We can easily to observe the deep scattering layer (DSL) by acoustic Doppler current profiler (ADCP) or quantitative echo sounder, but do we really know what the DSL is? Is it the thermocline, phytoplankton, zooplankton, fish or any other matter? In this summer school, students will identify the DSL by the various sampling gears. CTD (temperature, salinity and conductivity) and water sampling can define thermoclines, nutrients, oxygen maxima and subsurface chlorophyll maximum. Zooplankton net sampling can collect zooplankton patches in the subsurface layers around the DSL. Trawl net sampling can collect fishes and their larvae from the deep layers. Participants will have a chance to obtain experience in oceanographic observations and apply data analyses to understand the interactions between physical and biogeochemical environments and marine ecosystem in coastal regions.