Biomass estimation of zooplankton communities and characteristics on deep scattering layer (DSL) in East China Sea

Hydroacoustic and open-closing zooplankton net survey were conducted to understand the characteristics of the deep scattering layer (DSL) and to estimate the density of and zooplankton in the DSL, in the northwestern part of the East China Sea. The survey was carried out during June 23-30, 2003 at 12 sampling stations for zooplankton. The vertical migration mechanisms of zooplankton are very variable to the taxa. In this study, after we grasp the vertical migration of zooplankton through results of echo-sounder we verify mechanisms of their vertical migration in the East China Sea, the southwestern regions and the southern Sea of Korea where the characteristics of currents are different. Also, to estimate effectively the biomass of zooplankton, we research the acoustic scattering strength according to the species. On the basis of these results we devise the most effective method for estimating zooplankton biomass through comparing and analyzing estimated by a net and echosounder. We obtained the results by a net, as a follows: zooplankton abundance ranged from 21 to 175 indiv./m³. Copepods made up about 44.1 (station 6) to 91.1% (station 1). Euphausiids were abundant at stations 3 (14.2%) and 5 (29.2%) and amphipods were consist of > 21% at stations 4, 6, 7. Sagittoids were abundant >12.0% at stations 4 and 9. Other taxa were very low <10 %, although fish eggs were 11.1% at station 6