Much as the sirens of Greek mythology were said to mesmerize sailors, the family of gentle sea creatures known as Sirenia—manatees and dugongs—captivated photographer Jason Gulley as he spent months documenting Florida manatees for the story in the January issue of National Geographic.

Unlike the much-loved manatee in the Sunshine State, little is known about the two other species and the dugong, a cousin found in coastal waters from East Africa to Australia. The International Union for Conservation of Species lists all four as vulnerable, in part because of hunting and degradation of their waters.

“What we know about Florida manatees is thanks to the fact that they congregate in water that