Population Structure of Blue Marlin, Makaira nigricans, in the Pacific and Eastern Indian Oceans

Abstract

Blue marlin Makaira nigricans is economically important for fisheries worldwide. However, overfishing has substantially reduced the stock size. Better knowledge of blue marlin population genetics will help improve management and conservation. Previous genetic studies concluded that the Pacific blue marlin should be considered a single stock. This study investigated the population genetic structure of blue marlin inhabiting the Pacific and eastern Indian oceans based on mtDNA cytochrome b (cyt b) and control region (CR) sequence variation. We collected tissue samples (n = 183) from three Pacific and one Indian Ocean, and determined the sequences of 1140 bp of cyt b and 905 bp of CR. Phylogenetic analysis revealed that blue marlin contain two clades, the Atlantic clade and the ubiquitous clade, and that all the eastern Indian and Pacific individuals collected for this study belonged to the ubiquitous clade. All eastern Indian and Pacific blue marlin possess extremely high haplotype diversity (h) and low nucleotide diversity (pi). The results of pairwise Phi(ST), hierarchical analysis of molecular variance (AMOVA) and spatial analysis of molecular variance (SAMOVA) all support that there is no population differentiation among eastern Indian and Pacific blue marlin. Neutrality tests and pairwise mismatch distribution analysis both indicated that eastern Indian and Pacific blue marlin have undergone a rapid population expansion on the order of 0.30 to 0.65 million years ago (mya). This study demonstrates that blue marlin in the Pacific and eastern Indian oceans constitute a single stock. International cooperation will be required to preserve blue marlin as a resource; moreover, the high genetic variation of blue marlin in this region suggests that unique haplotypes in the population are sensitive to high harvesting levels and could disappear.