DOI: 10.5061/dryad.7m0cfxpzr
title: Genetic population dynamics of the critically endangered scalloped hammerhead shark (Sphyrna lewini) in the Eastern Tropical Pacific

description: The scalloped hammerhead shark, Sphyrna lewini, is a Critically
 Endangered, migratory species known for its tendency to form iconic and
 visually spectacular large aggregations. Herein, we investigated the
 population genetic dynamics of the scalloped hammerhead across much of its
 distribution in the Eastern Tropical Pacific (ETP), ranging from Costa
 Rica to Ecuador, focusing on young‐of‐the‐year animals from putative
 coastal nursery areas and adult females from seasonal aggregations that
 form in the northern Galápagos Islands. Nuclear microsatellites and
 partial mitochondrial control region sequences showed little evidence of
 population structure, suggesting that scalloped hammerheads in this ETP
 region comprise a single genetic stock. Galápagos aggregations of adults
 were not comprised of related individuals, suggesting that kinship does
 not play a role in the formation of the repeated, annual gatherings at
 these remote offshore locations. Despite high levels of fisheries
 exploitation of this species in the ETP, the adult scalloped hammerheads
 here showed greater genetic diversity compared with adult conspecifics
 from other parts of the species' global distribution. A
 phylogeographic analysis of available, globally sourced, mitochondrial
 control region sequence data (n = 1,818 sequences) revealed that scalloped
 hammerheads comprise three distinct matrilines corresponding to the three
 major world ocean basins, highlighting the need for conservation of these
 evolutionarily unique lineages. This study provides the first view of the
 genetic properties of a scalloped hammerhead aggregation, and the largest
 sample size‐based investigation of population structure and phylogeography
 of this species in the ETP to date.
description: Scalloped hammerhead shark samples were genotyped at 9
 microsatellite loci including five loci from <em>Sphyrna</em>
 <em>lewini</em> (SLE027, SLE033, SLE045, SLE038, SLE089)
 previously described by Nance et al. (2009) and four loci isolated in
 other shark species that also cross‐amplified in <em>S</em>.
 <em>lewini</em> [Cli‐12 from <em>Carcharhinus</em>
 <em>limbatus</em> (Keeney & Heist, 2003) and SMO3,
 SMO7, and SMO8 from <em>Sphyrna</em>
 <em>mokarran</em> (Feldheim et al., 2020).
 Electrophoresis of amplified microsatellite loci was performed on
 an Applied Biosystems 3130 Genetic Analyzer. Alleles were sized using
 GeneScan LIZ 600 size standard and scored using the software GeneMapper
 v.3.7 (Applied Biosystems Inc.). Feldheim, K. A., Jabado, R. W., Chapman, D. D., Cardeñosa, D., & Maddox, J. D. (2020). Microsatellite primer development in elasmobranchs
 using next generation sequencing of enriched
 libraries. Molecular Biology
 Reports, 47(4), 2669–2675. Keeney, D. B., & Heist, E. J. (2003). Characterization of microsatellite loci isolated
 from the blacktip shark and their utility in requiem and hammerhead
 sharks. Molecular Ecology
 Notes, 3(4), 501–504. Nance, H. A., Daly‐Engel, T. S., & Marko, P. B. (2009). New microsatellite loci for the endangered
 scalloped hammerhead shark, <em>Sphyrna</em>
 <em>lewini</em>. Molecular Ecology Resources, 9(3), 955–957.
description: This dataset consists of two files: 1) Harned
 et al._msats_ETP.csv: contains microsatellite genotypes of young-of-year
 scalloped hammerhead sharks collected from the Eastern Tropical
 Pacific. 2) Harned et al_msats_GalFLSey.csv: contains
 microsatellite genotypes of all putative adult scalloped hammerhead
 sharks collected from the Galápagos, Florida east Coast USA, and the
 Seychelles.