Previous studies of population genetic structure inDissostichus eleginoideshave shown that oceanographic and geographic discontinuities drive in this species population differentiation. Studies have focused on the genetics ofD.eleginoidesin the Southern Ocean; however, there is little knowledge of their genetic variation along the South American continental shelf. In this study, we used a panel of six microsatellites to test whetherD.eleginoidesshows population genetic structuring in this region. We hypothesized that this species would show zero or very limited genetic structuring due to the habitat continuity along the South American shelf from Peru in the Pacific Ocean to the Falkland Islands in the Atlantic Ocean. We used Bayesian and traditional analyses to evaluate population genetic structure, and we estimated the number of putative migrants and effective population size. Consistent with our predictions, our results showed no significant genetic structuring among populations of the South American continental shelf but supported two significant and well-defined genetic clusters ofD.eleginoidesbetween regions (South American continental shelf and South Georgia clusters). Genetic connectivity between these two clusters was 11.3% of putative migrants from the South American cluster to the South Georgia Island and 0.7% in the opposite direction. Effective population size was higher in locations from the South American continental shelf as compared with the South Georgia Island. Overall, our results support that the continuity of the deep-sea habitat along the continental shelf and the biological features of the study species are plausible drivers of intraspecific population genetic structuring across the distribution ofD.eleginoideson the South American continental shelf.

Estimating genetic diversity and population structure with polymorphic markers might provide information for the better management of fish that have economic importance. We used the Chilean jack mackerel, Trachurus murphyi, a pelagic species distributed in the south Pacific Ocean, to test the population genetic structure across its distribution. A total of 522 samples were collected from 11 locations in 2008, to be analyzed using six loci microsatellites. We conducted traditional genetic analyses to describe the genetic diversity of T. murphyi and whether it shows spatial genetic structure. The results showed a high genetic diversity across locations (Ho = 0.551 to 0.980; He = 0.676 to 0.959). Estimates for the population structure showed a low and non-significant pairwise F_ST in all comparisons. We supported the non-genetic differentiation previously reported with the used microsatellite panel. Further comparative temporal studies should be conducted to identify the stability of this pattern. Overall, this study reinforces the hypothesis that, in the Pacific Ocean, Chilean jack mackerel correspond to a large single population.

Trachurus murphyi have been studied for population genetic structures for decades, identifying only one large population across the South Pacific Ocean. Although all of these studies have extensively examined the spatial genetic pattern, there remains a gap in understanding the potential role of temporality. Our study aims to elucidate spatial and temporal genetic patterns in T. murphyi populations in the South Pacific Ocean, examining genetic composition across seasons, including feeding and spawning seasons, where the latter was not previously investigated. Using 10 microsatellite loci, our study confirms an overall consistent and stable population genetic pattern in T. murphyi across its geographic distribution observed over multiple years and seasons. The only exception was found for New Zealand in the spring–summer season. Furthermore, we identify potential genetic markers for monitoring variability in the species.