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    Development of a spatially-explicit minimum realistic model for Antarctic toothfish (Dissostichus mawsoni) and its main prey (Macrouridae and Channichthyidae) in the Ross Sea

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    S. Mormede, M. Pinkerton, A. Dunn, S. Hanchet and S. Parker (New Zealand)
    Submitted By:
    Mr Doug Cooper (CCAMLR Secretariat)

    To explore the potential effects of the toothfish fishery on the population dynamics of Antarctic toothfish and its main prey, grenadiers (Macrouridae) and icefish (Channichthyidae), we develop a spatially explicit model using a predator-prey suitability model for the Ross Sea Region. We model the age-based population dynamics of toothfish, grenadier, and icefish, and include natural mortality (M1) and predation mortality (M2), in addition to fishing mortality (F) on all three species. The model suggests that the predation release caused by the fishery effect on toothfish abundance is greater than the direct fishing mortality on both prey species and that icefish is expected to show a larger increase in biomass through time than grenadiers. It also suggests that a prey-suitability function is more likely than a Holling type II function to describe the predatory relationships in the model. We use the model to compare the predicted population changes with available abundance data for each species to develop hypotheses of the nature of the interaction. Whilst this model is in a development stage, it provides a useful tool for evaluating potential impacts of the fishery on key prey species, and for assessing and designing monitoring tools for fish species associated with the toothfish fishery. We recommend targeted sampling of toothfish for diet analysis, and the monitoring of icefish and grenadier populations in SSRUs 88.1H and 88.1K through the development of age frequencies (length measurements and aging).