Phylogeographic analysis of Thyrsites atun (Perciformes: Gempylidae) reveals connectivity between fish from South Africa and Chile

The snoek, Thyrsites atun, is a pelagic fish of the family Gempylidae that inhabits cold waters of the southern hemisphere. It is an important fishing resource species (e.g. Chile, Namibia, New Zealand) linked mainly to the artisanal fisheries, however, its phylogeographic and population aspects are largely unknown. In this study we provide the first detailed analysis of the phylogeographic patterns and demographic processes of the snoek for the southern hemisphere using mitochondrial data of the Cytochrome c Oxidase subunit I gene. Our results indicate two lineages: (i) Australia-New Zealand, and (ii) Chile-South Africa-Namibia. The Australia-New Zealand clade shows partial isolation between populations associated with distinct biogeographic regions, likely driven by the region's oceanography. The divergence between the lineages happened similar to 800,000 years ago. On the other hand, analysis of the fish caught in the South-eastern Pacific (Chile) showed that the genetic diversity among localities (hT=0.657) was lower than within localities (hS=0.664), which was consistent with the pairwise comparisons results, suggesting the absence of phylogeographic structure. Based on our estimations, population expansion in T. atun would have occurred similar to 7.5ka (after LGM) under the Bayesian skyline plots approximation. We discuss the scope that this study could have in fisheries management of this important species.