Shape analysis of shark jaws as a tool to identify species involved in incidents with humans

Shark incidents in Recife, Pernambuco state (Brazil), are registered since 1992. The occurrence of those events is in a relatively small area of urban beaches of about 30 km long, making up one of the world's highest indices of shark incidents per unit of area, totaling 64 casualties, of these 24 were fatal. To mitigate shark incidents, the knowledge on shark species involved is crucial given that each species has specific usage of the habitat and dissimilar feeding strategy. Jaws of five species caught along the Pernambuco coast (Brazil), corresponded to 2 specimens of Carcharhinus acronotus, 4 specimens of C. leucas, 1 of C. limbatus, 4 of Galeocerdo curvier and 3 of Sphyrna lewini. Relative Warps Analysis was applied to enhance possible differences among jaw shapes of the studied species. The consensus configuration from the 14 images was obtained. The first two relative warps components explained 70.17% of the total observed variation. Four distinct groups were clearly observed. Three groups were formed by single species, corresponding to G. curvier, C. leucas and S. lewini, respectively, and one group formed by the combination of C. acronotus and C. limbatus. As expected, due to its peculiar skull shape, S. lewini jaws are very different from other analyzed species, thus all observed individuals of this group were found isolated from the others, considering the horizontal axis. Relative warps and curvature analyses show to be useful tools in the forensic study of shark incidents. In general, jaws shape significantly differed among species.