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Study Shows Manatees Have Brittle Bones

March 18, 2005

GAINESVILLE, Fla. (AP) _ Despite their huge size, the bones of manatees are as brittle as fine porcelain, making them extremely vulnerable to being broken when struck by a boat, a University of Florida researchers said Thursday.

The surprising findings could ultimately change public policy for the management of Florida’s waterways, said Roger Reep, a professor of the UF College of Veterinary Medicine’s physiological sciences department.

``When you pick up a manatee rib, it’s much denser than a cow bone or human bone. Most people would think these ribs would be really strong, as they’re so heavy. But in fact, they behave like ceramic material,″ Reep said.

The bones of the endangered sea cows have no marrow cavity, which is why their bones are so dense. But that density makes them more fragile.

Additional studies from the ongoing project, which mingles veterinary physiology and engineering expertise in a first-ever effort to describe the biomechanics of impact injuries, will be published in an upcoming issue of the Journal of Biomechanics.

The researchers are using an air gun to hurl a 2-by-4-inch board toward a manatee bone target to reconstruct the ways various forces are distributed through the bone.

``What we are doing is getting an idea of the amount of energy it takes to break a bone,″ said Reep, who has teamed with Jack Mecholsky, associate chairman of the department of materials sciences and engineering at UF’s College of Engineering. They are working with UF graduate student Kari Clifton on the project, which was part of her dissertation research in 1998 with funding from UF’s Marine Mammal Medicine Program.

The force applied by a boat to a manatee depends primarily on boat speed and the size of a boat, Reep said.

``One thing we’re not sure about yet is how much of force of the boat actually reaches the ribs, since manatees don’t get hit directly on the ribs, but rather on the soft tissue covering the ribs,″ Reep said.

Only about 3,000 manatees remain in the wild, with most of them concentrated in Florida, but have been spotted as far west as Texas and as far north as Virginia.

Manatees have been listed as an endangered species since 1967. They are slow-gentle mammals that are entirely aquatic. Human activities are the major threat to their survival through boat-related injuries and deaths, habitat loss or degradation.

From 1974 to 2004, 5,329 manatee deaths were reported in Florida, of which 1,164 were attributed to watercraft collisions, according to the Florida Fish and Wildlife Conservation Commission.

Patti Thompson, director of science and conservation for the Maitland, Fla.-based Save the Manatee Club, said reducing the watercraft collisions is the best means to reduce deaths and increase the manatee’s survival.

``It’s a surprising outcome of UF’s research that their bones are much more fragile than anyone expected,″ Thomas said.

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