Assessing the Impact of Releasing Exogenous Hatchery-Reared Juveniles of Pacific Abalone, Haliotis discus

Abstract

We studied the impact of releasing exogenous hatchery-reared juveniles on populations in Pacific abalone based on 10 microsatellite loci at the population and individual level. Standard measures of genetic variation (R _S and H _E) for collections from Ezo-and Kuro-abalone habitats did not differ. However, samples from Ezo-and Kuro-abalone habitats, respectively, were clearly divided into genetically distinct clusters; a result that was consistent with the F _ST analysis. In population-assignment testing, most individuals collected from Kuro-abalone habitats, where intensive release of hatchery-reared Ezo-abalone juveniles have been carried out, were assigned to a genetically defined Kuro-abalone group, suggesting that most of exogenous hatchery-reared Ezo-abalone had difficulty reproducing successfully in Kuro-abalone habitats. However, in the warm-water sampling area stocked with the greatest number of exogenous Ezo-abalone hatchery-reared juveniles, the numbers of misassigned individuals were highest. This suggests that the reproductive contribution of stocked hatchery-reared Ezo-abalone cannot be ruled out completely. Therefore, hatchery-mediated introgression of exogenous Ezo-abalone genes into the Kuro-abalone subspecies remains a possibility. To support the goal of a genetically fit and sustainable abalone fishery, further detailed studies and evaluation of the potential impact of introgression are needed.

Keywords:

• genetic relationship
• Haliotis discus
• individual assignment
• microsatellite marker
• Pacific abalone
• impact of stocking

ACKNOWLEDGMENTS

We thank Dr. M. Sekino and Dr. T. Sugaya for advice on statistical analysis and Mr. S. Kikuch, Dr. H. Hoshikawa, Dr. T. Horii, Dr. T. Yamada, and Dr. M. Anzawa for providing abalone samples and identification of abalone based on morphology. We also thank two anonymous reviewers for their constructive comments on the draft manuscript. This work was supported by research project funds from the Fisheries Research Agency of Japan.

Notes

* (P < 0.05)

** (corrected significance level for 36 simultaneous tests,