Acoustic observation for seasonal variations of sound scattering layer (SSL) around the Yellow Sea, Korea

Abstract

The Yellow Sea Bottom Cold water (YSBCW :< 10&#61616;C) as a shelter for zooplankton through the hot summer (subsurface water temperature: > 25&#61616;C), is known as a major influence on the oceanic environment of the Yellow Sea. In this study, hydroacoustic surveys were carried out to know migration patterns of sound scattering layer (SSL) due to zooplankton patches during spring and summer seasons in 2010 and 2011, respectively. Acoustic data were obtained with various multi-frequency scientific echosounders; spring season (38, 200 kHz) 2010, summer season (200, 420 kHz) 2010, spring season (38, 200, 420 kHz) 2011, summer season (38, 200 kHz) 2011. Simultaneously, net samplings were collected to compare acoustic and zooplankton data. In order to understand seasonal migration patterns of the SSL, we mainly focused on the volume backscattering strength (SV). In spring season 2010, diel distribution of the zooplankton patches in the YSBCW area showed an apparently vertical migration pattern, that the SSL were moved from near the surface at night time to the bottom at day time. On the contrary, the SSL in the summer season 2010 (sea surface ~ 27&#61616;C) was migrated to the below thermocline at night time. In case of 2011, migration pattern during spring season was similar with that of spring season 2010. However, SSL in the summer season 2011 was migrated to near the surface due to