Global-Scale Genetic Population Structure and Diversity in the Oceanic Whitetip Shark, Carcharhinus longimanus

The oceanic whitetip, Carcharhinus longimanus , is a circumtropical, pelagic shark of high conservation concern (IUCN Red List: "Critically Endangered" in the W North and W Central Atlantic and "Vulnerable" globally). We present an updated assessment of the global population structure, genetic diversity, and demographic history of this shark based on analysis of two mitochondrial genome regions (whole control region and partial NADH dehydrogenase subunit 4 (ND4) gene) and nine nuclear microsatellite loci. No population differentiation was detected between the north and south Atlantic. However, significant structure was consistently detected between the Western Atlantic and Indo-Pacific Oceans across both mitochondrial and nuclear markers. This population structure was coupled with deep geographic mitochondrial haplotype mixing and evidence of contemporary migration between the Western Atlantic and Indo-Pacific Oceans. We theorize that semi-permeable thermal barriers are responsible for the differentiation between the Western Atlantic and Indo-Pacific. Additionally, a signal of matrilineal structure between the Indian and the Pacific Oceans was detected with AMOVA and pairwise analyses of the ND4 gene (pairwise ΦST = 0.051, P = 0.046; pairwise Jost's D = 0.311, 95% CI = 0.020, 0.061). Relatively low mtDNA genetic diversity (concatenated mtCR-ND4: π = 0.32% ± 0.17%) compared to other globally distributed elasmobranch species raises concern for the future genetic health of these populations. Overall, despite the global distribution and high mobility of C. longimanus , significant population structure exists between the Western Atlantic and Indo-Pacific Oceans, and effective management strategies must take this into consideration.