Population structure of bigeye tuna ( Thunnus obesus) in the South China Sea, Philippine Sea and western Pacific Ocean inferred from mitochondrial DNA

The population structure of bigeye tuna ( Thunnus obesus) in the South China Sea, Philippine Sea and western Pacific Ocean was investigated using sequence data of the first hypervariable region (HVR-1) of the mitochondrial control region. Nucleotide diversities, ranging from 3.8% in the Philippine Sea to 4.3% in the western Pacific Ocean, and haplotypic diversities, ranging from 0.998 in the South China Sea to 1.000 both in the Philippine Sea and western Pacific Ocean, are high in all sampling regions. Both Tajima's D and Fu and Li's D statistics are non-significant, indicating the scenario of an effective large and stable population size. Neighbor-joining tree and minimum spanning network showed that the haplotypes from all three regions can be grouped into two lineages. Lineage I is the major lineage which consists of more than 88% specimens in each regional population, and no differences are found in the frequencies of these two lineages among the three regional populations. Analyses of the HVR-1 sequences revealed a very high gene flow between the three sampling regions ( Nm = 71.91–2479.68). Furthermore, all analyses indicate that bigeye tuna over the sampling area constitute a single panmictic population.