The Impact of Sea-Ice Drift and Ocean Circulation on Dispersal of Toothfish Eggs and Juveniles in the Ross Gyre and Amundsen Sea

Knowledge about the early life history of Antarctic toothfish (Dissostichus mawsoni) is still incomplete, particularly on the spatial and temporal extent of spawning and the subsequent transport of eggs, larvae, and juveniles from the offshore spawning areas to the continental shelf. This study used a high-resolution hydrodynamic model to investigate the impact of ocean circulation and sea-ice drift on the dispersal of eggs, larvae, and juvenile Antarctic toothfish. The virtual eggs were released on seamounts of the Pacific-Antarctic ridge in the Ross Gyre and advected using hydrodynamical model data. Particles were seeded annually over the years 2002–2016 and tracked for 3 years after their release. Recruitment success was evaluated based on the number of juveniles that reached known coastal recruitment areas, between the eastern Ross and Amundsen Seas, within 3 years. Sensitivities to certain juvenile behaviors were explored and showed that recruitment success was reduced by around 70% if juveniles drifted with sea-ice during the second winter season as this carried them into the open ocean away from the shelf region. Recruitment success increased during the second winter season if juveniles were entrained in the Ross Gyre circulation or if they actively swam toward the shelf. These modeling results suggest that the ecological advantage of sea-ice association in the early life cycle of toothfish diminishes as they grow, promoting a behavior change during their second winter.