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    Large-scale pelagic acoustic ecoregionalisation in the eastern part of the sub-Antarctic region

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    Número de documento:
    WG-EMM-2023/51
    Autor(es):
    F.E. Dakwa, F. Shabangu, L. Izard and A.B. Makhado
    Presentado por:
    Dr Azwianewi Makhado (Sudáfrica)
    Aprobado por:
    Dr Azwianewi Makhado (Sudáfrica)
    Resumen

    Acoustic data greatly improves spatial resolution in determining marine ecosystem structures, biodiversity assessments, trophic level interactions and identification of ecosystem functional groups within the Ocean down to species level. Acoustic data can prove qualitative and quantitative information about the distribution and abundance of functional groups within marine ecosystems. Acoustic data was collected aboard the SA Agulhas ll cruise trip from Cape Town to Prince Edwards Islands (PEI) and back between April and May 2017, 2018, and 2021. An EK60 echo-sounder was used to collect the acoustic data across three transducer frequencies: 38, 120, 200 kHz. 

    The aim is to determine the spatial-temporal distribution of marine organisms within the Southern Ocean using acoustic backscattering values. Although this paper does not identify any specific functional marine groups but continuous acoustic backscatter values with the fine resolution are going to be used to potentially determine changes in marine organisms within the Southern Ocean. The SA Agulhas ll passes three oceanic fronts between Cape Town and PEI and the Southern Ocean is divided by fronts into different biophysical zones inheriting different properties.  This paper aims to show the difference in marine organism aggregation across the different frontal zones. Previous studies have shown a relationship between acoustic backscatter values (Sa) with environmental factors. In this study, we are going to try and find a correlation between satellite-derived oceanographic factors and the distribution of acoustic backscatter. Vertical acoustic assessment and temporal distribution of acoustic data (day/night) are also going to be carried out to potentially show the diel migration and layering of marine organisms.

    Further data might be acquired to increase the longitudinal coverage of the data to encompass more of the Sub-Antarctic region.