Molecular and morphological evaluation of the bonnethead shark complex Sphyrna tiburo (Carcharhiniformes: Sphyrnidae).

The bonnethead Sphyrna tiburo is a wide-spread, small species of coastal hammerhead shark with a long history of taxonomic uncertainty, including, according to some authors, disjoint subspecies in the western Atlantic and eastern Pacific oceans. The present study investigates the level of morphometric and genetic variation within the Sphyrna tiburo complex throughout most of its distributional range including the western Atlantic, the Gulf of Mexico, the Caribbean, and the eastern Pacific. A morphometric study, including a comparison of ampullary densities, and a molecular analysis of two mitochondrial genes, was performed. We analyzed variation in cephalofoil shape between and within lineages, based on landmarks and Fourier analysis of the silhouettes. All tests delineated discrete morphological groups, including differences of ampullae density for those lineages in which this information could be unambiguously assessed. Both morphometric and molecular analysis support the existence of three different evolutionarily significant units (two in the Atlantic: one northern and one south-central, and a third in the eastern Pacific) that deserve specific taxonomic status. We urge a deep taxonomic review of this complex to gather biological data on each lineage and develop adequate independent conservation strategies and actions to protect the various evolutionary units. [ABSTRACT FROM AUTHOR]