Temporal and spatial distribution characteristics of Antarctic krill (Euphausia superba) aggregations in South Shetland Islands in autumn and winter of 2019

To further study the temporal and spatial distribution characteristics of Antarctic krill (Euphausia superba) aggregations in the waters near the South Shetland Islands, based on the acoustic surveys of Chinese E. superba production fishing vessels and commercial fishing data in the 2018/2019 fishing seasons, the center depth, water temperature and morphology of E. superba aggregations were analyzed. The results showed that there were significant temporal and spatial differences in the depth of E. superba aggregations center, the temperature at the depth of Antarctic krill aggregations and aggregations morphology in the waters near the South Shetland Islands (P<0.05). The average aggregations center depth, whose variation range was 34.39 to 86.12 m, showed an increasing trend from April to July, the difference between day and night was small (P=0.325), and the peak periods were sun rising (SRS) and night (NIT), which were 64.06 and 65.32 m respectively. The low value range of average aggregations center depth was 62.75°−63.75°S and 58.25°−59.75°W, and the high value range was 61.75°−62.25°S and 60.25°−61.75°W. The average temperature at the depth of E. superba aggregations, whose variation range was −1.71 to −1.50 °C, showed a decreasing trend from April to July. The peak period was NIT and evening twilight (ETW), which were −1.46 °C and −1.40 °C respectively. The low value range of average aggregations water temperature was 62.75°−63.75°S and 61.25°−61.75°W, and the high value range was 61.75°−62.25°S and 58.25°−60.75°W. The cluster shape was mainly stripped from April to May and scattered from June to July. The cluster shape was mainly horizontal band from day to afternoon (AFT), and the cluster shape was mainly scattered from sunset (SST) to morning (MRN). The results showed that there were obvious temporal and spatial differences in the depth of E. superba cluster center, cluster water temperature and cluster shape in the waters near the South Shetland Islands. The difference between months was greater than that between day and night, and had relative consistency in spatial variation.