Manatees belong to the scientific order of Sirenia, of which there are only four species remaining in the world: West Indian, West African, and Amazonian manatees, and dugongs.
All four species are vulnerable to extinction from habitat loss and other impacts related to human population growth and coastal development.
According to Self-Sullivan, the wholesale slaughter of manatees during the 17th and 18th centuries to feed plantation workers in the Caribbean contributed to their drastic decline.
By the early 1900s manatees were commercially extinct.
"There were no longer enough around to make it worthwhile to hunt manatee," she said.
Today, manatee hunting is illegal almost everywhere in the world, though they are still taken in many places in West Africa and Central and South America, Self-Sullivan says.
In the African country of Ghana, where Self-Sullivan advises a manatee conservation project, the marine mammals are killed "for subsistence," she said.
"People in the villages are obviously having a hard time getting enough food and quality protein."
In other regions, such as the Chetumal Bay bordering Mexico and Belize and the Bay of Honduras that encompasses the coasts of Belize, Honduras, and Guatemala, manatees are thought to be hunted and sold on the black market. (See Belize map.)
In Florida and Belize, boats are the greatest manatee threat.
Almost every adult manatee examined in Florida's waters bears at least one scar from a collision, according to Self-Sullivan.
"It's a matter of shared habitat," she said. "Primary [manatee] habitat is shallow coastal waters, and that's where most of the boats are, the small boats in particular."
Manatee-boat collisions also happen in Belize, Self-Sullivan says, but the impacts are less frequent and less lethal there.
This may be because manatees can hear boats approaching in the channels and lay on the bottom for the boats to pass before coming up to breathe.
However, the giant sea mammals are unable to hear boats that cut across the sea-grass beds because the beds muffle motor noise.
"They can't hear it until it's right on top of them, and then it's startled and as likely to bolt in the direction [of the boat] as away from the boat," she said.
Tour-operator education programs like the one run by Wildlife Trust teach guides not to cut across the beds, thereby reducing manatee collisions.
Auil of the Wildlife Trust says the Belizean government is working with her organization and other conservation groups to post boat speed limit signs in key manatee areas. She now hopes the rules will be enforced.
"If no one is on the water to enforce the signs, boaters may ignore them," she said. "The success is yet to be seen, but we are hopeful they will comply."
Free Email News Updates
Best Online Newsletter, 2006 Codie Awards
Sign up for our Inside National Geographic newsletter. Every two weeks we'll send you our top stories and pictures (see sample).
SOURCES AND RELATED WEB SITES