Defining demographically independent units and understanding gene flow between
them is essential for managing and conserving exploited populations. The scalloped
hammerhead shark, Sphyrna lewini , is a coastal semi-oceanic species found
worldwide in tropical and subtropical waters. Pregnant females give birth in shallow
coastal estuarine habitats that serve as nursery grounds for neonates and small
juveniles, and adults move offshore and become highly migratory. We evaluated the
population structure and connectivity of S. lewini in coastal areas across the Eastern
Tropical Pacific (ETP) using both sequences of the mitochondrial DNA control region
(mtCR) and nuclear-encoded microsatellite loci. The mtCR defined two genetically
discrete geographic groups: the Mexican Pacific and the central-southern Eastern
Tropical Pacific (Guatemala, Costa Rica, Panamá, and Colombia). Overall, the mtCR
data showed low levels of haplotype diversity ranged from 0.000 to 0.608, while
nucleotide diversity ranged from 0.000 to 0.0015. A more fine-grade population
structure analysis was detected using microsatellite loci where Guatemala, Costa Rica,
and Panamá differed significantly. Genetic diversity analysis with nuclear markers
revealed an observed heterozygosity ranging from 0.68 to 0.71 and an allelic richness
from 5.89 to 7.00. Relatedness analysis revealed that individuals within nursery areas
were more closely related than expected by chance, suggesting that S. lewini may
exhibit reproductive philopatric behaviour within the ETP. Findings of at least two
different management units, and evidence of philopatric behaviour call for intensive
conservation actions for this critically endangered species in the ETP.Universidad de Costa Rica/[801-B6-214]/UCR/Costa RicaNational Secretary of Science and Technology/[FID-156]/SENACYT/EcuadorThe Phoenix Zoo/[no.33297]//Estados UnidosPADI Foundation/[no.32809]//Estados UnidosRufford Foundation/[no.22366-1]//Reino UnidosWaitt Foundation/[no.33297]//Estados UnidosFundación Reserva Ojochal/[]//Costa RicaThe Whitley Fund for Nature/[]/WFN/Reino UnidoSandler Family Foundation/[]//Estados UnidosOsa Conservation/[]//Costa RicaUCR::Vicerrectoría de Docencia::Ciencias Básicas::Facultad de Ciencias::Escuela de BiologíaUCR::Vicerrectoría de Investigación::Unidades de Investigación::Ciencias Básicas::Centro de Investigación en Biología Celular y Molecular (CIBCM)UCR::Vicerrectoría de Investigación::Unidades de Investigación::Ciencias Básicas::Centro de Investigación en Ciencias del Mar y Limnología (CIMAR