Cross ocean-basin population genetic dynamics in a pelagic top predator of high conservation concern, the oceanic whitetip shark, Carcharhinus longimanus

Abstract

The oceanic whitetip shark, Carcharhinus longimanus, is a Critically Endangered, circumtropical, and highly migratory, pelagic shark. Yet, little information exists on its population genetic dynamics to guide conservation management practice. We present a first worldwide, mitochondrial and nuclear DNA assessment of the population genetic status of this imperiled species based on sequences of the complete mitochondrial control region (n = 173) and partial ND4 gene (n = 172), and genotypes from 12 nuclear microsatellites (n = 164). Statistically significant mitochondrial and nuclear DNA population genetic differentiation was detected across all marker datasets between Western Atlantic and Indo-Pacific oceanic whitetip sharks. Additionally, our data, combined with previously published, partial (701-base pairs) mitochondrial control region sequences from additional locations in the Atlantic and Indian Oceans, confirmed significant matrilineal population structure between the Western and Eastern Atlantic. The combined data also provisionally (i.e., with F_ST but not Φ_ST) indicated differentiation between Western North and Central-South Atlantic sharks, pointing to the need for further assessment in this region. Matrilineal differentiation was also detected between Indian and Pacific Ocean sharks via pairwise analyses, albeit with the ND4 gene sequence only (Φ_ST = 0.051; F_ST = 0.092). Limited sampling in the Pacific leaves open questions about the connectivity dynamics in this large region. Despite the presence of geographic population genetic structure, the mitochondrial data showed no evidence of across ocean basin phylogeographic lineages. A provisional assessment of mitochondrial and nuclear genetic diversity indicated the oceanic whitetip shark’s status falls in the middle to upper ranges compared to other shark species, potentially lending some optimism for the present adaptability and resiliency of this species if strong conservation measures are effectively implemented.