Oceanographic Drivers of Larval Transport Variability in South Atlantic Jasus paulensis Populations

Effective fisheries management requires an understanding of the key influences on population variability. A fundamental driver of variability, particularly for isolated island populations, is the transport of planktonic early-life stages. Here, we use numerical modeling tools to investigate the role of oceanographic variability in the transport of Jasus paulensis (Tristan rock lobster) larvae in the southeast Atlantic. Model simulations highlight a lack of upstream sources for populations at the Tristan da Cunha (TdC) archipelago, suggesting a dependence on local retention and regional-scale transport between the islands. Model results indicate that years with poor retention in the northern island group are moderated by regular imports of larvae from Gough Island (GI), which suggests greater reliability in larval supply to the northern island group. However, GI rarely receives imports of larvae from elsewhere and the population is therefore dependent on retention of locally produced larvae. Periods of stronger eastward flows through the region, driven by stronger northerly and westerly winds, are associated with broadly reduced larval retention throughout the archipelago, and reduced northward export of larvae from GI, although the response at the northern island group is mixed and dependent on the timing of the strengthened flows. These results suggest that periods of stronger westerly winds through more frequent and intense El Niño events may have a negative impact on J. paulensis populations in the Tristan archipelago. Our findings provide insight into regional population connectivity dynamics and responses to environmental variability and change, to support management of the J. paulensis fishery.