Biology Faculty Articles
Genetic population dynamics of the critically endangered scalloped hammerhead shark (Sphyrna lewini) in the Eastern Tropical Pacific
Ecology and Evolution
aggregations, conservation, Galápagos, genetic diversity, philopatry
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-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 = 1818 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.
This study was supported by the Save Our Seas Foundation, Guy Harvey Ocean Foundation, the Swiss Shark Foundation/Hai-Stiftung, National Geographic Pristine Seas, the Gordon and Betty Moore Foundation, the NSU Department of Biological Sciences, the Mark and Rachel Rohr Foundation, Co-Exist Projects and donor Mark Qi Wong. Samples from the Eastern Tropical Pacific were acquired under CITES Permits 18EC0117/BG (Ecuador), 2018-CR4142/SJ (Costa Rica), SEX-A-35-18 (Panama), CO43891 (Colombia), 18EC000003/PG (Galápagos). We are grateful to the Galápagos National Park Directorate for the institutional support. This research was conducted in the Galápagos Marine Reserve under research permits PC-27-17 & PC-46-18 granted to Dr. Pelayo Salinas de León from the Charles Darwin Foundation, and under the Ecuadorian Ministry of Environment agreement to access genetic resources MAE-DNB-CM-2016-0043. We thank D. Abercrombie, D. Chapman, Simon Gulak, Lori Hale, John Nevill, Linda Noll, and Rachel Wilborn for contributing adult shark samples from Florida and Seychelles to our study. This is contribution number 2477 from the Charles Darwin Foundation for the Galápagos Islands.
Creative Commons License
This work is licensed under a Creative Commons Attribution 4.0 International License.
Harned, Sydney P.; Andrea Bernard; Pelayo Salinas-de-Leon; Marissa Mehlrose; Jenifer Suarez; Yolani Robles; Sandra Bessudo Lion; Felipe Ladino; Andrés López Garo; Ilena Zanella; Kevin A. Feldheim; and Mahmood Shivji. 2022. "Genetic population dynamics of the critically endangered scalloped hammerhead shark (Sphyrna lewini) in the Eastern Tropical Pacific." Ecology and Evolution 12, (12): e9642. doi:10.1002/ece3.9642.
DATA AVAILABILITY STATEMENT
All mitochondrial data underlying our analyses can be accessed at https://www.ncbi.nlm.nih.gov/ (GenBank Accession Numbers: OK082068-OK082075). Microsatellite genotypes are available from Dryad at https://doi.org/10.5061/dryad.7m0cfxpzr.