Testing the connectivity of Dissostichus eleginoides (Patagonian toothfish) between the Pacific coast of southern Chile and the Patagonian Shelf in the southwest Atlantic

Patagonian toothfish, Dissostichus eleginoides, are endemic to the Southern Hemisphere and are commonly associated with sub-Antarctic Islands and seamounts. They are found around the Falkland Islands and an economically valuable long-line fishery, targeting adult toothfish, operates in the Falkland Island Conservation Zones year round. This research explores gaps in the understanding of toothfish early life history by conducting egg buoyancy experiments and particle tracking simulations to resolve important spawning locations, transport pathways and larval retention areas. Buoyancy of toothfish eggs was estimated up to 21 days post fertilisation. Egg buoyancy followed a similar pattern to other species, where buoyancy initially decreased for several days before returning toward its initial value, although further data is needed to confirm this. Particle tracking simulations were undertaken using the software ICHTHYOP. Particles were released from potential spawning areas around the Burdwood Bank and southern Chile during July 2009 and 2012. These simulations represented spawning corresponding to a good and poor recruitment year respectively. Results of these particle tracking simulations for 2009 and 2012 suggest that transport from the Burdwood Bank is unlikely to be a major contributor to the recruitment of juveniles around the Falkland Islands or the Patagonian Shelf, with low connectivity (50%), indicating that larval transport from southern Chile to this area may be important for successful recruitment of juveniles around the Falkland Islands. Connectivity between these areas was weaker in 2012, potentially due to changes in the position and/or density of the boundary current that flows around southern Chile, forced by changes in the phase of the Southern Annular Mode (SAM). These findings have implications for fisheries management due to the connectivity of early life stages between Chile and the Patagonian Shelf region. Depletion of spawning stock biomass in Chile could impact potential recruitment in the South Atlantic, therefore a co-ordinated management strategy between Chile and the Falkland Islands should be considered