Their large size, thick, tough skin, and lack of fins make it hard for predators to get a grip on them. Nonetheless, O'Shea suspects that a calf may be taken now and then by crocodiles or sharks. While manatees rarely have to grapple with reptile or fish predators, their leisurely lives of grazing are often interrupted by the fast-paced activities of humans. Boats pose a great danger to these shallow-water creatures. For example, in Florida and other places, many manatees bear the scars from close encounters with motorboats, whose slashing propellers lacerate the animals' hides.
Many manatees die from such encounters.
Native Americans hunted manatees for their flesh, bones, and hides. Early colonists used manatees' fat for lamp oil, bones for medicines, and hides for leather. Today, manatee hunting has all but ceased in the United States, but continues in the Caribbean, West Africa, and Central and South America, where in some areas a tradition of eating manatees apparently dates back to the Catholic conquistadors, who called manatees fish so they could be eaten during Lent. Conservationists believe this practice is now dying out. Some hunters have changed their ways in order to cash in on ecotourism.