Inferring population structure of mackerel icefish (Champsocephalus gunnari) between South Orkney Islands shelf and South Georgia shelf, Antarctic using otolith ecomorphological analyses

As an important species in the Southern Ocean , the mackerel icefish ( Champsocephalus gunnari ) is not only a major food source for a wide range of top predators, but also a predominant consumer of a key species, Antarctic krill ( Euphausia superba ), in the Southern Ocean ecosystem. In the Scotia Sea, this species is commercially harvested at South Georgia. However, the studies on the population structure of this species are inconclusive. Combining Trait Probability Density and Ecological Niche Modeling analyses on otolith shape, this study investigated the diffidence in populations of C. gunnari between the South Orkney Islands shelf and South Georgia shelf. Significant differences were identified in the otolith shape characteristics and ecological niches of fish from these two regions, with otolith roundness and aspect ratio likely being the primary factors responsible for these differences. The results of these analyses indicate that populations are separated between the two regions. This multi-dimensional approach offers new insights for otolith study and valuable data for understanding the ecological niche and population structure of fish species, thereby enhancing our ability to effectively manage and conserve C. gunnari populations. • Trait Probability Density and Ecological Niche Modeling analyses were used to analyze otolith shape in Champsocephalus gunnari . • Populations of C. gunnari show strong separation between the shelfs of South Georgia and South Orkney Islands. • Otolith roundness and aspect ratio are the main factors behind the differences. • Morphological changes linked to regional hydrography explain the population structure of C. gunnari .