Meeting Abstract
In sharks, the skin acts as an exotendon, controlled by internal muscular pressures produced during extension and relaxation enhancing body stiffness during swimming. The surface of shark skin is covered with denticles which have drag-reducing properties thought to increase swimming speeds in some species. Dermal denticle morphology has been shown to vary regionally along the body and correlate with swimming performance across species. Our goal is to assess regional differences in denticle density and skin tensile properties in four coastal species of shark (Carcharinus limbatus, Carcharinus leucas, Sphyrna tiburo, Sphyrna lewini). We hypothesized that the denticle density and tensile strength (MPa), stiffness (MPa), and toughness of skin (Jm3) would vary regionally along the body of an individual and among species. Juveniles from each species were obtained and skin was dissected from the underlying fascia and muscle at 10 anatomical landmarks. An hourglass-shaped punch was used to extract the skin samples in a cranial to caudal orientation. Denticle density was counted using a dissecting microscope. Denticle density varied significantly among both regions and species, and showed a significant species region interaction. Skin samples were tested in tension at a strain rate of 2 mm/sec until failure on an Instron testing system using a 2kN load cell. A stress strain curve was generated for each sample and tensile properties were calculated. We found significant species and region effects for all three tensile properties. We also found a species by region interaction for stiffness.
