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    Biomass of Antarctic krill around South Shetland using 2-dB difference method in April 2016

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    Número de documento:
    WG-EMM-16/60
    Autor(es):
    Delegation of the Republic of Korea
    Presentado por:
    Dr Seok-Gwan Choi (República de Corea)
    Aprobado por:
    Dr Seok-Gwan Choi (República de Corea)
    Punto(s) de la agenda
    Resumen

    Antarctic Krill plays an important role in Antarctic ecosystems as the medium that connects phytoplankton to penguins, seals, and whales. It is also in the limelight as an important protein source for the future food resource. Since Krill is mainly schooled within 200m depth, mass catching is operated by Norway, Korea, and Japan, etc. Major fishing area is the surroundings of South Sheltland where it is surrounded by Darke Passage in North, Weddle Sea in East, and Bransfield Strait in South. CCAMLR (Convention for the Conservation of Antarctic Marine Living Resources) is currently implementing a regulation that limits Krill catch amount using fishing survey and acoustic assessment data in order to utilize Krill resources continuously.

    This study is aimed to estimate the density and the biomass of Krill that inhabit in the surroundings of South Sheltland by using acoustics. An acoustic survey was conducted from April 13 to 24 in 2016 in the sea of South Sheltland using a commercial fishing vessel (GwangJa-Ho, 3,012 tonnage). Data on frequency 38 and 120 kHz (EK60, Simrad) were collected (survey area: 90,700 km2). Before the acoustic survey, the system correction (62°28.7‘S, 59°42.4’W) was made using a calibrated sphere with 60mm (frequency 38 kHz) and 23mm (frequency 120 kHz). Using an acoustic post-processing software (Echoview Ver6.0, Myriax), noises of collected data were processed and frequency differences were investigated by cell size (5ping*2m, 10ping*2m, 30ping*2m, 40ping*2m, 50ping*2m). In addition, the density and the biomass of Krill were calculated by applying frequency differences of Krill. The survey of fishing gears was conducted in seven stations of the sea where the acoustic survey had done using a midwater trawl. Samples were classified by species and catch amount, and the length of 200 Krills that were collected from each station was measured.

    Results of fishing survey showed that over 99% of Krills were caught in 6 stations except station 3 where all Electrona calsbergi were caught. The range of caught Krill's TL was 23.8~57.6mm. Frequency differences of Krill by station were 7.0~9.7 dB at 5ping*2m, 7.0~9.7 dB at 10ping*2m, 7.0~9.8 dB at 30ping*2m, 7.0~9.8 dB at 40ping*2m, and 7.0~9.8 dB at 50ping*2m. It did not show a big difference by cell size, but the shape of Krill was changed as the cell size became larger. The frequency difference (average) of Electrona calsbergi was estimated to be –2.1 dB in all cells, and frequency characteristics of Krill and Electrona calsbergi on frequency 38 and 120 kHz were clearly different. Krill was shown to be higher density within 500m in water depth, especially the school of Krill was largely found in Bransfield strait. The average density and the current biomass of Krill by station were estimated to be 0.08~344.92 g/m2 and 3 million tons (CV=39.4%), respectively.