CLIFTON, K.B.*; GOLDEN, J.A.; REEP, R.L.; University of Florida, Gainesville; University of Florida, Gainesville; University of Florida, Gainesville: Material Properties of Subadult Manatee Bone

Watercraft-related mortality of the Florida manatee accounts for 24% of all deaths from 1976-2002. Reducing this mortality is identified as a high priority in the manatee recovery plan. A first step to improve the understanding of biological effects of boat strikes is to understand the material properties of manatee bone. This study investigated the material properties of subadult manatee bone. Subadults were chosen because the majority of mineralization occurs in this age class, as their skeletons are still developing, they best illustrate the processes responsible for the development of their unique, pachyostotic bones. Flexural strength, toughness, and Young’s Modulus were measured for six male and six female subadults. Parallelpipeds were machined from ribs in the anterior, middle, and posterior body regions, and fractured in three-point bending. Fractographic analysis of fracture surfaces was used to calculate toughness. Mean flexural strength by animal ranged from 91-163 MPa, mean toughness from 1.9-2.9 MPa�m^1/2, and mean Modulus from 8-15 GPa. Material properties increased with body size up to 265 cm total length, then declined with increasing body size. Females were significantly higher than males for all variables. In comparison, typical flexural strengths for human and bovine bone tested in 3-point bending are 209 MPa and 224 MPa, respectively. Toughness of human and bovine bone ranges from 2.2-6.3 MPa�m^1/2, indicating that manatee bone is on average less strong and tough (i.e. fractures more easily). Material properties are likely correlated to mineral content and microstructure. Furthermore, the decrease in material properties in animals larger than 265 cm may mark the start of hypermineralization characteristic of their pachyostotic bone.