GENETIC-ANALYSIS OF THE POPULATION-STRUCTURE OF YELLOWFIN TUNA, THUNNUS-ALBACARES, FROM THE PACIFIC-OCEAN

The genetic basis of the population structure of yellowfin tuna, Thunnus albacares, in the Pacific Ocean was investigated with restriction fragment length polymorphism (RFLP) analysis of mitochondrial DNA (mtDNA). Samples of 20 yellowfin tuna were examined from each of five Pacific locations and one Atlantic location. MtDNA analysis with 12 informative restriction endonucleases demonstrated considerable genetic variation, as evidenced by an overall nucleon diversity of 0.84 and a mean nucleotide sequence diversity of 0.91%. Estimates of within-sample variation were remarkably consistent across all six locations. Despite high levels of variation, there was no evidence of genetic differentiation among samples. Common genotypes occurred with similar frequencies in all samples, and, with one exception, all genotypes that were represented by more than one individual occurred at more than one location. We could not reject the null hypothesis that all yellowfin tuna share a common gene pool. Our results are consistent with the alternate hypothesis that there is sufficient gene flow within the Pacific, as well as between the Atlantic and Pacific oceans, to prevent the accumulation of significant genetic differentiation.