Genetic Analysis of Striped Marlin (Tetrapturus audax) Population Structure in the Pacific Ocean

Abstract

Restriction fragment length polymorphism (RFLP) analysis of mitochondrial DNA (mtDNA) was used to determine the magnitude of intraspecific genetic differentiation among samples of striped marlin (Tetrapturus audax). Composite genotypes, representing information from 11 restriction endonucleases, were generated for samples of approximately 40 striped marlin each from Mexico, Ecuador, Australia, and Hawaii. Genotypic variation was relatively high in all samples: the pooled nucleon diversity was 0.82 (sample range 0.69–0.84), and the pooled nucleotide sequence diversity was 0.30% (sample range 0.20–0.32%). Values of corrected mean nucleotide sequence divergence between samples were low (0.01–0.06%, mean 0.03%). Despite low intersample divergences, significant heterogeneity was observed in the distribution of composite mtDNA genotypes among samples. Each location was characterized by the presence of unique genotypes at elevated frequencies. Samples taken from the same location 1 yr apart demonstrated temporal stability of the distribution of genotypes at that site. These results demonstrate significant spatial partitioning of genetic variation within striped marlin, a situation that sharply contrasts with similar studies of several species of tuna. Management should focus on units smaller than those currently used to conserve unique genetic variation within the species.