Population structure of Antarctic toothfish, Dissostichus mawsoni from Areas 58 and 88 in the Antarctic Ocean using microsatellites and genome-wide SNPs

The Antarctic toothfish, Dissostichus mawsoni, serves as a valuable fishery resource around the Antarctic Ocean, managed by the Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR) since 1997. Although delimitating the population structure of this species is crucial for improving fishery management, its number of populations or genetic stocks still remain ambiguous. In the present study, we examined the level of genetic diversity and population structure of the Antarctic toothfish in Areas 58 and 88 by using a combination of the Patagonian toothfish specific (N=7) as well as our developed Antarctic toothfish microsatellite markers (N=7). We further performed population genomic analysis of the 58 (N=48) and 88 (N=54) samples of an average of 9.5 Gb per individual using approximately 141,000 SNPs (Single Nucleotide Polymorphisms). The level of microsatellite diversity in the Areas 58 and 88 tended to be higher in populations from the Ross Sea region MPA (marine protected area) than in those from the non-MPA. Population structure analyses of 14 microsatellites suggest a well-admixed shared gene pool in Areas 58 and 88 probably due to high contemporary gene flow during the prolonged epipelagic larval phase of this fish. However, given weak, but significant microsatellite differentiation found between 22 population-pairs (58 vs. 88; 17 pairs, within 88; 5 pairs) implies the possibility of the existence of distinct genetic stock or lineages (particularly for between Areas 58 and 88 populations) could not be excluded. Genetic differentiation and IBD (Isolation by Distance) patterns are clearly more evident in Antarctic toothfish markers than in Patagonian toothfish markers, suggesting that Antarctic toothfish markers would provide a higher resolution for detecting its population structure. The results of PCA based on SNPs showed two genetic clusters, formed by other factors rather than the sea areas. The findings of this study will inform conservation efforts on the stock (unit) management for this valuable fishery resource.