Assessment of the population genetic structure of Sphyrna lewini to identify conservation units in the Mexican Pacific

Abstract

Due to the current status of the scalloped hammerhead shark (Sphyrna lewini) as a threatened species, the assessment of genetic diversity, divergence, and demographic parameters of populations in the eastern Pacific Ocean may assist in developing appropriate strategies for sustainable fisheries and species conservation. We analyzed samples collected from 2001 to 2003 from seven locations in the Mexican Pacific Ocean and two in the southwestern Gulf of Mexico, using single-stranded conformation polymorphism of a mitochondrial control region fragment and five microsatellite loci. The mitochondrial data did not show population divergence among locations from the Mexican Pacific Ocean; however, the microsatellite data showed a divergent population in Baja California. Additional differences were also observed between the northern and central locations of the Mexican Pacific. The historical demography analysis revealed spatial expansion events, possibly related to glacial-interglacial cycles that occurred approximately 450,000 years ago. The divergence found should be considered in the formulation of fisheries management and conservation policies of the species in the region.