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    Population structure and connectivity of an important pelagic forage fish in the antarctic ecosystem, Pleuragramma antarcticum, in relation to large scale circulation

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    Document Number:
    WG-FSA-12/23
    Author(s):
    J.W. Ferguson (USA)
    Submitted By:
    Sarah Mackey (CCAMLR Secretariat)
    Agenda Item(s)
    Abstract

    Ocean circulation has been identified as a major process controlling the distribution of biological material in marine systems.  Large-scale transport by the Antarctic Circumpolar Current (ACC), the Ross and Weddell Gyres, and the Antarctic Coastal Current can promote spatially complex population structure in the Southern Ocean through advection.  Antarctic silverfish (Pleuragramma antarcticum), a pelagic, neutrally buoyant notothenioid fish species, are distributed around the shelf systems of Antarctica and are considered an important species rivaling krill as prey for many birds, seals, whales, and other fish. We asked whether silverfish are distributed in independent, discrete populations along the shelf systems of the Southern Ocean or whether the large-scale circulation has led to connectivity among populations.  Hypotheses were tested by measuring the chemistry, trace elements and stable isotopes, in silverfish otoliths, and comparing the chemistry with simulated particle transport using a high resolution circulation model.  The results showed strong heterogeneity indicating four separate populations: i) in the Ross Sea, ii) on the southern Antarctic Peninsula in Marguerite Bay and off Charcot Island, iii) off Joinville Island, and iv) around the South Orkney Islands. This suggested that silverfish are not transported by the ACC, shelf processes on the West Antarctic Peninsula (WAP), or along the Weddell Front.  Using the circulation model, we built spatially explicit predictions of advective supply to areas along the WAP, and examined how interactions between silverfish life history and the Antarctic Coastal Current may structure assemblages over the continental shelf.