Scattering layer as recorded on an echo sounder paper is caused by the difference between the water mass and the presence of zooplankton.
In this paper, the relationship between the scattering layer and some hydro-biological factors in the South China Sea is discussed based on the records obtained during the survey cruises of RV CHANGI in April, June, and September, 1972. The diurnal vertical movement of scattering layer and the composition and biomass of zooplankton are also discussed.