Spatial distribution and biomass of pelagic fish in the East China Sea in summer, based on acoustic surveys from 1997 to 2001

Annual acoustic surveys were conducted using a quantitative echo sounder (frequency: 38 kHz) in the East China Sea from July to September of 1997–2001. Three groups of fish were identified from the echograms, based on school shape and swimming depth characteristics: (i) anchovy Engraulis japonicus and round herring Etrumeus teres; (ii) jack mackerel Trachurus japonicus and chub mackerel Scomber japonicus; and (iii) lantern fish Diaphus spp. and pearlside Maurolicus japonicus. The area backscattering strength (Sa) of each group was divided by the total weight of fish species caught in midwater trawls. Anchovy, round herring, jack mackerel, lantern fish and pearlside were the most abundant. The estimated biomass indices of anchovy and round herring were positively correlated with the commercial landings of these species, indicating the usefulness of acoustic surveys.