The effect of the suspended solid concentration on the daytime vertical distribution of Euphausia pacifica in the Yellow Sea, Korea

The Yellow Sea, characterized by a high concentration of suspended solids, is a semi-enclosed, marginal sea and shallow water in the northwestern Pacific Ocean, located between the Korean Peninsula and China. In this paper, we describe the response of acoustically determined weighted mean depth (WMD) of the krill, Euphausia pacifica, to variations in suspended solid concentration (SSC) during the daytime in spring and summer. E. pacifica was identified from the difference in the volume backscattering strength at 38 and 200 kHz. Our results indicated a correlation between the WMD of E. pacifica and the density of SSC during the daytime in both spring and summer. E. pacifica aggregation was distributed mainly near the bottom when the SSC was relatively low, but did not descend to the bottom when the SSC was relatively high. This implies that the SSC may be an important environmental factor affecting the behavior of E. pacifica.