Acoustic Estimation of Biomass and School Character of Anchovy Engraulis japonicus in the East China Sea and the Yellow Sea

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  • Acoustic Estimation of Biomass and School Character of Anchovy <i>Engraulis japonicus</i> in the East China Sea and the Yellow Sea
  • Acoustic Estimation of Biomass and Scho
  • Acoustic estimation of biomass and school character of anchovy in the East China Sea and the Yellow Sea.

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The biomass of anchovy Engraulis japonicus in the East China Sea and the Yellow Sea was estimated by using a quantitative echo sounder (Furuno FQ-70) combined with the analysis of midwater trawling catches. The shape of anchovy schools were calculated from echograms. The acoustic survey, conducted in May and June 1992, was executed along 7 east-west transect lines ranging from latitude 30° 00' to 35° 45' N. Trawling was made at 5 areas. Over the 5 trawling areas, 97.8% of caught fish were anchovy in the daytime, but the percentage of anchovy decreased to 67.4% at night. Anchovy behaviour differed between day and night. In the daytime anchovy compactly shoaled inmidwater or nearbottom layers with the mean packing density of 53.6g/m3. The mean vertical height and the mean horizontal width of anchovy schools in the daytime were 3.3 (±3.4, S. D.)m and 16.3 (±7.7)m, respectively. At night, they were scattered at midwater or surface water layers. The total biomass of anchovy over the survey area was estimated to be 1, 960, 000 tons using TS kg=-31.4 dB/kg (204, 289km2). Some problems inherent with acoustic method for the estimation of the biomass are discussed.

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