Spatial distribution and population structure of juvenile Antarctic toothfish (Dissostichus mawsoni) in the South Shetland Islands

As most of biological and ecological features of the Antarctic toothfish have been provided almost exclusively by the recent fishery exploitation in the Ross Sea targeting adult fishes, the early life history of this species is fragmentary and still needs to be fully addressed. Aiming to fill this gap, we provide new insights on the spatial distribution and population structure of juvenile D. mawsoni caught during bottom trawl surveys on the shelves around the South Shetland Islands (CCAMLR Subarea 48.1). Juveniles were relatively evenly distributed on the northern shelf of the South Shetlands and all around Elephant Island, with a few specimens caught in the Bransfield Strait. Although the specimens were caught in all depth strata surveyed, they were most abundant between 100 and 300 m depth, with an evident shift towards deeper waters with ontogeny. The sampled population consisted of 150 juveniles measuring between 22 and 78 cm TL, equally distributed between sexes, most of them with gonads at an immature stage of maturity. Both sexes showed a positive allometric body growth, indicating healthy body condition. Based on counts of annual growth increments from sagittal otolith sections, age estimates ranged between 2 and 7 years in males and between 2 and 8 years in females, respectively. Annual growth rate was estimated from the age-length keys, spanning from 5 to 10 cm TL. Integrating population structure with early life history of juvenile D. mawsoni, we provide some indication on connectivity between the investigated nursery area and potential neighbouring spawning areas.