Three complete mitochondrial genomes of shortfin mako sharks, Isurus oxyrinchus, from the Atlantic and Pacific Oceans.

We present complete mitogenome sequences of three shortfin mako sharks (Isurus oxyrinchus) sampled from the western Pacific, and eastern and western Atlantic oceans. Mitogenome sequence lengths ranged between 16,699 bp and 16,702 bp, and all three mitogenomes contained one non-coding control region, two rRNA genes, 22 tRNA genes, and 13 protein-coding genes. Comparative assessment of five mitogenomes from globally distributed shortfin makos (the current three and two previously published mitogenomes) yielded 98.4% identity, with the protein-coding genes ATP8, ATP6, and ND5 as the most variable regions (sequence identities of 96.4%, 96.5%, and 97.6%, respectively). These mitogenome sequences contribute resources for assessing the genetic population dynamics of this endangered oceanic apex predator.

Genetic population dynamics of the critically endangered scalloped hammerhead shark (Sphyrna lewini) in the Eastern Tropical Pacific.

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.