why is it tucked under the branches?”

Five days later, the sawfish appeared again, this time flopping on a nearby shallow flat, where it quickly died.