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

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.