Population genetic structure of the commercially important Hawaiian grouper Epinephelus quernus (Serranidae) using mitochondrial and nuclear microsatellite DNA

The Hawaiian Grouper, Epinephelus quernus, is one of several commercially important species of bottomfish occurring in Hawaiian waters. Endemic to the Hawaiian archipelago extending approximately 1,500 miles, and to nearby Johnston Atoll lying several hundred miles to the South, E. quernus has become locally depleted off the waters of the Main Hawaiian Islands.; Questions concerning migration among islands became of central importance to the management of E. quernus, providing the impetus for this study.; Mitochondrial DNA analyses of 398 base pairs of the control region revealed small, but significant differences in allele frequencies among many islands, particularly among the island of Necker and Gardner, situated approximately midway through archipelago. Interestingly, many islands in the middle and upper chain harbored relatively high genetic diversity and unique alleles. Migration appears to be substantial between the Southeastern Islands and the Northwestern Islands, with lower migration between the middle islands of Nihoa and Necker. In addition, evidence of isolation by distance and historical population expansion was revealed by the various statistical tests conducted.; Nuclear DNA studies involved the isolation of a series of microsatellite fragments from a repeat-enriched DNA library. Five usable loci were obtained from E. quernus, and an additional five isolated from other serranids were used to increase the number of loci in the study. Frequency based analyses were generally consistent with those based on mtDNA, namely that comparisons among the middle archipelago and the Northwest and Southeast extremities showed small, but statistically significant differences, especially when analyzed under the stepwise mutation model. Isolation by distance across the archipelago and locally within islands was also evident from regression analyses of genetic differentiation against geographic distances. Significant heterozygote deficiencies suggest that despite reduction in abundances estimated from fishery catch statistics, no genetic evidence exists for severe population bottlenecks.; Based on the results of this study, it appears that migration across the archipelago is somewhat limited by geographic distance, and that oceanic currents may play a role in genetic structuring of E. quernus. Allele frequency differences suggest that the three existing management zones need to be slightly re-defined to better reflect stock structure. In addition, high diversity in the middle archipelago indicates a probable ancestral origin for the species, with more recent colonization and expansion into the Southern Main Hawaiian Islands and the Northwest extreme, such that additional considerations may be in order to properly manage the region's uniqueness. Given the results here, the decline in abundance as measured by the spawning potential ratio will likely require specific management strategies to rebuild stocks in the Main Hawaiian Islands. However, no evidence of genetic bottlenecks was apparent, hence, prompt management would likely ensure maintenance of a genetically healthy fishery. (Abstract shortened by UMI.)...